Xanthium L.
Xanthium is a taxonomically very complex genus (especially subgenus Xanthium). Two different taxonomic philosophies have been proposed: Widder (1923) recognized more than 20 species whereas Anglo-Saxon taxonomists tend to reduce the number of species to 2 or 3 (Sell & Murrell 2006, Strother 2006). Wisskirchen (1995) provided a more or less intermediate taxonomic framework. Since we have experienced that the separation of species within the subgenus Xanthium is very critical (even between Xanthium orientale and X. strumarium) we have chosen to apply the most recent New World taxonomy (i.e. Strother 2006).
Recent molecular studies, however, shed new light on the genus (Tomasello 2018). Five species are recognized worldwide: X. ambrosioides and X. spinosum on the one hand, and X. strumarium, X. orientale and X. chinense (X. pungens) on the other. The identity of the plants found in Belgium needs to be re-assessed, although the only naturalized species doubtlessly belongs to X. orientale.
The origin of the genus Xanthium is also unclear. Xanthium strumarium (s.str.) is usually claimed as an Old World species but this seems rather unlikely, the rest of the genus being native to the New World. Tomasello (2018) demonstrated that X. strumarium s.str. indeed is from the Old World while the other species are from the Americas.
- Leaf base with a 3-parted spine. Leaves tapered at both ends, usually pinnately lobed. Bur 10-12 mm long === Xanthium spinosum
- Leaf base without spines. Leaves broadly ovate, sometimes shallowly lobed, long-petiolate. Bur 10-30 mm long === X. strumarium
References
Adema F. & Jansen M.T. (1979) Xanthium L. in Nederland. Gorteria 9: 300-303. [available online at: http://www.repository.naturalis.nl/document/567878]
Clement E.J. (1981) Cockleburs in Britain. BSBI News 29: 13.
Hardtl H. (1973) Über die Inhaltsstoffe einiger Xanthium-Arten. Phyton 15(1-2): 1-25.
Hicks A.J. (1972) Systematic studies of Xanthium (Compositae: Ambrosieae); the Cockleburs of Tazewell County, Illinois. Diss. Abstr. Int. B 32(10): 5649-5650.
Hicks A.J. (1975) Short Notes. Apomixis in Xanthium? Watsonia 10: 414-415.
Jeanmonod D. (1998) Xanthium subg. Xanthium et Helichrysum italicum, deux cas taxonomiques ardues. Candollea 53(2): 435-457.
Lambinon J., Delvosalle L., Duvigneaud J. (avec coll. Geerinck D., Lebeau J., Schumacker R. & Vannerom H.) (2004) Nouvelle Flore de la Belgique, du Grand-Duché de Luxembourg, du Nord de la France et des Régions voisines (Ptéridophytes et Spermatophytes). Cinquième édition. Jardin botanique national de Belgique, Meise: CXXX + 1167 p.
Löve D. & Dansereau P. (1959) Biosystematic studies on Xanthium. Canad. J. Bot. 37: 173-208.
Sell P. & Murrell G. (2006) Flora of Great Britain and Ireland. Vol. 4 Campanulaceae – Asteraceae. Cambridge University Press, Cambridge: XXVIII + 624 p.
Shukla B., Prao G.P. & Gupta S.N. (1988) Systematic position of Xanthium: a chemosystematic approach. Proc. Nation. Acad. Sci. India B 58(1): 81-86.
Strother J.L. (2006) Xanthium. In: Flora of North America Editorial Committee (eds.), Flora of North America, vol. 21. Oxford University Press, New York-Oxford: 19-20.
Tomasello S. (2018) How many names for a beloved genus? - Coalescent-based species delimitation in Xanthium L. (Ambrosiinae, Asteraceae). Mol. Phyl. Evol. 127: 135-145.
Widder F.J. (1923) Die Arten der Gattung Xanthium. Feddes Repert., Beihefte 20: 1-221.
Widder F.J. (1925) Übersicht über die bisher in Europa beobachteten Xanthium-Arten und Bastarde. Feddes Repert. 44: 273-305.
Wisskirchen R. (1989) Zur Verbreitung und Kennzeichnung von Xanthium saccharatum Wallr. em. Widder an Rhein und Mosel. Decheniana 142: 29-38.
Wisskirchen R. (1995) Verbreitung und Ökologie von Flussufer Pioniergesellschaften (Chenopodion rubri) im mittleren und westlichen Europa. Diss. Bot. 236. Cramer, Berlin-Stuttgart.