Linaria Mill.
As traditionally circumscribed Linaria is a genus with about 150 species in Eurasia and the Mediterranean area (Sutton 1988, Mabberley 2008). The genus is particularly well-represented in Europe with 70 or more species (e.g. Chater & al. 1972). Many species occur outside their native distribution range and residence status for some of the Belgian representatives is uncertain. L. vulgaris Mill. is a common and widespread native species (Lambinon & Verloove 2012). L. arvensis (L.) Desf. probably also is a native. It was thought to be extinct since 1909 (van Rompaey & Delvosalle 1978) but it was recently rediscovered on the gravelly banks of river Maas (Van Braeckel & Van Looy 2005). L. repens (L.) Mill. is also accepted as native although at least part of its populations is more likely introduced (e.g. on coal mining spoil heaps, railway yards, etc.). It is known to persist rather rarely (van Rompaey & Delvosalle 1978) which also may point to a doubtful native status.
Recent molecular data have shown that Linaria is monophyletic after inclusion of the New World genus Nuttallanthus Sutton (Fernández-Mazuecos & al. 2013). In the same study it was shown that many of the previously recognized sections are not monophyletic.
Rather numerous species of Linaria are cultivated as ornamentals. Useful accounts are provided by De Wolf (1956), Gardner & Maxwell (2000) and Jäger & al. (2008). Others are weeds of agricultural fields, especially in cereals. Several of these, garden escapes as well as cereal weeds, have been recorded as aliens in Belgium.
For a reliable identification plants with both flowers and ripe seeds are often required. Several groups are particularly difficult in terms of taxonomy and identification. Especially the Linaria vulgaris and L. supina complex may hide as yet in Belgium unrecognized critical taxa. Further study is needed in these groups.
Several additional species are to be expected. Perhaps most likely is Linaria dalmatica (L.) Mill. (syn.: L. genistifolia (L.) Mill. subsp. dalmatica (L.) Maire & Petitm.). It is much reminiscent of native L. vulgaris but has wider leaves and slightly longer corollas (up to 55 mm long). Also, its seeds are angular, not discoid. It is known from most neighboring countries (e.g. Jäger & Werner 2005, Stace 2010, Denters 2013) and is often considered an invasive species (e.g. Vujnovic & Wein 1997, Sing & Peterson 2011).
1 Corolla mainly yellow === 2
Corolla mainly violet, blue, purple or white === 6
2 Annual. Seeds trigonous or quadrangular, not winged. Corolla 15-40 mm long === 3
Perennial or annual. Seeds discoid, broadly winged. Corolla 5-35 mm long === 4
3 Style undivided. Leaves oblong-lanceolate, semi-amplexicaul, 4-18 mm wide. Inflorescence dense. Calyx lobes conspicuously unequal === Linaria hirta
Style bifid. Leaves linear, sessile, less than 4 mm wide. Inflorescence lax. Calyx lobes more or less equal === L. bipartita Hybrids p.p.
4 Corolla 5-9 mm long. Always annual === L. simplex
Corolla 13-35 mm long. Annual, biennial or perennial === 5
5 Annual (usually). Stem procumbent to ascending, bare of leaves below inflorescence. Corolla 13-20 mm, pale yellow (sometimes tinged with violet). Calyx lobes unequal === L. supina
Perennial (always). Stem erect, more or less leafy up to inflorescence. Corolla 25-33 mm, pale or bright yellow (never tinged violet). Calyx lobes equal (native) === L. vulgaris
6 Corolla uniformly white, with curved spur === L. chalepensis
Corolla violet, blue or purple; if white, then with straight spur === 7
7 Spur longer than the rest of the corolla. Annual === L. bipartita Hybrids p.p.
Spur much shorter than to nearly as long as the rest of the corolla. Perennial or annual === 8
8 Annual. Corolla minute, 4-7 mm, with strongly curved spur (native) === L. arvensis
Perennial. Corolla 8-55 mm, spur straight or slightly curved === 9
9 Corolla 35-55 mm long. Seeds discoid, with a distinct wing === L. triornithophora
Corolla 8-15 mm long. Seeds trigonous to angular, without wing === 10
10 Corolla purple-violet (white in cultivars). Spur curved, more than half as long as the rest of the corolla. Inflorescence elongate and very dense, even in fruit === L. purpurea
Corolla white to pale lilac, with violet veins. Spur straight, less than half as long as the rest of the corolla. Inflorescence not elongate and rather lax, especially in fruit (native) === L. repens
Additional aliens: Linaria angustissima (Loisel.) Borbás (Eur., vector unknown) and L. genistifolia (L.) Mill. (Euras., grain alien?). Linaria latifolia Desf., an endemic from the western Mediterranean, was recorded as a weed in containers with imported olive trees in 2009 (see below).
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Literature:
Chater A.O., Valdés B. & Webb D.A. (1972) Linaria. In: Tutin T.G. & al. (eds.), Flora Europaea, volume 2. Cambridge University Press, Cambridge: 226-236.
De Wolf G.P. (1956) Notes on cultivated Scrophulariaceae. 3. Linaria. Baileya 4: 102-114.
Denters T. (2013) Bijzondere plantenvondsten in de regio Amsterdam 2010-2012. Available online at: http://www.frontlinie.nl/floron/vondsten%202010_2012(3).pdf.
Fernández-Mazuecos M., Blanco-Pastor J.L. & Vargas P. (2013) A Phylogeny of Toadflaxes (Linaria Mill.) Based on Nuclear Internal Transcribed Spacer Sequences: Systematic and Evolutionary Consequences. International Journal of Plant Sciences 174(2): 234-249.
Gardner M.F. & Maxwell H.S. (2000) Linaria. In: Cullen J. & al. (eds.), The European Garden Flora, vol. 6. Cambridge University Press, Cambridge: 311-313.
Jäger E.J., Ebel F., Hanelt P. & Müller G. (eds.) (2008) Rothmaler Band 5. Exkursionsflora von Deutschland. Krautige Zier- und Nutzpflanzen. Springer Verlag, Berlin: 880 p.
Jäger E.J. & Werner K. (eds.) (2005) Rothmaler Band 4. Exkursionsflora von Deutschland. Gefässpflanzen: Kritischer Band. Springer Verlag, Berlin: 880 p.
Lambinon J. & Verloove F. (avec coll. Delvosalle L., Toussaint B., Geerinck D., Hoste I., Van Rossum F., Cornier B., Schumacker R., Vanderpoorten A. & Vannerom H.) (2012) Nouvelle Flore de la Belgique, du Grand-Duché de Luxembourg, du Nord de la France et des Régions voisines (Ptéridophytes et Spermatophytes). Sixième édition. Jardin botanique national de Belgique, Meise: CXXXIX + 1195 p.
Mabberley D.J. (2008) Mabberley’s plant-book (3th ed.). Cambridge University Press, Cambridge: XVIII + 1021 p.
Sáez L. & Bernal M. (2009) Linaria. In: Benedí C. & al. (eds.), Flora Iberica, vol. XIII. Plantaginaceae-Scrophulariaceae: 233-324. Real Jardín Botánico, Madrid. C.S.I.C. [available online at: http://www.floraiberica.es/floraiberica/texto/pdfs/13_144_11_Linaria.pdf]
Sáez L. Sainz M. & Crespo M.B. (2004) Taxonomic notes on Linaria Mill. (Scrophulariaceae) for Flora Iberica. Folia Geobot. 39: 293-318.
Sing S.E. & Peterson R.K. (2011) Assessing environmental risks for established invasive weeds: Dalmatian (Linaria dalmatica) and yellow (L. vulgaris) toadflax in North America. Int. J. Environ. Res. Public. Health. 8(7): 2828-2853. [available online at: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3155332/]
Stace C. (2010) New flora of the British Isles, 3th ed.: XXXII + 1232 p. Cambridge University Press.
Sutton D.A. (1988) A revision of the tribe Antirrhineae. Oxford University Press, Oxford.
Tison J.-M. & de Foucault B. (coord.) 2014) Flora Gallica. Flore de France. Editions Biotope, Mèze : xx + 1196 p.
Valdés B. (1970) Revisión de las especies europeas de Linaria con semillas aladas. Publicaciones de la Universidad de Sevilla.
Van Braeckel A. & Van Looy K. (2005) Gemeenschappelijke Maas: Ecologische effecten van ingreepscenario’s, centrale sector van Maasmechelen tot Maaseik. Verslag van het Instituut voor Natuurbehoud. 2005.06: 115 p. [available online at: https://www.inbo.be/sites/alienplantsbelgium.bedefault/files/bestanden/bijlagen/gemeenschappelijke-maas_in.pdf]
Van Rompaey E. & Delvosalle L. (1978) Atlas de la flore belge et luxembourgeoise. Ptéridophytes et Spermatophytes. Commentaires. Jardin Botanique National de Belgique, Meise: 116 p.
Vujnovic K. & Wein R.W. (1997) The biology of Canadian weeds. 106. Linaria dalmatica
(L.) Mill. Can. J. Plant Sci. 77: 483-491. [available online at: http://stoppinginvasives.com/dotAsset/75742cf6-71af-4e52-a31d-1d008ef5d8df.pdf]