Euphorbia heterophylla L. (syn.: Poinsettia heterophylla (L.) Klotzsch et Garcke) (S-Am.) – A very rare and ephemeral alien. First seen on the unloading quay of the Cargill plant at the Kanaaldok in the port of Antwerpen in 1997 (Verloove & Vandenberghe 1998). In 2000 also recorded on sandy waste ground at the Ghent Grain Terminal in the port of Gent. Both records were obviously associated with soybean waste. In 2018 a 1.5 m tall, flowering and fruiting individual was seen in a garden in Ruiselede where it was apparently introduced as impurity in bird food.
Euphorbia heterophylla – now more or less a pantropical weed – is very reluctant to flower in Belgium (mostly non-flowering plants have been observed up to present). It best resembles Euphorbia dentata (both probably cross when found together; see Dressler 1961) but it is less hairy and its leaves are more finely serrate to subentire and often very heteromorphous on a same plant. Moreover, its leaves are all alternate. E. cyathophora is also similar. The latter has leaves that are at least in part reddish and very different involucral glands. In E. heterophylla these typically are stipitate with round opening (vs. sessile and oblong opening).
Selected literature:
Dressler R.L. (1961) A synopsis of Poinsettia (Euphorbiaceae). Ann. Missouri Bot. Gard. 48(4): 329-341. [available online at: https://www.biodiversitylibrary.org/item/54726#page/356/mode/1up]
Oliveira A.S. & Sá-Haiad B. (1988) Estudos taxonômicos sobre a familia Euphorbiaceae Juss.: 1. Euphorbia heterophylla L. e Euphorbia cyathophora Murr. Sellowia 40: 5-31.
Turner I.M. (1999) Euphorbia heterophylla and E. cyathophora (Euphorbiaceae) in the Malay Peninsula. Gard. Bull. Singapore 51(1): 99-102.
Verloove F. & Vandenberghe C. (1998) Nieuwe en interessante voederadventieven voor de Belgische flora, hoofdzakelijk in 1997. Dumortiera 72: 18-36.