Symphyotrichum lanceolatum (Willd.) Nesom (syn.: S. simplex (Willd.) Á. Löve et D. Löve, Aster lanceolatus Willd., A. simplex Willd., A. lanceolatus subsp. simplex (Willd.) A.G. Jones) (N-Am.) – A rather commonly naturalized escape from cultivation or garden throw-out. Already known from the valley of river Vesdre before 1835. At present more or less widely distributed but apparently most concentrated around Brussels and in the valley of river Maas (Verloove 2006). Symphyotrichum lanceolatum is usually found in man-made habitats, often on damp, nitrophilous soils: disused railway yards, urban waste land, road verges and off-ramps. However, it also occurs in more or less natural, riparian vegetation, for instance along river Maas (Verloove 2002). In such habitats Symphyotrichum lanceolatum often forms dense, nearly monospecific stands and is considered an invasive alien. It is unknown if Symphyotrichum lanceolatum produces viable seed in Belgium. It probably always reproduces from rhizomes. Additional information on its invasive behavior in Belgium is available here: http://ias.biodiversity.be/species/show/137.
In its native distribution range Symphyotrichum lanceolatum is a very variable species (Brouillet & al. 2006). As a rule, Belgian populations are rather uniform and are characterized by distinctly unequal, narrow involucral bracts, nearly glabrous stems (especially below; hairy in lines near apex), heads usually not congested and rather narrow leaves that are reduced in size in the inflorescence. Such plants correspond well with var. lanceolatum, although other varieties might also occur (see for instance Sell & Murrell 2006). Populations with pure white, smaller ligules have been ascribed to Symphyotrichum tradescantii (L.) Nesom (syn.: Aster tradescantii L.) (see for instance Adema 1983, Hoffman 1996) but this surely does not hold true. Genuine Symphyotrichum tradescantii is a rather local, delicate species. It is a caespitose (not colonial) perennial and unsuitable for cultivation as an ornamental.
Symphyotrichum lanceolatum differs from S. xsalignum by predominantly whitish outer involucral bracts (only midrib green) being less than ½ the length of the inner. Moreover, it most frequently has white ligules (more rarely pinkish) and (sub-) entire leaves. Symphyotrichum xsalignum, on the contrary, has nearly greenish involucral bracts (only margins white) that are subequal in length (outer more than ½ as long as inner), it rarely (if ever) has white ligules and evenly toothed leaf margins. Remarkably, in France the latter is much more widespread than S. lanceolatum (Tison & de Foucault 2014).
Further study may lead to the recognition of additional, poorly understood species (see Dirkse & al. 2014).
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Selected literature:
Adema F. (1983) Drie kleinbloemige Aster-soorten in Nederland. Gorteria 8(11): 194-195.
Adolphi K. (1995) Neophytische Kultur- und Anbaupflanzen als Kulturflüchtlinge des Rheinlandes. Nardus 2: 272 p.
Brouillet L., Semple J.C., Allen G.A., Chambers K.L. & Sundberg S.D. (2006) Symphyotrichum. In: Flora of North America Editorial Committee (eds.), Flora of North America, vol. 20. Oxford University Press, New York-Oxford: 465-539.
Chmielewski J.G. (1992) Inter-relationships among cytotype and achene characteristics in Aster lanceolatus Willd. (Asteraceae). Beitr. Biol. Pfl. 66(1): 69-84.
Chmielewski J.G. & Semple J.C. (1983) The cytogeography of Aster lanceolatus: 3. Cytoecology in southern Ontario. Canad. J. Bot. 61(7): 1879-1886.
Chmielewski J.G. & Semple J.C. (2001) The biology of Canadian weeds. 113. Symphyotrichum lanceolatum (Willd.) Nesom (Aster lanceolatus Willd.) and S. lateriflorum (L.) Löve & Löve (Aster lateriflorus (L.) Britt.). Canad. J. Pl. Sc. 81: 829-849. [available online at: http://pubs.aic.ca/doi/pdf/10.4141/P00-056]
Dirkse G.M., Reijerse A.I. & Duistermaat L. (2014) De ontrafeling van in Nederland ingeburgerde Amerikaanse herfstasters (Symphyotrichum Nees. subg. Symphyotrichum sect. Symphyotrichum, Asteraceae). Gorteria 37: 1-24.
Feher A. (2007) Historical reconstruction of expansion on non-native plants in the Nitra River Basin (SW Slovakia). Kanitzia 15: 47-62. [available online at: http://www.bdtf.hu/ttk/blgi/nov/Kanitzia/Kanitzia%2015.%20%282007%29%20V.%20%2847-62.%20old.%29.pdf]
Hoffman M.H. (1996) Die in Zentraleuropa verwilderten und kultivierten nordamerikanischen Astern. Feddes Repert. 107(3-4): 163-188.
Jedlicka J. & Prach K. (2006) A comparison of two North-American asters invading in central Europe. Flora - Morphology, Distribution, Functional Ecology of Plants 201(8): 652-657.
Milanovic Đ, Maslo S & Šaric Š. (2018) Four neophytes new for the flora of Bosnia and Herzegovina. Botanica Serbica 42(1): 139-146. [available online at: http://botanicaserbica.bio.bg.ac.rs/arhiva/pdf/2018_42_1_709_full.pdf]
Nešić M., Obratov-Petković D., Skočajić D., Bjedov I. (2013) Seed quantity and quality in fruit heads of Aster lanceolatus Willd.: Implications for invasion success. Bulletin of the Faculty of Forestry 108: 129-144. [available online at: http://www.doiserbia.nb.rs/img/doi/0353-4537/2013/0353-45371308129N.pdf]
Northridge R. (2003) Aster lanceolatus Willd. and A. x salignus Willd. in Co Fermanagh (H33). Irish Nat. J. 27(8): 326.
Obratov-Petković D., Bjedov I., Radulović S., Skočajić D., Đunisijević-Bojović D. & Đukić M. (2009) Ecology and distribution of an invasive species Aster lanceolatus Willd. on wet habitats in Belgrade (in Serbian). Glasnik Sumarskog fakulteta 100: 159-178. [available online at: http://www.doiserbia.nb.rs/img/doi/0353-4537/2009/0353-45370900159O.pdf]
Sell P. & Murrell G. (2006) Flora of Great Britain and Ireland. Vol. 4 Campanulaceae – Asteraceae. Cambridge University Press, Cambridge: XXVIII + 624 p.
Semple J.C. (1979) The cytogeography of Aster lanceolatus (synonyms A. simplex and A. paniculatus) in Ontario with additional counts from populations in the United States. Canad. J. Bot. 57(4): 397-402.
Semple J.C. & Brammall R.A. (1982) Wild Aster lanceolatus X lateriflorus hybrids in Ontario and comments on the origin of A.ontarionis (Compositae-Astereae). Canad. J. Bot. 60(10): 1895-1906.
Semple J.C. & Chmielewski J.G. (1987) Revision of the Aster lanceolatus complex, including A. simplex and A. hesperius (Compositae: Astereae): a multivariate morphometric study. Canad. J. Bot. 65: 1047-1062.
Semple J.C., Chmielewski J.G., Rao K.S. & Allen G.A. (1983) The cytogeography of Aster lanceolatus: 2. A preliminary survey of the range including A. hesperius. Canad J. Bot. 61(2): 434-441.
Tison J.-M. & de Foucault B. (coord.) 2014) Flora Gallica. Flore de France. Editions Biotope, Mèze : xx + 1196 p.
Verloove F. (2002) Ingeburgerde plantensoorten in Vlaanderen. Mededeling van het Instituut voor Natuurbehoud n° 20: 227 p.
Verloove F. (2006) Aster lanceolatus. In: Van Landuyt W., Hoste I., Vanhecke L., Van den Bremt P., Vercruysse W. & De Beer D., Atlas van de flora van Vlaanderen en het Brussels gewest. Instituut voor Natuur- en Bosonderzoek, Nationale Plantentuin van België en Flo.Wer: 168-169.