Aster L.
Recent morphological and cytological research has considerably modified the generic boundaries of the genus Aster (Nesom 1994). All but two of the Belgian representatives of the genus Aster s.l., native as well as non-native, are now accommodated in several other genera. An alphabetical overview is given below:
Aster amellus L. => Aster amellus L.
Aster brachyactis S.T. Blake => Symphyotrichum ciliatum (Ledeb.) Nesom
Aster divaricatus L. => Eurybia divaricata (L.) Nesom
Aster lanceolatus Willd. => Symphyotrichum lanceolatum (Willd.) Nesom
Aster lateriflorus (L.) Britton => Symphyotrichum lateriflorum (L.) Á. et D. Löve
Aster linosyris (L.) Bernh. => Galatella linosyris (L.) Reichenb. f.
Aster novae-angliae L. => Symphyotrichum novae-angliae (L.) Nesom
Aster novi-belgii L. => Symphyotrichum novi-belgii (L.) Nesom
Aster pilosus Willd. => Symphyotrichum pilosum (Willd.) Nesom
Aster racemosus S. Elliott => Symphyotrichum racemosum (S. Elliott) Nesom
Aster sedifolius L. => Galatella sedifolia (L.) Greuter
Aster subulatus Michaux s.l. => Symphyotrichum subulatum (Michaux) Nesom s.l.
Aster xsalignus Willd. => Symphyotrichum xsalignum (Willd.) Nesom
Aster tripolium L. => Tripolium pannonicum (Jacq.) Dobrocz.
Aster xversicolor Willd. => Symphyotrichum xversicolor (Willd.) Nesom (incl. A. laevis L. => Symphyotrichum laeve (L.) Á. et D. Löve)
Aster s.str. now includes ca. 180, mainly Eurasian species. Even in this new circumscription Aster is both paraphyletic and polyphyletic (Li & al. 2012). Some species are cultivated as ornamentals, two of which have been recorded as escapes in Belgium. Both are distinguished from Symphyotrichum by their phyllaries that are obtuse at apex. Species of Aster s.str. seem to naturalize much less easily and are rarely (if ever) invasive.
1 Phyllaries (involucral bracts) 1,5-3 mm wide. Involucre 8-13 mm high. Heads 25-75 mm across === Aster amellus
Phyllaries less than 1,5 mm wide. Involucre 5-6 mm high. Heads up to 25 mm wide === A. ageratoides
Literature:
Adolphi K. (1995) Neophytische Kultur- und Anbaupflanzen als Kulturflüchtlinge des Rheinlandes. Nardus 2: 272 p.
Chen Y.L., Brouillet L. & Semple J.C. (2011) Aster. In: Wu Z.Y. & Raven P.H. (eds.), Flora of China, vol. 20–21. Science Press, Beijing & Missouri Botanical Garden Press, St. Louis: 574-632. [available online at: http://www.efloras.org/florataxon.aspx?flora_id=2&taxon_id=102902]
Grierson A. (1964) A revision of the Asters of the Himalayan area. Notes from the Royal Botanic Garden, Edinburgh 26: 67-163.
Hawke R.G. (2013) A Comparative Study of Cultivated Asters. Plant Evaluation Notes 36: 1-11. [available online at: http://www.chicagobotanic.org/downloads/planteval_notes/no36_asters.pdf]
Hetterscheid W.L.A. & van den Berg R.G. (1996) Cultonomy of Aster L. Acta Bot. Neerl. 45(2): 173-181.
Hoffman M.H.A. (1995) Aster (1). Dendroflora 32: 6-23.
Jones A.G. & Young D.A. (1983) Generic concepts of Aster (Asteraceae): a comparison of cladistic, phenetic and cytological approaches. Syst. Bot. 81: 71-84.
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.
Li W.-P., Yang F.-S., Jivkova T. & Yin G.-S. (2012) Phylogenetic relationships and generic delimitation of Eurasian Aster (Asteraceae: Astereae) inferred from ITS, ETS and trnL-F sequence data. Ann. Bot. 109(7): 1341-1357. [available online at: http://aob.oxfordjournals.org/content/early/2012/04/18/aob.mcs054.full.pdf]
Nesom G.L. (1994) Review of the taxonomy of Aster sensu lato (Asteraceae: Astereae), emphasizing the New World species. Phytologia 77: 141-297.
Nesom G.L. (2020) The genus Aster (Asteraceae) in the strictest sense. Phytoneuron 2020-56: 1–22. [available online at: http://www.phytoneuron.net/2020Phytoneuron/56PhytoN-Asteramellus.pdf]
Sell P. & Murrell G. (2006) Flora of Great Britain and Ireland. Vol. 4 Campanulaceae – Asteraceae. Cambridge University Press, Cambridge: XXVIII + 624 p.
Shaw J. (2014) The splitting of Aster. The Plantsman N.S. 13(2): 120-125. [available online at: https://www.rhs.org.uk/about-the-rhs/publications/magazines/The-Plantsman/2014-issues/june/the-splitting-of-aster]
Thellung A. (1913) Die in Mitteleuropa kultivierten und verwilderten Aster- und Helianthusarten nebst einem Schlüssel zur Bestimmung derselben. Allg. Bot. Zeitschr. 19: 87-89, 101-112, 132-140.
Yeo P.F. (2000) Aster. In: Cullen J. & al. (eds.), The European Garden Flora, vol. 6. Cambridge University Press, Cambridge: 570-578.