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



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Taxonomic name: 
Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith