The biology of Canadian weeds. 117. Taraxacum officinale G. H. ...

The biology of Canadian weeds. 117. Taraxacum officinale 

G. H. Weber ex Wiggers 

S. M. Stewart-Wade 1,3 , S. Neumann 1,4 , L. L. Collins 2 , and G. J. Boland 1 

1 Department of Environmental Biology, University of Guelph, Guelph, Ontario, Canada N1G 2W1; 

2 Department of Plant Sciences, University of Western Ontario, London, Ontario, Canada N6A 5B7. 

Received 23 January 2001, accepted 18 June 2002. 

Stewart-Wade, S. M., Neumann, S., Collins, L. L. and Boland, G. J. 2002. The biology of Canadian weeds. 117. Taraxacum 

officinale G. H. Weber ex Wiggers. Can. J. Plant Sci. 82: 825–853. Taraxacum officinale G. H. Weber ex Wiggers (dandelion, 

pissenlit officinal) is a perennial weed occurring in parks, gardens, pastures, orchards, roadsides, vegetable gardens, agricultural 

crops and horticultural crops. A common weed worldwide, it was originally introduced from Eurasia and now occurs in every 

province of Canada. It is an aesthetic problem during flowering and seed production, interrupting turfgrass uniformity and density; 

it reduces yields of agricultural crops; it causes slower drying of hay; its pollen is allergenic; and it acts as an alternative host 

for several pests and diseases. A number of herbicides are available for its control. Mechanical removal of T. officinale plants has 

limited success, due to the regenerative capacity of the long taproot. Insects, fungi, sheep and geese have been considered as biological 

control agents for dandelion. 

Key words: Taraxacum officinale, dandelion, weed biology, Canada. 

Stewart-Wade, S. M., Neumann, S., Collins, L. L. et Boland, G. J. 2002. Biologie des mauvaises herbes au Canada. 117. 

Taraxacum officinale G. H. Weber ex Wiggers. Can. J. Plant Sci. 82: 825–853. Taraxacum officinale G. H. Weber ex Wiggers 

(pissenlit officinal, dandelion) est une adventice vivace qui peuple les parcs, les jardins, les champs, les vergers, le bord des routes, 

les potagers, les grandes cultures et les cultures horticoles. Cette mauvaise herbe, qu’on retrouve partout sur la planète, nous vient 

d’Eurasie et a désormais colonisé toutes les provinces du Canada. Elle pose un problème d’esthétisme lors de la floraison et de la 

production des graines, jetant une note de discordance dans le vert des pelouses et diminuant la densité des peuplements. Cette 

adventice réduit le rendement des cultures et ralentit le fanage du foin. Son pollen est allergène et la plante sert d’hôte de rechange 

à plusieurs ravageurs et maladies. Il existe divers herbicides pour la combattre. L’extraction des plants de T. officinale à la machine 

n’a qu’une efficacité restreinte à cause de la capacité de regénération de la longue racine pivotante. Les insectes, les champignons, 

les ovins et les oies figurent parmi les agents de lutte biologique contre le pissenlit. 

Mots clés: Taraxacum officinale, pissenlit officinal, biologie des mauvaises herbes, Canada 

1. Names 

Taraxacum officinale G. H. Weber ex Wiggers — dandelion; 

pissenlit officinal (Darbyshire et al. 2000), dandelion 

officinal, dent-de-lion, dent-de-lion commun, florion d’or, 

pissenlit dent-de-lion, pissenlit (Ferron and Cayouette 

1975); blowball, faceclock, dumble-dor (in Newfoundland), 

lion’s tooth, yellow gown, priest’s crown, pee-a-bed, wet-abed 

(Jackson 1982). Asteraceae, composite (daisy) family, 

tribe Cichoriae. 

The first scientific classification of T. officinale was by 

Linnaeus in 1753 as Leontodon taraxacum (Jaeger 1955). 

Wiggers (1746–1811) described the genus Taraxacum, and 

Georg Heinrich Weber created the current classification in 

3 Current address: School of Agriculture and Food Systems, 

Institute of Land and Food Resources, The University of 

Melbourne, Victoria, 3010, Australia. 

4 Current address: School of Bioscience, Division of 

Agricultural Sciences, Sutton Bonington Campus, 

University of Nottingham, Loughborough, Leicestershire, 

LE12 5RD, UK. 

825 

1780 (Britton and Brown 1970). The origin of the name 

Taraxacum is uncertain but Holm et al. (1997), Jenniskens 

(1984) and Mitich (1989) have reviewed possible sources. 

Taraxacum is thought to originate from the Arabic name for 

the dandelion “tarachakum” (meaning wild cherry), 

“tarakhshaqun” (meaning wild chicory), “tharachschakuh”, 

“talkh chakok” or “tarashqun” meaning “bitter herb” 

(Dwyer 1977; Jenniskens 1984; Mitich 1989). In another 

explanation, the name was derived from the Greek words 

“taraxis”, an eye disease, “tarassen” or “tarasos” meaning 

disorder, “trogimon” meaning edible and “akeomai” or 

“akos” meaning to cure or remedy (Powell 1972; Jenniskens 

1984; Mitich 1989). Officinale means medicinal or capable 

of producing medicine (Schmidt 1979), or “of the shops”, 

meaning it was sold as a remedy for man’s illnesses (Dwyer 

1977; Holm et al. 1997). 

The common name for dandelion is an alteration of “dent 

de lion”, a phrase thought to be based on the Welsh “Dant y 

Llew” of the thirteenth century (Hedrick 1972), meaning 

“tooth of the lion”. This name may have evolved because of 

the shape of the immature seeds (Lovell and Rowan 1991),

826 CANADIAN JOURNAL OF PLANT SCIENCE 

the jagged shape of the leaves (Jackson 1982), the appearance 

of the yellow florets of the inflorescence (Angier 

1980), or the strong white taproot (pulling it from a lawn is 

like trying to extract a lion’s tooth) (Dwyer 1977). The 

French name, pissenlit, is attributed to the diuretic activity 

of the plant parts (Lovell and Rowan 1991). 

2. Description and Account of Variation 

(a) Description. Taraxacum officinale is an almost stemless, 

lactiferous, perennial herb. The stems are acaulescent, only 

1–2.5 cm in length, with extremely short internodes at or 

below the soil surface (Gier and Burress 1942; Holm et al. 

1997). The leaves form a basal, radial rosette in which every 

sixth leaf overlaps (Holm et al. 1997). The leaves are highly 

variable in shape, ranging from lobeless to toothed edges 

to highly incised and, when lobed, the lobes point to the leaf 

base. The runcinate-pinnatifid or lobed oblanceolate leaves 

have glabrous to sparsely pubescent lower surfaces, are generally 

5–40 cm in length and 0.7–15 cm in width, and taper 

to a winged, petiolar base (Gleason 1963; Holm et al. 1997). 

The prominent midrib of the leaves ranges in colour from 

pale yellow-green to deep red-brown (L. L. Collins, unpublished 

data, University of Western Ontario, London, ON). 

The thick, branched taproot can be up to 2–3 cm in diameter 

and grow up to 1–2 m in length (von Hofsten 1954; 

Solbrig 1971). The lateral roots are arranged in two rows 

that wind clockwise downward in a loose spiral around the 

root and are distributed more or less regularly along its 

length (Gier and Burress 1942). 

The basal rosette gives rise to one to numerous glabrous, 

hollow, cylindrical scapes (peduncles), 5–50 cm tall, 

decreasing in diameter along their length from base to tip. 

Each scape bears a terminal capitulum (inflorescence) of 2–5 

cm diameter (Gier and Burress 1942; Gleason 1963; Holm et 

al. 1997). Each capitulum is subtended by an oval-cylindrical 

involucre with lanceolate-obtuse, green to brownish, 

herbaceous bracts, in two rows of phyllaries, with the outer 

phyllaries shorter and wider than the inner phyllaries (Holm 

et al. 1997). The inner phyllaries are of uniform length and 

one-serrate, while the outer ones are unequal, one-third to 

one-half as long as the inner bracts and many-serrate. All 

bracts are reflexed at maturity, with a convex, minutely pitted 

receptacle, without paleae (Holm et al. 1997). 

The capitulum is composed of up to 250 ligulate, perfect, 

yellow florets (Holm et al. 1997). Each floret has a corolla 

of five united petals with one side prolonged, strap-shaped, 

and five-notched at the tip. Each floret contains five stamens 

fused into a tube with a sagittate base, filiform basal lobes 

and an obtuse apex (Holm et al. 1997). The warty spherical 

pollen grains are 30 µm in diameter (Gier and Burress 1942). 

In each floret, the inferior ovary contains one basal, inverted 

ovule with a single integument. A single style branches 

into two stigmatic arms, which are 1–1.5 mm in length and 

0.06 mm in diameter, and covered with fine hairs (Gier and 

Burress 1942; Sood and Sood 1992; Holm et al. 1997). Each 

ovule gives rise to a pale grey-brown to olive-brown, narrowly 

obovoid-oblong, rough-surfaced cypsela (seed), 3–4 

mm in length and 1 mm width. Each cypsela is 5–8 ribbed 

on each side with upwardly pointed teeth at the beaked apex 

and with a white pappus composed of numerous hairs, 3–4 

mm in length, mostly white, persistent and fused at the base 

(Gleason 1963; Holm et al. 1997). In the remainder of this 

review, for the sake of simplicity, the following terms will 

be used: scape to describe a peduncle, inflorescence to 

describe a capitulum and seed to describe a cypsela. 

Taraxacum officinale ranges in ploidy level from diploid 

to hexaploid (x = 8), possessing 16 to 48 individual chromosomes 

(Richards 1973). North American individuals of 

this species are generally triploid (x = 8, 3x = 24), and sexual 

reproduction is rare or may even be absent (Solbrig and 

Simpson 1974; Lyman and Ellstrand 1984). Of the 2000 

reported micro-species in Europe, approximately 90% are 

polyploids that reproduce asexually by obligate agamospermy. 

The majority of the remaining 10% are diploid 

species that reproduce sexually and are obligate outcrossers. 

However, a small number of more primitive forms are capable 

of self-fertilization (Hughes and Richards 1985). 

(b) Morphological characters. Taraxacum officinale has 

similarities with other Taraxacum and related species. The 

red-seeded dandelion, Taraxacum laevigatum (Willd.) DC., 

reported throughout southern Canada, is similar to T. officinale, 

however, it is more slender, and its leaves are very 

deeply incised for their whole length (Gleason 1963). Leaf 

lobes of T. laevigatum are generally narrower than those of 

T. officinale and, unlike T. officinale, the terminal leaf lobe is 

seldom larger than lateral leaf lobes. Unlike seeds of T. officinale, 

seeds of this species become bright red to reddish purple 

at maturity (Gleason 1963). Taraxacum officinale is more 

difficult to distinguish from T. ceratophorum (Ledeb.) DC., 

which is found in northern mountainous regions of Canada 

(Gleason 1963). T. ceratophorum is generally less robust, 

has more broadly lobed petioles, leaves with fewer lobes, and 

smaller inflorescences than T. officinale (Gleason 1963). 

The marsh dandelion, Taraxacum palustre, found in 

southern and eastern Ontario and western Québec, is very 

similar to T. officinale. Originally reported as T. turfosum 

(Brunton 1989), it has since been placed in the well-defined 

species, T. palustre (Oldham et al. 1992). T. palustre can be 

distinguished by its erect, narrow, remotely serrate leaves 

and very dark, broad, and strongly appressed exterior 

involucral bracts (Brunton 1989; Oldham et al. 1992). 

There are also many native species of Taraxacum in 

North America, which mostly occur in the Arctic and eastern 

Canada. For example, T. lyratum (Ledeb.) DC. occurs 

throughout much of the Yukon territory as well as in 

Labrador and Newfoundland (Cody 2000). Other rare native 

species, such as T. latilobum and T. laurentianum, are found 

in eastern Québec, Newfoundland and Labrador, and these 

could be confused with T. officinale (J. Cayouette, personal 

communication, Agriculture and Agri-Food, Canada, 

Ottawa, ON). 

Taraxacum officinale is also morphologically similar to 

other members of the Asteraceae. Chondrilla juncea L., 

skeleton-weed, overlaps in range with T. officinale in the 

interior of British Columbia (R. S. Cranston, personal communication, 

BC Ministry of Agriculture, Fisheries and 

Food, Abbotsford, BC). While the basal rosette of C. juncea

is similar to that of T. officinale, C. juncea produces 

branched stems bearing linear cauline leaves, and subsessile 

inflorescences containing 11 florets each (Gleason 1963). 

Members of the genus Crepis L., hawk’s beard, have inflorescences 

bearing florets that are yellow, ligulate, and perfect. 

However, the inflorescences occur in small to large 

groups in an open, corymbiform or paniculiform arrangement. 

Basal leaves of Crepis species are also less lobed than 

those of T. officinale (Gleason 1963). Members of the genus 

Prenanthes L., white lettuce, have basal leaves that could be 

mistaken for the leaves of T. officinale. However, 

Prenanthes species also exhibit cauline leaves, scaled 

scapes and corymbiform, paniculiform, thyrsoid, or subracemiform 

inflorescences with ligulate and tubular florets, 

which are absent in T. officinale (Gleason 1963). The inflorescence 

of Tussilago farfara L., coltsfoot, is very similar to 

that of T. officinale, but flowering in this species occurs 

prior to the development of the leaves in the spring, while T. 

officinale produces inflorescences well after the establishment 

of leaves (Gleason 1963). Taraxacum officinale may 

also be confused with members of the genus Hypochoeris 

L., cat’s-ear, as well as with Leontodon autumnalis L., fall 

dandelion, due to the similarities of the bright yellow inflorescences 

of these species. Aarssen (1981) provided a key to 

distinguish these species. 

(c) Intraspecific variation. The taxonomy of T. officinale is 

complex and requires more extensive study (Small and 

Catling 1999). As Taraxacum species exhibit extremely 

variable biology and morphology, the genus is treated as 

many micro-species in Europe; however, it is treated as one 

species exhibiting considerable phenotypic plasticity in 

North America (Richards 1973). This extensive variation 

may be somewhat unexpected since North American populations 

are generally considered to be apomictic and so do 

not exchange genes (Solbrig and Simpson 1974; Taylor 

1987). There are differences of opinion regarding the extent 

to which the observed variation is due to phenotypic plasticity 

versus genotypic differentiation arising from multiple 

introductions of European microspecies (Taylor 1987). 

Janzen (1977) suggested that there is very little genetic variation 

among populations, while Abbott (1979) argued that 

this assumption is premature. Taylor (1987) stated that intrapopulational 

morphological variation was as great as or 

greater than inter-populational variation and, therefore, morphological 

variation was largely due to phenotypic plasticity. 

However, Kennison (1978) found that in populations 

from Washington State, variation among populations was 

consistently greater than variation within populations. 

Ford (1981a) observed that agamospecies growing in particular 

habitats differed from site to site in characters such as 

population flux, survivorship and fecundity. Furthermore, 

agamospecies represent ecologically highly specialized population 

units, relevant to a fine scale of heterogeneity of 

habitat, and two or more agamospecies can coexist in a 

broad habitat (Ford 1981b, 1985). Small and Catling (1999) 

provide an excellent summary of variation in this species in 

Canada. King (1993) used restriction enzyme analysis of 

ribosomal DNA and chloroplast DNA to assess the relative 

STEWART-WADE ET AL — TARAXACUM OFFICINALE G. H. WEBER EX WIGGERS 827 

contribution of hybridization and mutation as sources of 

genotypic variation in dandelions of North America. She 

found that multiple hybridization events in populations 

(prior to their introduction to North America) were a more 

important source of genotypic variation than mutation in 

populations. 

(d) Illustrations. The morphology of a seedling at the threeleaf 

stage and a mature T. officinale plant are shown in 

Fig. 1. Details of one floret and one cypsela (seed) are 

shown in Fig. 2. A number of internet sites exist which contain 

photos or illustrations of T. officinale including 

http://www.rce.rutgers.edu/weeds/weed.asp?pname= 

dandelion 

http://www.biologie.uni-hamburg.de/b_online/thome/ 

band4/tafel_146.html 

http://clay.agr.okstate.edu/alfalfa/images/weeds/ 

composite/non-thistle.htm 

http://www.agry.purdue.edu/turf/weeds/dandelion/ 

dandelion.htm 

http://elib.cs.berkeley.edu/cgi/img-query?wheregenre=plants&where-taxon=Taraxacum+officinale 

3. Economic Importance 

(a) Detrimental. Taraxacum officinale infests terrestrial 

habitats worldwide and is especially adapted to pastures, 

lawns, orchards, hay fields, roadsides and other areas of 

occasionally disturbed vegetation (Holm et al. 1997). It has 

become a problem weed in golf courses, municipal parks, 

home gardens, athletic fields, agricultural crops, vegetable 

gardens and horticultural crops such as strawberries (Witty 

and Bing 1985; Riddle et al. 1991; Holm et al. 1997). T. 

officinale plants are an aesthetic problem during flowering 

and seed production periods, interrupting turfgrass uniformity 

and density (Riddle et al. 1991). It is an increasing 

problem in annual cereal and oilseed crops in western 

Canada (Derksen and Thomas 1997), and was ranked the 

sixth most important weed occurring in corn, soybean and 

winter wheat fields in southwestern Ontario, being found in 

more than 25% of 593 fields examined (Frick and Thomas 

1992). It was the sixth most abundant weed species in 

reduced and no tillage fields and the tenth most abundant 

species in conventionally tilled fields (Frick and Thomas 

1992). Taraxacum officinale may have been more common 

in fields with reduced or no tillage because its control was 

facilitated by intensive tillage or because the increased crop 

residue in these fields aided in trapping wind-borne seeds 

(Frick and Thomas 1992). The brilliantly coloured inflorescences 

give fields a weedier appearance than is really the 

case (Holm et al. 1997). 

In the USA, corn yields were drastically reduced by 

T. officinale, especially when the previous crop was corn 

rather than soybeans (Hartwig 1990). It has also been reported 

as one of the most dominant weed species in wheat fields 

in Pakistan (Ahmad 1993). When present in dense populations, 

T. officinale can cause slower drying of hay because 

of its high water content, and can be a potential seed source 

for other parts of the farm (Tardif 1997). Doll (1984) found 

that forage from an alfalfa crop with a T. officinale infesta-


tion of 13–31% dry weight required an additional day to dry 

to the same level as forage free of T. officinale. Leaves of T. 

officinale dried faster than stems or ribs and this can cause a 

loss in dry matter yield during mechanical haymaking 

(Isselstein and Ridder 1993). 

Fig. 1. (A) seedling at three-leaf stage (× 

1/2 ); (B) mature plant (× 1/2 ). 

Taraxacum officinale also occurs as a weed in national 

parks (Tyser and Worley 1992) and in peppermint fields in 

the USA (Carda et al. 1992). It may also act as an alternative 

host for boll weevils (Haynes and Smith 1992), cabbage 

looper, yellow-striped armyworm (Dussourd and Denno

1994), green peach aphid (Kaakeh and Hogmire 1991), 

Pseudomonas viridiflava, which causes bacterial streak and 

bulb rot of onion (Gitaitis et al. 1998), and numerous viruses 

(Brcák 1979; Mountain et al. 1983). 


Fig. 2. (A) floret (× 4); (B) cypsela (seed) (× 7). 

Taraxacum officinale is used as a medicinal plant (see 

section 3b), however, overindulgence may render the liver 

inactive and cause various unpleasant symptoms (Jackson 

1982). The pollen of T. officinale has been identified as an


allergen in honey (Helbling and Wuethrich 1987) and can 

cause allergic contact and photoallergic contact dermatitis 

(Mark et al. 1999). Taraxacum officinale inflorescences in 

orchards are perceived as a serious competitor to flowering 

apple and pear trees for honeybee visits, and much time and 

expense is spent mowing to remove them. However, a study 

in Ontario showed that apple pollen accounted for >90% of 

the pollen collected, even when the ratio of dandelion to 

apple inflorescences was 28:1; and mowing had no effect on 

the percentage of pollen collected (Laverty and Hiemstra 

1998). Similarly, a study in Hungary found that T. officinale 

inflorescences were scarcely visited by honeybees compared 

to flowering pear trees (Benedek et al. 1998). 

(b) Beneficial. Taraxacum officinale has been used for medicinal 

purposes for centuries to treat a myriad of conditions 

(Culpeper 1826; Powell 1972), including to improve liver 

function, lower cholesterol, lower blood pressure (Mattern 

1994), decrease body weight in obese patients, treat gall 

bladder ailments (Dalby 1999) and as a diuretic (Rácz- 

Kotilla et al. 1974). Matol Botanical International Ltd. produces 

and distributes a health tonic sold under the brand 

name MATOL in Canada (Km in the USA) that contains 14 

medicinal-plant extracts, including an extract from roots of 

T. officinale (Michaud et al. 1993). Leaves of T. officinale, 

mixed with other plant material, have been used therapeutically 

for liver, kidney, skin and even cancerous diseases 

(Neamtu et al. 1992). Dandelion infusion has a beneficial 

effect on urolithiasis (kidney stones) that can be attributed to 

some disinfectant action, and tentatively, to the presence of 

saponins (Grases et al. 1994). 

The feed value of T. officinale is high, with only trace 

amounts of essential oils and a low amount of tannin that 

might affect quality or palatability (Falkowski et al. 1990). 

The plant can contain as much protein as white clover 

(Bockholt et al. 1995) and is a valuable feed, based on its fat 

and carbohydrate content (Spatz and Baumgartner 1990). 

Bergen et al. (1990) found that T. officinale had protein and 

mineral contents high enough to exceed the established 

requirements for cattle, and that cattle consumed dandelion as 

readily as, or sometimes in preference to, grass pasture. 

However, Falkowski et al. (1990) reported that it was not eaten 

readily by most domestic animals because of its bitterness. 

Taraxacum officinale has been tested as a soil amendment 

for organically grown herbs, but it was not as useful as some 

other weeds (Li 1996). It also possesses allelopathic properties 

and can suppress some fungal pathogens, such as 

Fusarium oxysporum f. sp. radicis-lycopersici Jarvis & 

Shoemaker, and nematodes (Jarvis 1989; Falkowski et al. 

1990; Alvarez et al. 1998). Fresh aboveground material of T. 

officinale lowered population densities of infective, secondstage 

juveniles of the nematode Meloidogyne hapla 

Chitwood and, therefore, increased carrot yield in the greenhouse 

(Alvarez et al. 1998). 

Taraxacum officinale is commonly used as a salad green. 

In Toronto alone, 155 tonnes of leaves (valued at 

Can$595 000.00) were marketed in 1988 and 1989 

(Letchamo and Gosselin 1995). Recently, a program was 

initiated in Québec to introduce organic production of T. 

officinale for commercial processing of the roots (Letchamo 

and Gosselin 1995). Extracts from T. officinale have been 

used in cheese preparation, due to its milk clotting and proteolytic 

properties (Akuzawa and Yokoyama 1988). 

Taraxacum officinale plant parts are used in soups, main 

courses, desserts and beverages, including tea, wine, beer 

and a coffee substitute (using dried roots that have been 

roasted and ground) (Gail 1994; Dalby 1999; Khan 2001). 

The inflorescences are also an excellent source of nectar for 

honey; however, the nectar is more commonly used by beekeepers 

in the brood nest for spring colony build-up (Gail 

1994; Dalby 1999). 

Taraxacum officinale is a good indicator of environmental 

pollution and is often used as a biomonitor because it is 

an abundant, widely distributed plant, and the leaves and 

roots accumulate metals, including As, Br, Cd, Co, Cu, Cr, 

Hg, Mn, Pb, Sb, Se and Zn (Kuleff and Djingova 1984; 

Djingova et al. 1986; Simon et al. 1996). Recently it was 

used to evaluate trace metal bioavailability in abandoned 

industrial sites, community gardens and parks in urban 

Montréal, QC (Marr et al. 1999). With increasing levels of 

pollution, traits such as the length and weight of seeds 

decrease, but the number of seeds increases, as an adaptation 

to survive unfavourable conditions (Savinov 1998). 

Taraxacum officinale is also useful as an experimental 

subject in classroom practical work. As it is very common, 

easily recognizable and perennial, it is easy to obtain and is 

ideal for studying germination, gravitropism, auxin effects, 

water potential measurement, polarity of root sections, morphological 

variation and plant cell structure (Oxlade and 

Clifford 1999) (See also Section 7c). 

(c) Legislation. Taraxacum officinale is listed as a noxious 

weed in Saskatchewan (Anonymous 1984) and in Québec, 

where it is considered noxious when it is found growing on 

roadside verges, along railways and electrical energy transmission 

lines, in ditches and fields, and in unoccupied lots 

(Anonymous 1977). Taraxacum officinale is designated as a 

nuisance weed in Alberta (Anonymous 1991) and is in the 

schedule of weeds that may be declared noxious by the 

Lieutenant Governor in Council in Manitoba (Anonymous 

1981). Taraxacum officinale is not listed in any other 

provincial weed control acts. 

4. Geographical Distribution 

More than 1000 herbarium samples and records were examined 

to determine the distribution of T. officinale in Canada 

and ca. 900 records were included in the final distribution 

map (Fig. 3). The availability of samples and records often 

did not reflect the prevalence of the species within a particular 

area but this is often the case with common species. The 

correct identity of the samples and records was not verified, 

primarily due to the taxonomic uncertainty of many species 

within this genus. Only samples and records that were determined 

as T. officinale were included in the distribution map 

and analysis. 

The geographical distribution of T. officinale in Canada is 

summarized in Fig. 3. Taraxacum officinale has been reported 

from all provinces and territories of Canada, including

the Northwest, Yukon and Nunavut Territories (Rousseau 

1968; Scoggan 1979). This species is widely distributed 

within Canada and records were also found from almost all 

isolated regions, including Sable Island, Anticosti Island, 

Vancouver Island, Queen Charlotte Islands, and Akimiski 

Island (James Bay). 

Taraxacum officinale is distributed within Canada from 

41°42Ń (Ontario) to 64°48Ń (Yukon Territory) latitude, 

and from 49°37´W (Newfoundland) to 139°50´W (Yukon 

Territory) longitude. In Alaska, records were found as far 

north as 67°06Ń latitude, and as far west as 176°45´W longitude. 

Taraxacum officinale is also found in over 60 countries 

worldwide (Holm et al. 1997). 

5. Habitat 

(a) Climatic requirements. Taraxacum officinale can tolerate 

a broad range of climatic conditions (Simon et al. 1996) 


Fig. 3. Canadian distribution of Taraxacum officinale. Information was gathered from specimens and records in the following herbaria: 

ACAD, ALA, APM, CAFB, CAN, DAL, DAO, DAS, LRS, MALA, NFLD, NFO, NSAC, NSPM, OAC, OLDS, PMAE, QFA, QK, QSA, 

SASK, SCFQ, SCS, SSMF, TRT, TRTE, TUP, UBC, UNB, UQTR, WAT, WIN, WINDM, and WLU [herbarium abbreviations as in 

Holmgren et al. (1990), as presented in http://www.nybg.org/bsci/ih/ih.html]. 

and is distributed in almost every temperate and subtropical 

region of the world (Holm et al. 1997). Established T. officinale 

plants are very resistant to drought, while young plants 

are very sensitive and have a limited chance of invading 

coarse-textured or rapidly drying soils (von Hofsten 1954). 

Taraxacum officinale shows a wide range of adaptability to 

light, being able to grow vigorously in full sunlight, or in 

diffused light in the shade of trees or buildings (when leaves 

are usually thinner and more tender) (Longyear 1918). It 

may grow at sea level or up to an elevation of 3350 m, 

where it can be found associating with one or more subalpine 

or alpine native species (Longyear 1918). 

(b) Substratum. Taraxacum officinale can grow in a wide 

range of soils (Simon et al. 1996) but it flourishes best in 

moist, good-quality loam (Jackson 1982). Soil moisture 

determines its local distribution, with well-watered areas of


lawns being especially favourable for its growth (Longyear 

1918). However, it has been recorded pushing up through 

concrete, hanging from eaves troughs of houses, and growing 

from cracks in old stone walls (Jackson 1982). It grows 

in soils ranging in pH from 4.8 to more than 7.6, but does 

not thrive on shallow and drought-sensitive soil (von 

Hofsten 1954, P. B. Cavers, personal communication, 

University of Western Ontario, London, ON). In hilly terrain, 

T. officinale occurs more often on ridges than in hollows 

but this may be due to differential herbivory (e.g., 

slugs, rodents, grasshoppers) on the gradient, rather than differential 

effects of competition (Reader 1992). 

(c) Communities in which the species occurs. Taraxacum 

officinale occurs in lawns, gardens, waste ground, roadsides, 

fields (forage fields such as alfalfa) and their margins, and notill 

crop production systems in agricultural crops (Lovell and 

Rowan 1991; Hamill 1997). Interestingly, it is one of the predominant 

species in black-tailed prairie dog towns in North 

Dakota (Stockrahm et al. 1993) and is the favourite food of 

pocket gophers in Utah, USA (Ellison and Aldous 1952). 

Taraxacum officinale occurs in grassland communities 

and, after renovation, meadows and pastures are often invaded 

rapidly (Haugland 1993). Nitrogen levels had limited 

effects on competition patterns between grass swards and T. 

officinale, but competition among roots affected shoot dry 

weight much more than competition among shoots 

(Haugland 1993). Shading increased leaf length and specific 

leaf area, which made T. officinale less susceptible to competition 

for light (Haugland 1993). Shoot competition reduced 

root dry weight and increased the shoot:root ratio, which, in 

turn, may have reduced plant survival (Haugland 1993). 

Establishment and performance of T. officinale in grass 

vegetation is dependent on the height and cutting frequency 

of the grass (Molgaard 1977). This Danish study found that 

with increasing grass height, the density of T. officinale 

decreased, at least partly due to shading (Molgaard 1977). 

Also, the reproductive morphology of T. officinale in alfalfa 

fields was different, facilitating colonization of open areas, 

compared to the reproductive morphology on undisturbed 

sites with a high density of grass (Welham and Setter 1998). 

6. History 

Many botanists believe that T. officinale originated in 

Greece, or perhaps the Northern Himalayas, and spread 

across temperate areas to Europe and Asia Minor (Richards 

1973; Schmidt 1979; Gail 1994). Taraxacum officinale has 

a fossil record that goes back to glacial and interglacial 

times in Europe (Godwin 1956) and it is thought to have colonized 

the Americas post-Pleistocene via Beringia 

(Richards 1973). Later introductions of T. officinale to 

North America are obscured in conflicting claims (Gail 

1994). The earliest claim is that it arrived on the east coast 

with the Vikings about 1000 AD; others say it first came on 

the Mayflower; while others claim the introduction was by 

later settlers who brought it as a garden plant or a pot herb 

for medicinal purposes (Schmidt 1979; Jackson 1982; Gail 

1994). The earliest recorded observation of T. officinale in 

North America was in the New England area in 1672 

(Rousseau 1968). The Cree, Digger, Apache and Mohican 

Indians soon became aware of its virtues and used it as a 

medicinal herb (Jackson 1982; Dalby 1999). It is likely that 

there have been multiple introductions from many sources 

(Gail 1994). The plant is thought to have spread to the west 

coast with loggers and settlers (Schmidt 1979). The first 

Canadian collection of T. officinale was made in Montréal, 

QC, in 1821, where it was observed as a common species 

(Rousseau 1968). 

7. Growth and Development 

(a) Morphology. Phenotypic variability in T. officinale 

increases its ability to colonize a wide range of habitats. In 

cool or dry weather, or in closely mown lawns, the leaves 

usually spread flat against the surface of the ground to form 

an almost prostrate rosette (Longyear 1918; Lovell and 

Rowan 1991). In warmer weather or in areas where it is 

crowded by taller vegetation, the leaves stand in more or 

less erect tufts (Longyear 1918). The rosette enables it to 

survive mowing, grazing and competition with grasses 

(Baker 1974). The possession of toothed leaves, which 

resemble those of thistles, and the bitter white latex, are 

thought to be adaptations to deter grazing animals 

(Richardson 1985). 

Taraxacum officinale displays a wide range of leaf 

shapes, from a smooth rounded (juvenile) form to a deeply 

incised runcinate (adult) form (Sánchez 1971). The 

length:breadth ratio decreases as the leaf number increases 

(Sánchez 1971) and the ratio and depth of incisions in the 

runcinate form are influenced by light, mediated by the phytochrome 

system (Wassink 1965; Sánchez 1967). Therefore, 

leaf shape can be regulated by light intensity and quality, 

with rounded blades developing at low light energy values 

and runcinate blades developing at high light energy values 

(Sánchez 1967; Slabnik 1981). An increase in light intensity 

increases the degree of lobing and decreases the 

length:breadth ratio (Slabnik 1981). 

The species possesses a deep tap root that can extend 

below the level of competing grass roots (Loomis 1938), 

and make it difficult to remove plants manually (Lovell and 

Rowan 1991). The root system can be widely branched and 

surmounted by a crown, which can divide to form numerous 

(up to 22) crown branches, depending on the degree of 

crowding by other plants and plant age (Roberts 1936). The 

roots are also highly regenerative, capable of producing 

shoots and roots within 1–2 wk from very small segments 

(Longyear 1918; Warmke and Warmke 1950; Mann and 

Cavers 1979). When cut off below the crown, the root usually 

produces several new shoots so that a cluster of new 

plants is formed (Longyear 1918). At the end of the growing 

season, the root shortens and draws the crown slightly 

into the soil, where it is better protected from adverse 

conditions (Longyear 1918). The ease of regeneration is 

reportedly related to the ability of the parenchymatous cells 

of the secondary phloem and xylem in the root to readily 

dedifferentiate and develop into new shoots and roots 

(Higashimura 1986). 

During the development of the inflorescence, the growth 

rate and georesponse of the scape varies (Clifford and

Oxlade 1989). The scape elongates to bloom, then bends 

down close to the ground while the seeds mature, where it 

can escape injury from lawnmowers or grazers (Longyear 

1918; Richardson 1985). When seeds are nearly mature, the 

scape elongates again up to 75 cm, maximizing its height for 

effective dispersal of the wind-blown seeds (Longyear 

1918; Jackson 1982; Richardson 1985). Therefore, the scape 

grows upright (negatively orthogeotropic) when extension 

growth is rapid, as it is prior to flowering and during formation 

of the inflorescence (Oxlade and Clifford 1981). 

However, between these stages, when extension growth is 

minimal and the inflorescence is closed, the scape can grow 

parallel to the ground (diageotropic) for some or most of its 

length (Oxlade and Clifford 1981). The outer tissue layers of 

T. officinale scapes are held in a state of longitudinal tension 

by internal stem tissues, which are held in a reciprocal state 

of compression (Niklas and Paolillo 1998). 

Fasciation has been recorded in T. officinale in two forms, 

confined to the reproductive tissues of the plant (Dekker 

and Dekker 1987). In plants with multiple scapes, the 

central scapes can be fused together to form one broad 

(1–2 cm) scape; or inflorescences (2–4) can be fused at their 

base to form a longitudinal floral structure (Dekker and 

Dekker 1987). 

(b) Perennation. Taraxacum officinale overwinters as seed 

or it retains a reduced basal rosette under snow cover (Cyr 

et al. 1990). 

(c) Physiological data. Taraxacum officinale leaves are rich 

in fibre, potassium, iron, calcium, magnesium, phosphorus, 

vitamins A and C, the B vitamins thiamine and riboflavin, 

and protein (Schmidt 1979; Jackson 1982; Gail 1994). Gail 

(1994) reported that they are also nature’s richest vegetable 

source of β-carotene at 0.84 mg g –1 tissue compared to carrots 

(Daucus carota L.) at 0.61 mg g –1 tissue. They rank 

above broccoli (Brassica oleracea L.) and spinach 

(Spinacia oleracea L.) in overall nutritional value 

(Haytowitz and Matthews 1984), and Minnich (1983) 

ranked them out of all vegetables (including grains, seeds 

and greens) as tied for ninth best, higher than lettuce 

(Lactuca sativa L.). Also, the roots of T. officinale are rich 

in iron, copper and other trace elements (Dwyer 1977). The 

most prominent therapeutic property of T. officinale is the 

diuretic activity, which is based on the high potassium content 

of the plant (Hook et al. 1993). It is superior to other 

diuretics because it reduces the likelihood of hypokalaemia, 

a common side-effect of many diuretics (Houghton 1995). 

The major and trace element content of T. officinale alters 

with growth stage (Müller and Kirchgessner 1972). In a 

Finnish study, the vitamin C content was lowest, while dry 

matter, soluble solids and mineral content were highest in 

late summer (Kuusi et al. 1982). Dandelion mineral content 

was investigated by van der Kley (1956) to assess the suitability 

of this species as feed for livestock. The high 

amounts of protein and β-carotene, favourable mineral composition, 

and low nitrate content throughout the growing 

season in Poland provided a high value feed (Falkowski 

et al. 1990). In UK studies, the availability of these elements 


was equivalent to that in perennial ryegrass (Lolium perenne 

L.), a popular forage species (Wilman and Derrick 1994). 

Taraxacum officinale also had a lower proportion of cell 

walls in dry matter than perennial ryegrass (Derrick et al. 

1993). The true dry matter digestibility was as high as that 

of ryegrass, but the in vivo digestibility was lower (Derrick 

et al. 1993). 

The qualitative and quantitative distribution of 

carotenoids in T. officinale inflorescences did not change, 

regardless of the year, season or location of sampling (Tóth 

and Szabolcs 1970). Pollen of T. officinale contained 

carotenoids, leucoanthocyanidins, flavonols and ascorbic, 

chlorogenic, triterpene, palmitic, stearic, linoleic and 

linolenic acids (Bandyukova et al. 1983). Bandyukova et al. 

(1989) found the amino acid composition of pollen to be 

similar to that of pollen of other plants. The pollen contained 

a low concentration of ct-ABA (cis trans abscisic acid) and 

a high concentration of proline, which serves several functions 

including drought and cold resistance (Lipp 1991). 

Callus development, and leaf and root formation, 

occurred in tissue cultures isolated from secondary thickened 

roots of T. officinale (Bowes 1970). Tissue cultures 

produced the same spectrum of compounds as intact plants 

and, in actively growing suspension cultures, volatile 

metabolites with an apple-like odour (Hook et al. 1991; 

Hook 1994). The application of nitrogen (as potassium 

nitrate) promoted the growth of roots and shoots (Khan 

1975). Auxins and cytokinins are also likely to be involved 

in the hormonal control of regeneration and are necessary 

for growth and organogenesis (Booth and 

Satchuthananthavale 1974a, b). In a British laboratory 

study, the addition of gibberellin to T. officinale leaf discs 

retarded their senescence and delayed the decline in levels 

of chlorophyll, protein and RNA (Fletcher and Osborne 

1966). The level of endogenous gibberellins in leaf tissue 

was high during leaf growth and expansion but declined 

progressively during senescence (Fletcher et al. 1969). 

Aging of leaves was associated with a deficiency of endogenous 

gibberellins (Fletcher et al. 1969). 

Undifferentiated cultured cells of T. officinale produced 

oleanolic and ursolic acids as major triterpenoids, in addition 

to triterpenols composed mainly of α- and β-amyrins 

(Akashi et al. 1994). Regenerated and wild plants contained 

additional triterpenols, including taraxasterol and lupeol, but 

negligible quantities of triterpene acids (Akashi et al. 1994). 

High squalene synthase activity was detected at the late logarithmic 

growth stage of suspension-cultured cells that produced 

triterpenoids, since squalene is an intermediate in 

sterol and cyclic triterpene biosynthesis (Komine et al. 

1996). Taraxacum officinale accumulated the serine proteinase 

taraxalisin in latex but this latex did not contain cardenolides, 

which are cardioactive compounds found in the 

latex of some other weeds (Sady and Seiber 1991; 

Rudenskaya et al. 1998). 

Taraxacum officinale is a C 3 species (Kemp et al. 1977). 

In US studies, plants from different altitudes showed no significant 

differences in enzyme activity, net photosynthesis, 

dark respiration, photorespiration, transpiration rates or temperature 

responses of gas exchange (Kemp et al. 1977;


Oulton et al. 1979). This is in disagreement with earlier US 

reports, which indicated that there were differences in the 

photosynthetic Hill reaction and enzyme activity among the 

same altitudinally diverse populations (May and Villarreal 

1974; May 1976). Activity of the enzyme invertase, which 

was only present in the petiole and central midrib of the 

developing leaf, was correlated with leaf growth rate and its 

level was controlled by light (Slabnik 1981). 

Various chemicals and cellular structures play roles in the 

geotropic behaviour of T. officinale. UK studies showed that 

elevated levels of endogenous ethylene were associated with 

the diageotropic behaviour and reduced extension growth 

after flowering (Clifford and Oxlade 1989). There were significant 

differences in indol-3yl-acetic acid (IAA) levels 

across the scape after geostimulation, indicating a role for 

auxin in geotropism (Clifford et al. 1985). In an earlier 

British study, Clifford and Barclay (1980) showed that amyloplasts 

(colourless plastids that form starch granules) in 

the cells of scapes sediment much faster than previously 

reported and were involved in the initiation of geotropism in 

T. officinale. 

In other Canadian studies, it was found that amino acids 

accumulated in the roots as fall senescence progressed in the 

aerial parts of the plant, and declined in spring when 

regrowth occurred, with large fluctuations in the amides 

asparagine and glutamine (Cyr and Bewley 1990a). An 

18 kDa protein increased in T. officinale roots during the fall 

months, suggesting that it has a role as a storage compound 

(Cyr and Bewley 1990b). The same protein was also found in 

inflorescences, the stem and seeds (Cyr and Bewley 1990b). 

Plants exposed to elevated levels of CO 2 grew faster, 

exhibited more deeply incised leaf margins and had relatively 

more slender leaf laminae than those exposed to 

ambient levels (Thomas and Bazzaz 1996; Staddon et al. 

1999). These effects were most pronounced when T. officinale 

plants were grown individually, but detectable differences 

were also found in plants grown at high density 

(Thomas and Bazzaz 1996). This supports the hypothesis 

that leaf carbohydrate levels play an important role in regulating 

heteroblastic leaf development, although elevated 

CO 2 may also affect leaf development through direct hormonal 

interactions or increased leaf water potential 

(Thomas and Bazzaz 1996). 

A US study showed that the leaf size of T. officinale 

plants decreased linearly with increasing elevation and a 

corresponding decline in nocturnal infrared irradiation from 

the sky (Jordan and Smith 1995). Differences in plant leaf 

structure and physiology traditionally associated with daytime 

sun exposure may also be influenced by nighttime sky 

exposure and susceptibility to frost (Jordan and Smith 1995). 

Red light and far-red light influenced the water exchange of 

epidermal cells of T. officinale and phytochrome appeared to 

be involved (Carceller and Sánchez 1972). 

Environmental factors, such as temperature, photoperiod 

and rainfall, were studied in Finland for their effect on the 

bitterness of T. officinale (Kuusi and Autio 1985). It was 

found that increasing temperature and photoperiod and 

decreasing rainfall were correlated with an increase in bitterness. 

However, morphological characters such as leaf 

shape, main nerve breadth and colour of petiole base were 

not correlated with bitterness (Kuusi and Autio 1985). 

Growth phase and season had a strong influence on bitterness, 

with plants being less bitter in spring before flowering 

than in late summer (Kuusi and Autio 1985). Bitterness in 

leaves was caused by sesquiterpene lactones, such as taraxinic 

acid and its glucoside, as well as triterpenoids, such as 

cycloartenol (Houghton 1995). Kuusi et al. (1985) identified 

four bitter compounds: p-hydroxyphenylacetic acid, β-sitosterol, 

11,13-dihydrotaraxine acid 1’-O-β-D-glucopyranoside 

and taraxine acid 1’-O-β-D-glucopyranoside [also 

identified as an allergen (von Hausen 1982)]. The following 

triterpene alcohols have been isolated from roots of T. officinale: 

taraxol, taraxerol, ψ-taraxasterol, taraxasterol, βamyrin, 

stigmasterol and β-sitosterol; along with phenolic 

acids related to caffeic acid and β-fructofuranosidases 

(Burrowes and Simpson 1938; Rutherford and Deacon 

1972; Houghton 1995). Caffeoyltartaric acids, cinnamic 

acids, coumarins and flavonoids have also been isolated 

from T. officinale tissues, including leaves (Williams et al. 

1996; Budzianowski 1997). 

A UK study showed that sterol levels in leaves of T. officinale 

fluctuated with season, probably due to temperature 

(Westerman and Roddick 1981). Free 4-demethyl sterols 

were maximal during the winter months and levels were 

correlated negatively with sunshine and temperature 

(Westerman and Roddick 1981). Sitosterol ester and 

cycloartenol ester showed the opposite response, with levels 

correlating positively with sunshine and temperature 

(Westerman and Roddick 1981). The scapes contained predominantly 

β-sitosterol and β-amyrin (Aexel et al. 1967). 

Taraxacum officinale possesses allelopathic properties 

that can reduce germination of other plant species 

(Falkowski et al. 1990). In addition, phenolic compounds 

produced by T. officinale are considered responsible for 

allelopathic biological control of Fusarium oxysporum f. sp. 

radicis-lycopersici in greenhouse tomato plantings in 

Canadian experiments (Kasenberg and Traquair 1988). 

Satisfactory control of this pathogen was achieved when 

residues of T. officinale were incorporated into sterilized 

greenhouse soil. The mode of action is unknown but it may 

act directly by secretion of allelochemicals or promotion of 

antagonistic microflora (Jarvis 1989). 

An anti-fungal toxin was inducibly produced by T. officinale 

leaves treated with cupric chloride but production was 

depressed under oxygen deficient conditions (Mizutani 

1989). This compound was identical to lettucenin A, which 

has been isolated from lettuce infected with Pseudomonas 

cichorii (Takasugi et al. 1985). Lettucenin A is a stressinduced 

antifungal sesquiterpenoid that was present in sufficient 

quantity to suppress invasion of a pathogen in vivo 

(Hanawa et al. 1995). It was found that lettucenin A production 

started at an early stage of fungal infection, before 

the appearance of symptoms, and ended soon after the death 

of the pathogen (Hanawa et al. 1995). 

Carbohydrate and nitrogen reserves in the roots of T. 

officinale fluctuate with the season (Loomis 1938). The 

roots remained viable during the winter and acted as a 

source of nutrients to facilitate the resumption of growth in

early spring (Cyr et al. 1990). Fructans, storage carbohydrates 

such as inulin and inulo-n-ose, were synthesized in 

roots by the enzyme fructan-fructan fructosyl transferase 

(Lüscher et al. 1993; Ernst et al. 1996). This synthesis of 

inulin was practically unaffected by the height of competing 

grass vegetation (Molgaard 1977). High inulin content in 

roots resulted in high nitrogenase activity (Vlassek and Jain 

1976), which could enrich the soil with nitrogen through 

asymbiotic nitrogen fixers such as Azotobacter and 

Clostridium species (Vlassek and Jain 1978). Fructan 

hydrolysis occurred during late autumn and provided simple 

sugars as a readily accessible carbon pool (Cyr et al. 1990). 

Nitrates, free amino acids and soluble proteins were important 

vehicles for nitrogen storage (Cyr et al. 1990). Storage 

reserves remained at peak levels throughout winter and 

declined prior to the resumption of growth in spring, when 

inulin was metabolized to provide a high content of mobile 

fructose and sucrose to enable extensive vegetative growth 

and flowering (Molgaard 1977; Cyr et al. 1990). At the time 

of fruiting, nitrogen reserves were at their lowest concentration 

(Loomis 1938). Toward the end of summer, these 

reserves were restored and the cycle began again 

(Rutherford and Deacon 1974). 

Taraxacum officinale was identified as a valuable source 

of the essential linolenic acid, apigenin-7-glucoside, 

lecithin, and cholin (Houghton 1995; Letchamo and 

Gosselin 1995). Unsaturated hydroxy fatty acids such as 

linolenic acid are important in the chilling-resistant properties 

of T. officinale (Imai et al. 1995). 

(d) Phenology. Generally, during the first season of growth, 

T. officinale seedlings produce only leaves, usually in 

rosettes (Longyear 1918). In the spring of the second season, 

and each season thereafter, inflorescences are produced 

(Longyear 1918). However, under favourable conditions, 

some seedlings can bloom in their first year (von Hofsten 

1954; Listowski and Jackowska 1965). The first bud may 

appear at various times and cannot be correlated to leaf 

index, although the plant has to have formed at least 20 

leaves and enlarged its tap root to store the required energy 

(Listowski and Jackowska 1965; Solbrig 1971). The time of 

first flowering is partly dependent on the surrounding plant 

community and, in undisturbed communities, a plant may 

not flower until its fourth season (Gorchakovskii and 

Abramchuk 1996). 

In T. officinale, flowering occurs over a wide range of 

photoperiods and light intensities. Studies on seasonal variation 

in flowering of T. officinale in Kentucky, showed that 

plants flowered throughout the year, with most plants flowering 

in April when the average daily air temperature was 

16°C and day length was about 13 h. A secondary peak 

occurred in September and October, with an average of 

21°C and 12–13 h day length (Gray et al. 1973). Therefore, 

T. officinale can be classified as a day-neutral plant 

(Listowski and Jackowska 1965; Gray et al. 1973), although 

Solbrig (1971) classified it as a short-day plant due to limited 

flowering during long summer days. Individual plants 

that bloom in spring may also bloom again in fall (Listowski 

and Jackowska 1965). Bud formation in these plants occurs 


during a period of decreasing daylight, when the differentiation 

of new leaves is limited and existing leaves show 

symptoms of premature aging (Listowski and Jackowska 

1965). The time course of the main spring flowering period 

may vary in different years, partly due to differences in 

microclimate, such as the amount of sunshine and soil temperature 

(von Hofsten 1954; Sterk and Luteijn 1984). The 

number of times the inflorescences open and close, the 

length of time that the inflorescences remain open each day, 

and the length of time that the inflorescences remain closed 

before opening into mature heads, vary with time of year 

(Gray et al. 1973). 

The development of buds requires approximately 1 wk 

(Solbrig 1971). A scape is formed between the base of 

the bud and the tip of the shoot in about 48 h (Solbrig 1971). 

On average, inflorescences open during 2 or 3 successive 

days, after which they remain closed until the seeds mature 

(Longyear 1918; Gray et al. 1973). The scape and the 

inflorescence flatten to the ground and, after a couple of 

days, the scape straightens and the involucral bracts surrounding 

the closed inflorescence open to reveal seeds 

(Solbrig 1971). The time required from the first day of 

blooming until the seeds ripen and the bracts open to release 

them, is about 9–12 d (Longyear 1918; Beach 1939; Gray 

et al. 1973). 

A study in Japan showed that at low temperatures, inflorescences 

opened in response to increasing temperature 

(thermonasty), whereas at higher temperatures, they opened 

in response to light (photonasty) (Tanaka et al. 1988). The 

minimum temperature for photonastic opening was 13°C 

and inflorescences remained open for 13–14 h (Tanaka et al. 

1988). At temperatures of 13–18°C, plants were in full 

bloom and this was most favourable for nectar secretion, 

pollen production and bee activity (Kremer 1950). In 

Michigan, USA, inflorescences were reported to close when 

the temperature was over 21°C or during adverse weather, 

and could remain closed for several days and then re-open 

when climatic conditions were favourable (Kremer 1950). 

Once closed, however, they did not open again on the same 

day (Kremer 1950). 

Seeds produced in the spring during the peak flowering 

period mostly emerged that same spring or did not emerge 

at all (Collins 2000). However, seeds produced at other 

times during the year produced seedlings throughout the 

year. Seedlings produced in the fall produced seeds in the 

spring of the following year. Chepil (1946) found that 

seedlings emerged in most months of the year in Canada and 

for up to 4 yr after sowing. Collins (2000) collected ripe, 

viable seeds from a single population on the University of 

Western Ontario campus, London, ON, on the following 

dates in 1999: 1, 17, 27 May; 10 June; 20 August; 14, 21 

September; 4, 20 October; 5, 22 November; and 13 

December. At least 58% of the seeds collected on each date 

germinated. P. Cavers (personal communication, University 

of Western Ontario, London, ON) has collected ripe seeds in 

every month of the year, but not every month in a single 

year. He concluded that if there is a January or February 

thaw that lasts for at least a week, then flowering and seed 

production can occur.


The survival and regeneration of root fragments vary seasonally 

(Mann and Cavers 1979). Minimum survival of 

fragments occurred at the time of maximum flowering of the 

source plants and maximum survival of fragments occurred 

in the second growing season (Mann and Cavers 1979). 

(e) Mycorrhiza. Taraxacum officinale forms mycorrhizal 

associations (Truszkowska 1951; Hawker et al. 1957). Two 

vesicular-arbuscular mycorrhizal fungi, Glomus mosseae 

(Nicol. & Gerd.) (Gange et al. 1994) and Pythium ultimum 

Trow. (Hawker et al. 1957), have been reported on T. officinale. 

Infection by G. mosseae conferred some degree of 

resistance in T. officinale roots to larvae of the black vine 

weevil Otiorhynchus sulcatus (Fab.) (Gange et al 1994). 

There have been some recent studies on the mycorrhizal 

interactions of T. officinale, including the effect of elevated 

CO 2 levels on mycorrhizal function (Staddon et al. 1999); 

the effect of non-host and host plants on mycorrhizal colonization 

(Fontenla et al. 1999); and the effect of T. officinale 

on mycorrhiza inoculum potential, soil aggregation and 

yield of maize (Kabir and Koide 2000). 

8. Reproduction 

(a) Floral biology. As T. officinale is an apomict (the embryo 

develops without fertilization) and a triploid of hybrid origin, 

most pollen grains are abortive and sterile, and cannot form 

pollen tubes (Solbrig 1971; Jenniskens 1984). Generally, in 

the Asteraceae, ligulate or ray-florets are sterile, and tubular 

or disc-florets are fertile. However, in T. officinale, there is 

no distinction between ray- and disc-florets, either in appearance 

or function, with all florets being ligulate and equally 

fertile (Roberts 1936). The ligulate florets are surrounded by 

inner and outer involucral bracts that close at night, in overcast 

weather, when the relative humidity is above 97% or 

when the temperature is less than 9.4°C. Opening of the 

inflorescences is inhibited by rain and accelerated by high 

light intensity (Percival 1955; Jenniskens et al. 1984). 

In the Peace River region of Alberta, Szabo (1984) found 

an average daily production of 59.2 inflorescences m –2 , 

which is equivalent to 592 700 inflorescences ha –1 d –1 and, 

over a 25-d blooming period, represented a potential production 

of 14 792 500 inflorescences ha –1 . On a sunny day, 

inflorescences opened between 0800 and 0900, reached a 

peak at 1100 to 1200 and closed gradually from 1500 to 

2100; but the whole period was shorter on dull days since 

high light intensity accelerates inflorescence opening 

(Percival 1955, Szabo 1984). A UK study found that T. 

officinale presented its pollen from 0900 to 1500, with the 

peak period from 1000 to 1100 (Percival 1955). Most inflorescences 

(89%) opened for 2 consecutive days, some (7%) 

for 1 d and some (4%) for 3 d (Szabo 1984). Quantity and 

concentration of nectar were significantly higher in inflorescences 

2 d old than in those 1 d old (Szabo 1984). Larger 

inflorescences produced more nectar, and the nectar-sugar 

concentration and sugar value increased with increasing 

temperature (Szabo 1984). High nectar-foraging activity by 

honeybees coincided with peak nectar-sugar production 

(Szabo 1984), and anthers dehisced over a period of 1–7 d 

(Percival 1955). 

(b) Seed production and dispersal. Although stamens 

and pistils are present and pollen is produced regularly, 

the seed of T. officinale develops without fertilization 

(Roberts 1936). Originally, it was thought that 

seeds were primarily produced by allogamy, and insects 

such as honeybees and flies were pollinators (Longyear 

1918). However, it has been suggested by UK investigators 

that insect visitors, attracted by the bright yellow 

inflorescences, may be needed to trigger seed set (Williams 

et al. 1996). In a heavily infested area in Canada, the 

average number of seeds produced by T. officinale was 

60 000 m –2 , equivalent to about 600 000 000 seeds ha –1 

(Roberts 1936). Under near optimal conditions, the number 

of inflorescences/plant ranged from 48 to 146, with an 

average of 93, while the number of seeds/inflorescence 

ranged from 130 to 412, with an average of 252 (Roberts 

1936). This provides an average of 23 436 seeds/plant 

(Roberts 1936). 

In UK studies on the reproductive success of T. officinale, 

Bostock and Benton (1979) found that of 185.5 ovules 

produced/inflorescence, 181.7 seeds were produced, and 

178.1 were dispersed. As well, an average of 12.2 inflorescences/plant 

were observed, resulting in approximately 

2170 seeds/plant being produced during the growing 

season. Ford (1981b) found that the number of inflorescences/plant, 

number of seeds/inflorescence and, therefore, 

the number of seeds/plant varied with the habitat in which 

Taraxacum agamospecies were found. The number of inflorescences/plant 

was 7.7 for plants on denuded roadsides, 1.7 

for plants on non-denuded roadsides, and only 0.6 for plants 

in upland sites. Similarly, the number of seeds/inflorescence 

was 151 for plants growing in denuded roadside sites, as 

compared to 119 in non-denuded roadside sites, and only 62 

in upland sites. Similarly, a US study found that the number 

of inflorescences/plant and florets/inflorescence depended 

on the size and vigour of the plant (Longyear 1918). Small 

stunted plants growing in dry soil may produce only a single 

inflorescence with 30 florets/inflorescence; while large 

clumps of plants along roadsides may produce 50 or more 

inflorescences at once with more than 200 florets/inflorescence 

(Longyear 1918). 

After flowering, T. officinale scapes elongate significantly, 

allowing enhanced wind dispersal of seeds (Radosevich 

and Holt 1984). The seeds have pappi that further aid in dispersal 

by wind (Lovell and Rowan 1991). The seed settling 

velocity may be a useful surrogate for the measurement of 

dispersal ability (Andersen 1992) and the average settling 

velocity of seed-pappus units of T. officinale is 2.37 km h –1 

(Andersen 1993). Sheldon and Burrows (1973) found that 

the distance travelled by seed-pappus units of T. officinale 

increased with increasing wind speed. Wind speeds of 5.47, 

10.94, and 16.41 km h –1 resulted in distances travelled of 

0.76, 1.52, and 2.27 m, respectively. Von Hofsten (1954) 

estimated the dissemination distance of seeds was 200–500 

m. Seeds are also dispersed in the excreta of animals such as 

cattle, horses and birds (Salisbury 1961), and by water, 

especially via irrigation ditches (Salisbury 1961; 

Radosevich and Holt 1984). Seeds can survive in water for 

up to 9 months (Comes et al. 1978).

Collins (2000) found that the mean mass (mg) per seed in 

the UWO collection ranged from 0.33 mg in an August collection 

to 0.68 mg in a late October collection. At the peak 

of flowering in May, it ranged between 0.43 and 0.49 mg. 

The seeds produced in late October and early November 

were significantly (P = 0.05) heavier than those produced at 

other times of the year. UK reports of seed weights vary, 

with Salisbury (1961) stating an average weight of 0.8 mg, 

Bostock (1978) reporting an average seed weight of 0.583 

mg, while Sheldon (1974) reported the average seed 

weighed 0.0549 mg; one-tenth as much as in any other 

report. Also, the average seed was reported as 10.25 mm in 

length, with a pappus diameter is 6.94 mm (Sheldon 1974). 

(c) Seed banks, seed viability and germination. Very large populations 

of T. officinale seeds can be found in soil. For example, 

in the UK, Champness and Morris (1948) found 1 575 000 

seeds ha –1 in the top 13 cm of soil in a grassland area, and 

2 350 000 seeds ha –1 in the top 18 cm of an arable field. 

At least 7 d must elapse after the opening of the inflorescence 

before most seeds of T. officinale are mature enough 

to germinate (Longyear 1918). Therefore, if all inflorescences, 

including those that have closed to ripen the seeds, 

are removed from the plant (e.g., by mowing), the germination 

of seeds from the dried inflorescences that have ripened 

after cutting is only 13% (Longyear 1918; Roberts 1936). 

Fully mature seeds of T. officinale lack primary dormancy 

and are able to germinate almost as soon as they leave the 

plant (Longyear 1918; Martinková and Honĕk 1997). 

However, the proximity of the seeds to each other influences 

germination. In a US study, seeds placed singly or in groups 

of 5, 10 or 25 had germination percentages of 68, 64, 54 and 

41%, respectively. This significant decrease in germination 

with increasing density may be a population-regulating 

mechanism (Linhart 1976). 

The germination capacity of T. officinale seeds is generally 

80–90% (Falkowski et al. 1989), and Martinková and 

Honĕk (1997) reported 94% germination on moist filter 

paper, 28 d after collection. Most seeds germinate within 

1.5 mo after dispersal (Ogawa 1978). However, von Hofsten 

[quoted by King (1966)] estimated that, of 10 000–20 000 

seeds m –2 dispersed into a meadow, only 50–125 would 

establish successfully. Germination is impaired after passage 

through the digestive tracts of cattle, with germination 

of 52%, 31% and 22% after retention in faeces for 5 h, 24 h 

and 48 h, respectively (Falkowski et al. 1989, 1990). 

Germination is also influenced by individual seed weight 

(Tweney and Mogie 1999). There is variation in the weight 

of seeds produced in a single inflorescence and the heavier 

seeds have a greater probability of germination (Tweney 

and Mogie 1999). 

Seeds of T. officinale germinate over a wide range of temperatures, 

from 5–35°C (Mezynski and Cole 1974; 

Washitani 1984), with less germination at higher temperatures 

(Martinková and Honĕk 1997). Most reports indicate 

that seeds of T. officinale germinate best under alternating 

temperatures and light. Collins (2000) found 85–94% of 

seeds, from two populations from London, ON, germinated 

under the following regimes: 15°C/5°C with 9 h light, 


25°C/10°C with 14 h light, 35°C/20°C with 15 h light and 

25°C/10°C in total darkness. However, other temperature 

regimes in total darkness led to reduced germination, with 

only 75% at 35°C/20°C and 43% at 15°C/5°C. Cross (1931) 

found 75–76% of seeds, collected from Ottawa, ON, germinated 

in alternating temperatures of 30°C/20°C, while only 

60–65% germinated at a constant temperature of 18–20°C. 

Mezynski and Cole (1974) reported maximum germination 

of fresh seeds, collected from Maryland, USA, at an alternating 

temperature of 20°C for 16 h and 10°C for 8 h (while 

seeds stored for 30 d germinated best at 20°C/15°C). 

Maguire and Overland (1959) found that 92% of seeds, collected 

from Washington State, USA, germinated at alternating 

temperatures (30°C/20°C) in alternating light and 

darkness, but when kept in darkness, there was only 72% 

germination. Also, at a constant temperature of 15°C in 

dark, only 4% germination was recorded, but when alternating 

light and dark was added to the same constant temperature, 

96% germination was observed. Two British studies 

(Thompson 1989; Williams 1983) reported similar results. 

Seed germination was greater, faster and more uniform in 

light than in dark (Isselstein 1992; Letchamo and Gosselin 

1996). In a Swedish study, Noronha et al. (1997) used cold, 

dark stratification to show that seeds of T. officinale have an 

inducible light requirement for germination. Ecologically, 

this inducible light requirement is important for preventing 

the germination of buried seeds in conditions unfavourable 

to seedling development (Noronha et al. 1997). 

There are varying reports of the viability of seeds of T. 

officinale after storage. Following burial of T. officinale 

seeds for varying time periods, a small number of seeds 

(1%) were still viable for up to 9 yr after burial (Burnside 

et al. 1996). Typically, 1–6% of T. officinale seeds remained 

viable 4 yr after burial in soil, and soil storage for 5 yr or 

longer resulted in little detectable viability (Chepil 1946; 

Roberts and Neilson 1981). Seeds remained viable longer in 

the soil (up to 20–30 yr) than when dry-stored indoors (von 

Hofsten 1954). Depth of seed burial was negatively correlated 

to establishment success (Bostock and Benton 1983). 

Storage of seeds at room temperature decreased seed viability, 

compared to storage at 4°C (Letchamo and Gosselin 

1996). Mezynski and Cole (1974) reported that percentage 

germination decreased during 30 d storage of seeds at –15°C 

or 22°C, compared to fresh seeds. Al-Hially (1991) found 

that the rate of germination increased after 90 d storage. 

The position of T. officinale seeds affects germination, 

with greatest germination occurring when there is good contact 

between the substrate and the scar of attachment of the 

seed, allowing water uptake (Sheldon 1974). The hygroscopic 

pappus can move to alter the seed position as humidity 

changes and, in high humidity, the pappus closes 

hygroscopically (Sheldon 1974). The backward-pointing 

hairs and teeth of the seed may play a role in firmly anchoring 

it during seedling establishment (Sheldon 1974). 

Increasing soil compaction decreases seed germination, 

radicle penetration and seedling establishment, partly due to 

removal of microsites (Sheldon 1974). 

The endosperm of T. officinale is cellular and the uninucleate 

cells have meagre cytoplasm. At the globular stage of


the embryo, the endosperm shows endospermous haustoria 

at its middle and chalazal portions, which perhaps act to 

draw nourishment from the adjoining tissue to cope with the 

increasing nutritional need of the growing embryo, leading 

to increased seed set (Sood and Sood 1992). 

(d) Vegetative reproduction. The regenerative capacity of T. 

officinale roots has been examined by Naylor (1941) and 

Khan (1973). Vegetative propagule weight was positively 

correlated to establishment success (Bostock and Benton 

1983). Root segments that were 1.25 mm in diameter had to 

be at least 6–10 mm in length to regenerate, and segments as 

short as 2 mm could regenerate only if they were more than 

4 mm in diameter (Warmke and Warmke 1950). The minimum 

length for shoot regeneration was 1.5 mm and for root 

regeneration 2 mm (Khan 1969). More shoots and roots 

regenerated from longer root segments than from shorter 

ones (Khan 1969). Regenerative capacity decreased as fragment 

volume decreased (down the length of the root) (Mann 

and Cavers 1979). Planting cuttings in an inverted or horizontal 

plane, rather than the normal planting orientation 

resulted in a decline in regeneration and survival, and an 

increase in regeneration time (Mann and Cavers 1979). 

Planting depth did not consistently influence regenerative 

capacity or timing (Mann and Cavers 1979). Root fragments 

were highly vigorous and capable of producing new plants 

even when covered by 5–10 cm of soil (Falkowski et al. 

1989, 1990). This may be due to their high sugar content 

(~11% of dry matter) (Falkowski et al. 1990). 

9. Hybrids 

Although sexual reproduction is rare or absent in North 

America (Solbrig and Simpson 1974), natural hybrids have 

been reported to occur between T. officinale and T. platycarpum 

in Japan (Watanabe et al. 1997). More than 90% of 

the plants classified as T. officinale had alleles introduced 

from T. platycarpum and were morphologically intermediate 

between the two species with respect to the number of 

marginal hairs in the outer involucral bract, the length of 

corniculate appendages on the outer involucral bract, and 

the size of the seed (Watanabe et al. 1997). 

10. Population Dynamics 

In a study in West Virginia, the finite rate of increase for an 

entire population was largest in fall and declined throughout 

the rest of the year (Vavrek et al. 1997). The age of T. officinale 

plants can be determined by counting the annual 

growth-rings in the principal roots and plants that are 10–13 

yr old are common (Roberts 1936; von Hofsten 1954). 

Reader (1991a) found that a significantly greater number of 

seedlings emerged on ridges than in hollows in vegetated 

plots, but the experimental removal of ground cover 

increased seedling emergence more in hollows than on 

ridges. Genetically variable individuals of T. officinale, 

known as biotypes, have been identified by their polymorphic 

isozyme patterns. Some biotypes of T. officinale are 

able to outcompete others under certain conditions (Solbrig 

and Simpson 1977). For example, two biotypes grown in 

garden plots were left undisturbed, or subjected to artificial 

disturbance by defoliation or removal of the entire plant by 

tilling (Solbrig and Simpson 1977). In undisturbed plots, 

biotype D accounted for 85% of the plants whereas in disturbed 

plots, biotype D only accounted for 7–9% of the 

plants (Solbrig and Simpson 1977). These population differences 

were a direct response to differences in disturbance 

(Solbrig and Simpson 1974). 

The strong competitive ability of T. officinale is due to 

several properties, including the tap root, which penetrates 

more deeply to reach moisture and nutrients than roots of 

most other plants (Jackson 1982). In addition, plants release 

ethylene, which can inhibit the growth of other plants nearby 

(Dwyer 1977; Jackson 1982). The variable growth habit 

of T. officinale, from thick, wide-spreading rosettes of 

leaves that suppress plants, to erect elongated leaves among 

denser growth, is of competitive advantage (Jackson 1982). 

Developing seed heads droop towards the ground where 

they are protected and seeds are formed without the need for 

fertilization (Jackson 1982). Finally, each inflorescence 

releases hundreds of seeds, which are effectively wind-dispersed 

due to the pappi (Jackson 1982). Seed burial experiments 

established that seedlings of T. officinale emerge 

nearly year-round, peaking in May and again in September, 

with this pattern continuing for up to 3 yr after planting 

(Chepil 1946; Roberts and Neilson 1981). 

The effect of asexual reproduction is to produce offspring 

that are genetically identical to the parent plant (Solbrig 

1971). The ability of dandelion to adapt to different ecological 

niches suggests that T. officinale has a general-purpose 

genotype as well as phenotypic plasticity, with a wide environmental 

tolerance and some adaptation to a wide range of 

biotic and abiotic factors (Solbrig 1971; Baker 1991). 

Taraxacum officinale can be successful as a colonizer and as 

an inhabitant of closed grassland (Baker 1991). Solbrig 

(1971) described genotypes favouring the colonizing phase 

as “r-selected”, emphasizing seed production, and genotypes 

favouring the inhabiting phase as “K-selected”, 

emphasizing competitive ability under different environmental 

conditions. Taraxacum officinale plants are basically 

r-strategists (Gadgil and Solbrig 1972). However, Ford 

(1981b) suggested that the measures of r and K characteristics 

are dependent upon the sites in which these characteristics 

are measured. 

11. Response to Herbicides and Other Chemicals 

Phenoxyacetic acid herbicides, such as 2,4-D and mecoprop, 

or the benzoic acid dicamba, or combination products 

of all three such as “Killex”, are used for chemical control 

of T. officinale in turf (Anonymous 1997). As early as 1944, 

experiments showed that 2,4-D killed T. officinale in lawns 

within 3 wk of application, leaving the grass unharmed 

(Peterson 1967). In Ontario, optimum control was obtained 

with 2,4-D applications in spring in combination with spudding 

(root cutting and shoot removal) (Mann 1981). 

Taraxacum officinale has been classified as intermediate in 

susceptibility to 2,4-D, due to tolerance by older or established 

plants, but it is susceptible in the seedling stage, 

based on the sorption capacity of the cuticle membrane 

(Baker and Bukovac 1971). The growth-regulating proper-

ties of 2,4-D are thought to cause the major herbicidal 

effects, including cell elongation, epinasty and hypertrophy, 

but the precise mode of action of 2,4-D is still unknown 

(Sterling and Hall 1997). The selectivity of 2,4-D toward 

dicotyledonous plants is based on differences in plant morphology, 

and the rate of herbicide translocation and metabolism 

between mono- and dicotyledonous plants (Hagin 

et al. 1970; Devine et al. 1993). 

In creeping red fescue grown for seed in Alberta, various 

mixtures of herbicides were used to control T. officinale 

(Darwent and Lefkovitch 1995). In 94–100% of trials, 

greater than 80% control (percent reduction in biomass) of 

T. officinale was achieved by applying metsulfuron at 4.5 g 

ha –1 , either alone or in combination with each of the 

graminicides sethoxydim (at 500 g ha –1 ) or fluazifop-P 

(at 250 g ha –1 ). A combination treatment of dicamba (at 

280 g ha –1 ) and 2,4-D (at 560 g ha –1 ) provided greater than 

80% control of T. officinale in only 25% of trials. However, 

tank-mixing sethoxydim (at 500 g ha –1 ) or fluazifop-P (at 

250 g ha –1 ) improved the efficacy of the dicamba/2,4-D 

combination, resulting in greater than 80% control of T. 

officinale in 62% and 71% of trials, respectively (Darwent 

and Lefkovitch 1995). The enhanced control from the addition 

of the graminicides to the dicamba plus 2,4-D combination 

is probably due to the effect of surfactants that were 

added to the tank-mix. 

Several herbicides are effective at controlling T. officinale 

in alfalfa or other forage legumes, yet they are not 

registered or recommended in Canada. Moyer et al. 

(1990) reported that annual applications of hexazinone 

(1.0 kg ha –1 ) and chlorsulfuron (0.01 kg ha –1 ) maintained 

almost complete control of T. officinale in alfalfa (Medicago 

sativa L.) and sainfoin (Onobrychis viciaefolia Scop.) 

in Alberta, where control was measured as the reduction 

in dry matter yield. In a study in Saskatchewan 

by Waddington (1980), the herbicides dichlobenil, terbacil, 

and simazine were each applied annually over 3 or 4 yr 

for control of T. officinale. Dichlobenil applied at 

2.2 kg ha –1 resulted in 100% reduction in the T. officinale 

population by spring of the fifth growing season. Similarly, 

terbacil applied at 1.1 kg ha –1 resulted in 96% reduction 

in the T. officinale population by the spring of the fifth 

year. However, simazine was less effective when applied 

at 0.8 kg ha –1 and 1.7 kg ha –1 and resulted in only 37 and 

71% reduction of T. officinale, respectively. A US study 

investigated the efficacy of buthidazole, metribuzin, 

simazine and 2,4-DB at various rates for the control of T. 

officinale (Sheaffer and Wyse 1982). Most herbicides temporarily 

reduced T. officinale populations, but only buthidazole 

continued to reduce populations in the year following 

application. However, control of T. officinale did not consistently 

increase alfalfa yield, and so the use of herbicides 

to control T. officinale in alfalfa cannot be recommended 

(Sheaffer and Wyse 1982). 

In other Canadian studies, T. officinale plants were tolerant 

to ethalfluralin applied at 1.1 kg a.i. ha –1 and incorporated 

into the soil prior to planting T. officinale as a crop for 

salad use in Québec (Michaud et al. 1993). Paraquat did not 

control T. officinale during fallow in the southern Canadian 


prairies because it has only contact action and will not affect 

the root (Blackshaw and Lindwall 1995). 

Maleic hydrazide has been used to control T. officinale in 

apple orchards in the USA. Plant numbers were reduced 

from 5.1–10.1 individuals m –2 in control plots to 2.6 individuals 

m –2 when maleic hydrazide was applied at a rate of 

6.7 kg ha –1 . Similar results were found for both spring and 

fall applications of the herbicide (Miller and Eldridge 1989). 

Mowing just before treatment with maleic hydrazide may 

have decreased T. officinale control (Miller and Eldridge 

1989). In another US study, Taraxacum officinale was controlled 

by quinclorac at 0.84 kg ha –1 and by a combination 

of clopyralid plus triclopyr at 0.16 kg ha –1 plus 0.47 kg ha –1 

respectively (Neal 1990). 

In a study in Virginia, USA, Chandran et al. (1998) found 

that a spring application of isoxaben at a rate of 0.56 kg ha –1 

in turfgrass caused 100% control of T. officinale 1 mo after 

application, where control was measured as emergence 

compared to untreated plots. However, control of T. officinale 

dropped to 62%, 1 yr after application. A fall application 

of isoxaben at 0.56 kg ha –1 resulted in 83% control of 

T. officinale after 1 yr. Results were similar for isoxaben 

applied at 0.84 kg ha –1 or 1.12 kg ha –1 . Control of T. officinale 

in plots that received both spring and fall applications 

of isoxaben was similar to control of T. officinale in plots 

receiving only fall applications. A spring application of oxadiazon 

at 3.36 kg ha –1 resulted in 100% control of T. officinale 

1 mo later, but after 1 yr, T. officinale abundance was 

greater in these treated plots than in untreated plots. The 

findings for fall applications of oxadizaon at this rate were 

similar, revealing that oxadiazon only provides short-term 

control of T. officinale (Chandran et al. 1998). 

Other chemicals have also been tested for their herbicidal 

efficacy on T. officinale. In laboratory experiments in the 

USA, allelopathic saponins from the roots of alfalfa had little 

effect on the germination of seeds or the growth of 

seedlings of T. officinale (Waller et al. 1993). The herbicidal 

efficacy of corn gluten meal, a waste product from corn 

milling, has been tested on T. officinale and other weeds 

(Quarles 1999). When applied at 324 g m –2 in greenhouse 

pot tests, corn gluten meal reduced survival of T. officinale 

by more than 75% by inhibiting root formation during germination. 

Under field conditions, corn gluten meal reduced 

the T. officinale population by about 90%, which was probably 

due to the combination of root inhibition and competition 

from Kentucky bluegrass (Quarles 1999). 

12. Response to Other Human Manipulations 

Integrated pest management strategies for T. officinale in 

turf include the selection of competitive turfgrass species, 

application of increased quantities of fertilizers, and 

mechanical control by mowing or removal. For example, 

studies in Ontario showed that Kentucky bluegrass was the 

least competitive of six turf species, perennial ryegrass was 

the most competitive and increased amounts of nitrogen fertilizer 

suppressed T. officinale in all turfgrass swards (Hall 

et al. 1992; Tripp 1997). Grass competition under frequent 

close mowing did not prevent T. officinale from surviving 

and spreading (Timmons 1950). Of four grasses tested,


native buffalograss was the most competitive with T. officinale 

(Timmons 1950). The size and average density of T. 

officinale plants can be reduced by decreasing the row spacing 

of grass crops (Darwent and Elliott 1979). 

Encroachment of T. officinale into turfgrass was greater 

in turf receiving limestone applications and tended to 

decrease with increasing phosphorus rates (Turner et al. 

1979). However, encroachment appeared to be more related 

to competition than the nutritional requirements of weeds 

since encroachment tended to decrease as the yield of turfgrass 

clippings increased (Turner et al. 1979). Phosphorus 

levels had a greater impact on growth of T. officinale than 

pH, with an application of 84 kg superphosphate ha –1 

increasing the yield of T. officinale tenfold compared to no 

added superphosphate, while added nitrogen had no effect 

(Zaprzalka and Peters 1982). Root growth was more responsive 

to differences in phosphorus and pH than top growth 

(Zaprzalka and Peters 1982). Tilman et al. (1999) showed 

that interspecific competition can be modified by changes in 

resource supply rates. For example, T. officinale had a higher 

requirement for potassium and its biomass was more limited 

by potassium than any of five common grass species 

tested, suggesting that it is a poorer competitor for potassium 

than these grasses. Also, T. officinale density and abundance 

were positively correlated with potassium levels in its 

tissues (Tilman et al. 1999). 

Taraxacum officinale control was greater in plots 

of Kentucky bluegrass treated with 600 kg N ha –1 than 

when treated with 300 kg N ha –1 , even though both levels 

are very high (Johnson and Bowyer 1982). This supported 

the findings of Zahnley and Duley (1934) who found that 

after they had fertilized and produced a dense growth of 

grass, T. officinale seedlings did not become established 

readily and growth was repressed by competition from the 

grass. Competition was further increased by cutting the 

grass at a greater height, which tended to shade the ground 

and retard the development of T. officinale (Zahnley and 

Duley 1934). 

Mechanical removal of T. officinale plants has been of 

limited value, as the long taproot must be entirely removed. 

Even small pieces of root can propagate new plants 

(Warmke and Warmke 1950; Mann and Cavers 1979). In 

addition, debudding or defoliation of the plant can result in 

a shift of the shoot-root ratio, favouring root growth and 

exacerbating the problem (Letchamo and Gosselin 1995). 

Struik (1967) studied the reaction of T. officinale to different 

grassland management regimes; mown, heavily grazed, 

lightly grazed, and uncut. As the degree of defoliation 

increased, plant radius decreased, length of the longest leaf 

decreased, root length decreased, leaf number increased and 

plant form changed from upright to slanting and appressed. 

Percent cover with T. officinale was significantly higher in 

a long-term grazed treatment (Popolizio et al. 1994). 

Taraxacum officinale is able to rapidly replace a large quantity 

of leaves relative to other organs during short periods 

(every 30–50 d) between mowing (Sawada et al. 1982), 

partly due to increased light availability (von Hofsten 1954). 

Cutting the scapes of T. officinale in bud or in flower resulted 

in the production of seeds that were non-viable, while 

cutting the scapes after the seeds had ripened resulted in 

91% seed germination (Gill 1938). 

Significantly higher chlorophyll content, and root and 

shoot growth were found under hydroponic culture of T. 

officinale (Letchamo and Gosselin 1995). Debudding the 

plants under hydroponic medium increased root yield by 

131% compared with the control (Letchamo and Gosselin 

1995). 

Occurrence of T. officinale is greater in crop rotation systems 

with a high frequency of broadleaf crops (four rotations 

with broadleaf crops in 3 of 4 yr) compared to a low 

broadleaf frequency of broadleaf crops (three rotations with 

broadleaf crops in 2 of 4 yr) (Stevenson and Johnston 1999). 

On the semi-arid Canadian prairies, T. officinale was present 

in all crop rotations examined; continuous winter wheat, 

winter wheat-fallow, winter wheat-spring canola, winter 

wheat-lentil or flax (Blackshaw et al. 1994). Densities were 

higher in minimum and zero-till treatments than in conventional 

till (Légère et al. 1993; Blackshaw et al. 1994). 

Tillage frequency has been shown to have an impact on 

germination and establishment of T. officinale. In spring 

wheat in clay soil in northern Alberta, higher densities of T. 

officinale were found under zero tillage systems than under 

other systems (Arshad et al. 1994). In eastern Canada, density 

was higher in alfalfa that had been seeded directly into 

grain stubble, as compared to conventionally-seeded alfalfa 

(Rioux 1994). In sweet corn, T. officinale emergence was 

not affected by tillage, probably because of the short time 

between seed dispersal and germination (Mohler and 

Calloway 1992). The presence of crown vetch as a living 

mulch reduced T. officinale numbers by 74% in no-tillage 

corn (Hartwig 1989). In the UK, the occurrence of T. officinale 

in plots sown with spring barley was inversely proportional 

to cultivation frequency. Plots that were never 

cultivated had a total of 196 T. officinale plants m –2 . Yearly 

cultivation resulted in 72 plants m –2 , quarterly cultivation 

resulted in 54 plants m –2 , and monthly cultivation resulted 

in 33 plants m –2 (Chancellor 1964). 

Taraxacum officinale can survive after tillage with a 

plough or disc, because of its ability to regenerate from root 

sections (von Hofsten 1954). However, Falkowski et al. 

(1990) reported ploughing to be an effective method of 

eliminating T. officinale because the lower parts of roots 

were less viable than the upper parts, which were buried by 

ploughing. Flame weeding in pear and apple orchards 

favours the growth of T. officinale (Ferrero et al. 1994). 

The timing and frequency of harvesting also influences 

the degree of dandelion infestation. Moyer et al. (1999) 

found that the growth-stage-based harvest times of alfalfa 

affected encroachment by T. officinale and the resultant 

alfalfa quality. For example, when alfalfa was harvested at 

the vegetative or prebud stage, it contained 25% T. officinale 

by weight, but when it was harvested at any other stage 

such as flowering, it contained

ther radiation, and a change in the rate of growth and development 

(Pozolotina 1996). The potential use of electromagnetic 

radiation in the form of microwaves has been studied 

for T. officinale control on railway tracks in Europe 

(Kunisch et al. 1992). Plants were killed by microwave 

treatment for 16 s, which increased the soil temperature by 

more than 40°C in controlled environments (Kunisch et al. 

1992). 

13. Response to Herbivory, Disease and Higher 

Plant Parasites 

Herbivory 

(a) Mammals, including both domestic and wild animals. 

Mammals, including rabbits, cats, chipmunks, ground squirrels, 

groundhogs (woodchucks), prairie dogs, pocket 

gophers, deer, moose, elk, black bears and grizzly bears, eat 

the leaves of T. officinale (Ellison and Aldous 1952; Powell 

1972; Angier 1980; Jackson 1982; Swihart 1990). 

Dandelion is an excellent pasture feed for dairy cattle, 

improving milk flow and quality (Jackson 1982). However, 

manure from cattle can contain viable seeds and, when 

applied to cropland, may serve as a source of introduction 

and dispersal (Mt. Pleasant and Schlather 1994). Domestic 

animals, such as goats and pigs, eat the seeds (Powell 1972), 

and sheep and geese have been used for biological control of 

T. officinale, with sheep being more effective than geese in 

controlling the weed in Christmas tree plantations in North 

Carolina, USA. (Müller et al. 1999). 

(b) Birds and/or other vertebrates. Taraxacum officinale 

seeds are eaten by at least 12 songbirds native to Canada 

(Jackson 1982). Birds such as siskins, common house finches, 

goldfinches and sparrows eat the seeds (Longyear 1918; 

Angier 1980). Leaves, inflorescences and seed heads are 

eaten by chickens, ducks, geese, Canada geese, grouse, partridges, 

pheasants, prairie chickens, quail, ruffed grouse and 

sage grouse (Eckert et al. 1973; Angier 1980; Jackson 

1982). Seed predation by birds, ants and rodents reduced 

seed number and seedling emergence of T. officinale more 

where ground cover was dense (in hollows) than in less 

dense communities (on ridges) (Reader and Beisner 1991). 

Thus, ground cover can restrict seedling emergence by providing 

a habitat for seed predators (Reader 1991b). 

(c) Insects and Arachnids. Due to its early flowering and 

rich supply of nectar, T. officinale is a food source for many 

insects, including butterflies, bee flies, hawk moths and 

bumblebees in Canada (Jackson 1982). Judd (1971) collected 

152 species of insects in the Orders Collembola, 

Thysanoptera, Hemiptera, Homoptera, Coleoptera, Diptera 

and Hymenoptera from the inflorescences of T. officinale in 

Ontario. 

The cynipid wasp, Phanacis taraxaci (Ashmead), forms 

galls on the abaxial surfaces of maturing T. officinale leaves 

in Canada and the USA. These galls influence the partitioning 

of photoassimilates by actively redirecting carbon 

resources from unattacked leaves (Paquette et al. 1993; 

Bagatto et al. 1996). The first record of European dandelion 

leaf-gall midge, Cystiphora taraxaci Kieffer, in north-cen- 


tral Saskatchewan was by Peschken et al. (1993). This 

midge induces purple-red pustule galls on the upper surfaces 

of leaves (Neuer-Markmann and Beiderbeck 1990). T. officinale 

is also a host for the braconid Pholetesor ornigis 

(Weed), a parasitoid that attacks larvae of the leaf miner 

Phyllonorycter blancardella (Fabr.), which is a pest of apple 

in Canada (Hagley and Barber 1992). 

Taraxacum officinale also acts as a host for several aphid 

species. In Canada, Aphis knowltoni Hottes & Frison has 

been collected from roots of T. officinale (Wood-Baker 

1980), and Aphis taraxacicola (Börner) has been recorded 

on T. officinale in Japan (Sugimoto and Takahashi 1996). In 

the USA, T. officinale is a favourite secondary weed host of 

the green peach aphid (Myzus persicae Sulzer) during the 

summer (Kaakeh and Hogmire 1991). In the UK, it is a natural 

host of the lettuce root aphid, Pemphigus bursarius (L.) 

(Gange and Brown 1991). 

In the USA, the weevil, Ceutorhynchus punctiger 

Gyllenhall, attacks T. officinale inflorescence buds, seeds 

and leaves (McAvoy et al. 1983). McAvoy et al. (1983) suggested 

that C. punctiger could be used as a biocontrol to 

reduce the viable seed population of T. officinale but host 

specificity and key mortality factors of the weevil must first 

be studied. Another weevil, Barypeithes pellucidus 

(Boheman), feeds lightly on T. officinale leaves but moderately 

on the epidermis of the scapes (Galford 1987). In laboratory 

experiments, the boll weevil, Anthonomus grandis 

Boheman, a pest of cotton, feeds and survives on T. officinale 

cuttings for 8–10 d by eating pollen and seed heads. 

Therefore, feral boll weevils, emerging prior to cotton flowering, 

may initially survive on T. officinale plants and subsequently 

infest cotton crops in the USA (Haynes and Smith 

1992). The black vine weevil, Otiorhynchus sulcatus (Fab.), 

also feeds on T. officinale in Japan and the UK; although 

some resistance is conferred by mycorrhizal associations 

(Masaki et al. 1984; Gange et al. 1994). 

Taraxacum officinale is a host for many other insects in 

the USA. These include several caterpillars, such as those of 

the cabbage looper (Trichoplusia ni Hübner), the yellowstriped 

armyworm (Spodoptera ornithogalli) (Dussourd and 

Denno 1994), and the tiger moth (Diacrisia virginica Fabr.), 

which prefers to feed on T. officinale over grasses (Dethier 

1993). It is also a host for the small milkweed bug, Lygaeus 

kalmii Stal. (Fox and Caldwell 1994), but significantly 

fewer of these bugs survived on T. officinale than on milkweed 

species. Nymphs of the potato leafhopper, Empoasca 

fabae (Harris), develop and adults survive and reproduce on 

T. officinale (Lamp et al. 1984). It was suggested that the 

leafhopper may have a role as a biological weed control 

agent. Crickets [Allonemobius allardi (Alexander & 

Thomas)] have also been recorded feeding on leaves of T. 

officinale (Jacobs et al. 1992). Root feeding larvae of the 

Japanese beetle (Popillia japonica Newman) and the southern 

masked chafer (Cyclocephala lurida Bland), commonly 

called white grubs, feed upon and reduce root biomass of T. 

officinale (Crutchfield and Potter 1995). 

In Japan, the coccinellid Coccinula crotchi (Lewis) survives 

on inflorescences of various species, including T. 

officinale (Hoshikawa 1995). Also, adult scarab beetles,


Anomala octiescostata Burmeister, are attracted to and 

voraciously feed on its inflorescences (Leal et al. 1994). 

This attraction is mediated by the chemical kairomone (Leal 

et al. 1994). 

In Germany and Switzerland, T. officinale is the most 

important food plant for larvae of cockchafers, also called 

May or June beetles (Melolontha melolontha L.) and, for 

egg-laying, the females preferred soil under T. officinale 

more than soil under other dicotyledons and grasses 

(Schütte and Hauss 1985; Keller 1986; Schütte 1996). Von 

Hofsten (1954) reported the following insects on T. officinale 

in Sweden: Paroxyna tessellata Loew., Dolycoris baccarum 

L., Corizus hyoscyami L., Stictopleurus crassicornis 

L., Carpocoris pudicus Poda., Polomena pracina L. and 

Hepiolus humili L.. Kuusi et al. (1984) recorded turnip root 

fly (Delia floralis Wied.), cabbage moth (Mamestra brassicae 

L.) and pollen beetle (Meligethes aeneus F.) on T. officinale 

in Finland. 

The mite, Epitrimerus taraxaci Liro, inhabits the leaves of 

T. officinale causing discolouration and russeting in 

Yugoslavia (Petanovic 1990). This mite has a narrow host 

range but it includes several cultivated plants as well as weeds. 

(d) Nematodes and/or other non-vertebrates. In the USA, T. 

officinale acts as a host to two dagger nematodes, 

Xiphinema americanum Cobb and X. rivesi Dalmasoo, 

which can transmit plant viruses (Georgi 1988a,b). 

Members of the Meloidogyne sp. Goeldi have also been 

found on T. officinale in Canada and the USA, as well as 

Meloidogyne incognita (Kofoid & White) Chitwood, 

Ditylenchus destructor Thorne and Pratylenchus penetrans 

(Cobb) Chitwood & Oteifa in the USA (Anonymous 1960; 

Conners 1967). 

Other non-vertebrates such as slugs, snails and earthworms, 

also use T. officinale as a host. In UK studies, slugs 

of the genus Deroceras found T. officinale highly palatable 

in a number of feeding trials (Duval 1971; Dirzo 1980; 

Cook et al. 1996; Hanley et al. 1996) and younger seedlings 

were grazed more severely by the reticulated slug 

Deroceras reticulatum (Müller) (Hanley et al. 1995). D. 

reticulatum and another slug, Arion lusitanicus (Mabille), 

damage oilseed rape and other arable crops in Europe. In 

food choice trials, T. officinale was very attractive to A. lusitanicus 

and rape was not significantly more defoliated than 

T. officinale (Frank and Friedli 1999). The authors even recommended 

sowing T. officinale (and other weeds) in high 

quantities into fields of rape to prevent severe slug damage. 

In other European studies, the land snail (Helix aspersa 

Müller) and juvenile earthworms (Lumbricus terrestis L.) 

also found T. officinale highly palatable (Daniel 1991; 

Desbuquois and Daguzan 1995). 

Diseases. Microorganisms reported from T. officinale worldwide 

are listed in Table 1 and those recorded in Canada have 

been reviewed by Conners (1967) and Ginns (1986). 

(a) Fungi. Numerous fungi have been reported on T. officinale 

in Canada and some of the more important examples 

are discussed here. Puccinia taraxaci Plowr., a rust fungus, 

forms numerous, minute, dark brown pustules on leaves 

(Longyear 1918; Conners 1967). Another fungus 

Synchytrium taraxaci de Bary & Woronin, causes tiny 

swellings or galls on leaves that can lead to partial stunting 

(Longyear 1918; Ginns 1986). The powdery mildew fungi 

Sphaerotheca fuliginea (Schlect. Ex Fr.) Poll., S. humili var. 

fuliginea (Schlect.) Salm. and S. macularis (Wallr.:Fr.) have 

been recorded (Conners 1967; Ginns 1986). In cultivated T. 

officinale in Germany and Finland, powdery mildew 

reduces yields and requires control with fungicides (Kuusi 

et al. 1984; von Hinrichs 1988). but Longyear (1918) 

observed only slight damage in the USA. 

Phoma exigua (Desm.) and P. herbarum (Westend.) have 

been isolated from T. officinale in Ontario and considered as 

potential biocontrol agents (Neumann Brebaum 1998; 

Neumann Brebaum and Boland 1999). P. taraxaci Hofsten 

was considered as a biocontrol agent for T. officinale in 

Sweden (von Hofsten 1954). P. taraxaci spread by pycnospores 

and infected seeds, however, it was extremely 

variable with respect to its pathogenicity on T. officinale and 

its viability in soil. Von Hofsten (1954) also mentioned an 

unnamed “ring-forming fungus” which released a substance 

that was highly toxic to T. officinale and other plants. 

Sclerotinia species have also been tested as biological 

control agents for T. officinale in Canada (Riddle et al. 

1991). Sclerotinia sclerotiorum (Lib.) de Bary and S. minor 

Jagger were evaluated in a controlled environment and in 

turfgrass swards for their virulence on T. officinale. Isolates 

of both species reduced the dry weight of plants in a controlled 

environment and reduced the number of plants in turfgrass 

swards. Heat-killed seeds of perennial ryegrass were 

suitable as both a growth substrate for Sclerotinia spp. and 

a delivery system to T. officinale (Riddle et al. 1991). 

Sclerotinia sclerotiorum caused localized infection on the 

leaf laminas of T. officinale when artificially inoculated as a 

mycelium-on-wheat preparation (Waipara et al. 1993). 

Also, S. sclerotiorum created basal necroses of 1–2 cm in 

length on tap roots. These necroses inhibited leaf regrowth 

from the root after defoliation (Burpee 1992). Sclerotinia 

minor, produced in a granular sodium alginate formulation 

or on autoclaved barley grains, is also considered a potentially 

effective biological control agent against T. officinale 

(Ciotola et al. 1991; Brière et al. 1992). 

(b) Bacteria. The bacterium, Pseudomonas syringae pv. 

tagetis Hellmers, has been isolated from T. officinale in the 

USA where it caused apical chlorosis and necrotic leaf spots 

(Rhodehamel and Durbin 1985). Sterk et al. (1987) reported 

that Agrobacterium tumefaciens (Smith and Townsend) 

Conn is found on Taraxacum species in the Netherlands, 

causing galls on the roots and, sometimes, the leaves. 

(c) Viruses. More than twenty viruses can infect T. officinale, 

with some causing severe mottling and leaf malformation 

symptoms. Dandelion yellow mosaic virus (DYMV) 

causes a yellow mottle (chlorotic rings and spots) on T. 

officinale and also infects lettuce (Kassanis 1947; Bos et al. 

1983). The virus can be transmitted by aphids (Kassanis 

1947; Bos et al. 1983) and is similar to parsnip yellow fleck

Table 1. Microorganisms reported from T. officinale worldwide 


Organism Reference Geographical region 

Agrobacterium tumefaciens (Smith and Townsend) Conn Sterk et al. (1987) Netherlands 

Alfalfa mosaic virus Brcák (1979) Czechoslovakia, Scandinavia 

Arabis mosaic virus (Arabis mosaic nepovirus) Brcák (1979), Brunt et al. (1996) Czechoslovakia, Scandinavia 

Argentine plantago virus Gracia et al. (1983) Argentina 

Aster Yellows (phytoplasma) Wang and Hiruki (2001) Canada 

Ascochyta doronici Allesch. Farr et al. (1989) USA 

Beet pseudo yellows virus Duffus (1965), Duffus and Johnstone Australia, Spain 

(Beet pseudo–yellows closterovirus) (1981), Soria et al. (1991), Brunt et al. (1996) USA 

Botrytis cinerea Pers. ex Fr. Anonymous (1960), Kuusi et al. (1984), Farr et al. (1989) Finland, USA 

Canola Yellows (phytoplasma) Wang and Hiruki (2001) Canada 

Centrospora acerina (R. Hartig) A. G. Newhall Tompkins and Hansen (1950) USA 

Ceratobasidium anceps (Bres.&Syd.) Conners (1967) Canada 

Cherry rasp leaf virus (Cherry rasp leaf nepovirus) Brcák (1979), Brunt et al. (1996) Czechoslovakia, Scandinavia 

Chrysanthemum latent virus` Brcák (1979) Czechoslovakia, Scandinavia 

Colletotrichum dematium (Fr.) Grove Conners (1967) Canada 

Colorado red-node virus Thomas (1949) USA 

Cucumber mosaic virus Brcák (1979) Czechoslovakia, Scandinavia 

Dandelion carlavirus Dijkstra et al. (1985), Brunt et al. (1996) Netherlands 

Dandelion latent carlavirus Johns (1982), Brunt et al. (1996) Canada 

Dandelion necrotic blotch Brcák (1979) Czechoslovakia, Scandinavia 

Dandelion necrotic ringspot virus (Dandelion mosaic virus) Cech and Branisová (1973) Czechoslovakia 

Dandelion yellow mosaic virus (Dandelion yellow Moore (1946), Kassanis (1947), Brcák (1979), Czechoslovakia, Netherlands, 

mosiac sequivirus, Yellow mosaic lettuce virus, 

Lettuce necrosis virus) 

Bos et al. (1983), Brunt et al. (1996) Scandinavia, UK 

Ditylenchus dipsaci (Kuehn) Filip. Anonymous (1960) USA 

Erisiphe cichoracearum DC. Ubrizsy (1946), Anonymous (1960), Farr et al. (1989), 

von Hinrichs (1989) 

Germany, Hungary, USA 

European yellows virus Blattny et al. (1954) Czechoslovakia 

Grapevine yellows (MLO) Arzone et al. (1995) Italy 

Italian clover phyllody Firrao et al. (1996) Italy 

Kok-Sagyyz virus Ryjkoff (1943) USSR 

Lettuce big-vein virus Campbell (1969), Brcák (1979), Demírcí et al. (1995) Czechoslovakia, Scandinavia, 

Turkey, USA 

Lettuce mosaic virus Brcák (1979) Czechoslovakia, Scandinavia 

Lettuce virus Anonymous (1948) Switzerland 

Longidorus euonymus (Nematoda: Dorylaimida) Romanenko and Korchinsky (1994) Russia 

Olpidium brassicae (Woronin) P. A. Dang Ginns (1986) Canada 

Peach rosette moasic virus (Peach rosette mosaic nepovirus) Ramsdell and Myers (1978), Brunt et al. (1996) USA 

Petunia asteroid mosaic virus Fuchs et al. (1994) Germany 

Phoma exigua (Desm.) Neumann Brebaum and Boland (1999) Canada 

Phoma herbarum (Westend.) Neumann Brebaum and Boland (1999) Canada 

Phoma taraxaci Hofsten von Hofsten (1954) Sweden 

Phyllactinia corylea Pers. ex Karst. Anonymous (1960) USA 

Phyllactinia guttata (Wallr.:Fr.) Lév Shaw (1973), Farr et al. (1989) USA (Pacific Northwest) 

Phynatotrichopsis omnivora (Duggar) Hennebert Anonymous (1960), Farr et al. (1989) USA 

Physarum cinereum (Batsch) P. Farr et al. (1989) USA 

Plasmopara halstedii (Farl.) Berl. & De Toni in Sacc. Anonymous (1957) Canada (Québec) 

Potato y virus Lytaeva (1971), Brcák (1979) Czechoslovakia, Scandinavia, 

USSR 

Potato parastolbur virus Valenta et al. (1961) Slovakia 

Protomyces pachydermus Thümen Seymour (1929), Anonymous (1960), 

Farr et al. (1989), Ellis and Ellis (1997) 

USA 

Pseudomonas syringae pv. tagetis Hellmers Rhodehamel and Durbin (1985) USA 

Pseudomonas tabaci (Wolf & Foster) Stapp Anonymous (1960) USA 

Pseudomonas viridiflava (Burkholder) Dowson Gitaitis et al. (1998) USA 

Puccinia hieracii (Röhling) Mart. Seymour (1929), Anonymous (1960), Conners (1967), 

Shaw (1973), Alfieri et al. (1984), Ellis and Ellis (1997) 

Ginns (1986), Farr et al. (1989) 

Canada, USA (Pacific Northwest) 

Puccinia taraxaci Plowr. Anonymous (1960), Conners (1967), 

Stojanovic et al. (1993) 

Canada, USA, Yugoslavia 

Puccinia variabilis Grev. Seymour (1929), Anonymous (1960), Conners, (1967), 

Alfieri et al. (1984), Ellis and Ellis (1997), 

Farr et al. (1989) 

Canada, USA 

Ramularia lineola Pk. Anonymous (1960), Farr et al. (1989) USA 

Ramularia taraxaci Karsten Seymour (1929), Anonymous (1960), Conners (1967), 

Shaw (1973), Kuusi et al. (1984), Ellis and Ellis (1997), 


Canada, USA (Pacific Northwest)


Table 1. Continued 

Rhizoctonia solani Kühn Chesters and Assawah (1956), Anonymous (1960), Canada, USA 

Conners (1967), Farr et al. (1989) 

Sclerotinia minor Jagger Ciotola et al. (1991), Riddle et al. (1991), North America 

Brière et al. (1992) 

Sclerotinia sclerotiorum (Lib.) de Bary Anonymous (1960), Shaw (1973), Alfieri et al. (1984), North America 

Farr et al. (1989), Riddle et al. (1991) 

Sclerotinia trifoliorum Eriks. Pape (1954) Germany 

Sclerotium rolfsii Sacc. Alfieri et al. (1984), Farr et al. (1989) USA 

Septoria britannica Trott Farr et al. (1989) USA 

Septoria unicolor Wint. Anonymous (1960), Shaw (1973), Farr et al. (1989) USA 

Sphaerotheca erigerontis–canadensis (Lév.) L. Junnell Seymour (1929), Ellis and Ellis (1997) North America 

Sphaerotheca fuliginea (Schlecht. ex Fr.) Poll. Anonymous (1960), Conners (1967), Kuusi et al. (1984), Canada, USA 


Sphaerotheca humili var. fuliginea (Schlecht.) Salm Anonymous (1960), Conners (1967), Ginns (1986) Canada, USA 

Sphaerotheca macularis (Wallr. ex Fr.) Conners (1967), Shaw (1973), Ginns (1986), Canada, USA 

Farr et al. (1989) 

Stolbur phytoplasma ˇ Skoric et al. (1998), Viczián et al. (1998) Croatia, Hungary 

Strawberry green petal virus Misiga et al. (1960) Czechoslovakia 

Strawberry latent ringspot nepovirus Brunt et al. (1996) Germany 

Synchytrium sp. de Bary & Woronin Longyear (1918) USA 

Synchytrium taraxaci de Bary & Woronin Seymour (1929), Anonymous (1960), Shaw (1973), Canada, Germany, USA 

Ginns (1986), Farr et al. (1989), Triebel and 

Rambold (1990), Ellis and Ellis (1997) 

Tobacco rattle virus Brcák (1979) Czechoslovakia, Scandinavia 

Tobacco ringspot virus Tuite (1960), Brcák (1979) Czechoslovakia, Scandinavia, 

USA 

Tomato black ring virus Brcák (1979) Czechoslovakia, Scandinavia 

Tomato ringspot virus Brcák (1979), Mountain et al. (1983), Barrat et al. (1984) Czechoslovakia, Scandinavia 

Powell et al. (1984), Powell et al. (1992), USA 

Ramsdell et al (1993) 

Vermicularia dematium (P) ex Fr, var. minor Sacc. Farr et al. (1989) USA 

Verticillium albo-atrum Rfe. et Beth. Müller (1969) Germany 

Xylella fastidosa Leite et al. (1997) Brazil 

Yellows (MLO) Dale (1972) USA 

Yellows-virus (Chlorogenus callistephi Holmes, Anonymous (1960) USA 

Calistephus virus 1 K.M.Sm) 

virus (PYFV) (Murant 1988). Tomato ringspot virus 

(TmRSV) reduces the top weight and inflorescence production 

of T. officinale under field conditions (Powell et al. 

1992). TmRSV affects plants that are mowed regularly more 

adversely than those not mowed (Powell et al. 1992). 

Infected plants may serve as donor plants for TmRSV transmission 

by Xiphinema rivesi, a dagger nematode, and can 

transmit TmRSV to progeny via seeds (Mountain et al. 

1983). The density of Taraxacum officinale had a weak positive 

correlation with percentage of TmRSV-infected prune 

trees in a commercial orchard (Ramsdell et al. 1993). 

In the Okanagan Valley, BC, a carlavirus with the proposed 

name of dandelion latent virus (DLV), was isolated 

from naturally infected T. officinale exhibiting no visible 

symptoms (Johns 1982). Another carlavirus was isolated 

from T. officinale plants that displayed slight mottling and 

leaf malformation (Dijkstra et al. 1985). This latter virus 

was not seed transmitted and the name dandelion carlavirus 

has been proposed. In Argentina, a potexvirus caused severe 

mosaic and leaf malformations on T. officinale plants and 

was provisionally named Argentine plantago virus (AplaV) 

(Gracia et al. 1983). Taraxacum officinale is also a host for 

a yellowing disease caused by beet pseudo yellows virus 

(BPYV) (Duffus 1965; Soria et al. 1991). Older leaves of 

infected plants display reddening and chlorosis of interveinal 

areas and the agent is transmitted by greenhouse 

whitefly (Trialeurodes vaporariorum Westwood). None of 

the viruses described (Table 1) has been considered as a biological 

control agent for T. officinale. 

In Alberta, plants of T. officinale displaying yellows symptoms 

were examined using molecular techniques and two different 

phytoplasmas were detected (Wang and Hiruki 2001). 

One was identified as a member of the canola yellows subgroup 

16SrI-A, while the other was classified as a member of 

a distinct subgroup in the aster yellows group (Wang and 

Hiruki 2001). Plants of T. officinale exhibiting typical symptoms 

of mycoplasma-like organism (MLO) infection were 

reported in Italy (Terlizzi et al. 1994) and MLO-like bodies 

were observed using electron microscopy. In a separate 

study, Firrao et al. (1996) characterized an MLO from T. 

officinale called Italian Clover Phyllody (ICPh) phytoplasma, 

which caused yellowing/reddening, virescence and phyllody. 

ACKNOWLEDGEMENTS 

The authors would like to thank Aaron Goldwater and 

Melody Melzer (The University of Guelph), for technical 

assistance. The authors also thank herbaria staff from across 

Canada for information and specimen loans, William Cody 

(DAO Herbarium, Ottawa) for assistance with distribution 

records, and Rob Bowman and Rob Guthrie (The University 

of Guelph) for assistance with compiling the distribution 

map. The assistance and advice of Jacques Cayouette 

(AAFC, Ottawa) and the two anonymous reviewers is gratefully 

acknowledged.

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