Euphorbia dentata Michaux s.l. (syn.: Poinsettia dentata (Michaux) Klotzsch et Garcke; incl. E. davidii Subils) (N- and C-Am.) – A rare and always ephemeral alien. First recorded in 1986 in the port of Gent (three specimens; Robbrecht & Jongepier 1989). Subsequently observed twice at the Ghent Grain Terminal at the Rodenhuizedok (in 1996 and 1999), most probably as a soybean alien (single specimens). Finally also recorded as a birdseed alien on a dump in Rumbeke-Roeselare in 2003 and on the verge of an unloading quay near a grain mill in the port of Roeselare in 2004.
Euphorbia dentata is a rather variable species and sometimes reluctant to flower. In flower it is best distinguished by its flowers with only one cyathial gland (characteristic of section Poinsettia). In the vegetative phase Euphorbia dentata is a weedy, hairy, erect annual with coarsely dentate, ovate, often spotted leaves.
The taxonomy of Euphorbia dentata is still under study and poorly understood. Some authors tend to recognize several closely related species (with a different ploidy level). One of these, Euphorbia davidii (Subils 1984), seems to be the usual agricultural weed (very common, for instance, in the wheat belt of the United States; comm. M. Mayfield). Genuine Euphorbia dentata is said to be merely a garden weed. Both species are morphologically very similar and pending further research Euphorbia dentata is here accepted in a wide sense as to include, among others, E. davidii. Belgian plants (rarely with mature seeds) have an indumentum of predominantly short, retrorse hairs and probably belong to the latter.
Selected literature:
Barina Z., Shevera M., Sîrbu C. & Pinke G. (2013) Current distribution and spreading of Euphorbia davidii (E. dentata agg.) in Europe. Centr. Eur. J. Bot. 8(1): 87-95.
Geltman D.V. (2012) American species Euphorbia davidii Subils (Euphorbiaceae) in the flora of East Europe and the Caucasus. Turczaninowia 15(1): 37-39. [available online at: http://ssbg.asu.ru/turcz/turcz_15_1_37-39.pdf]
Girerd B. & Roux J.-P. (2007) Nouveautés 2006 pour la flore vauclusienne. Bull. Soc. Bot. Vaucluse 17: 4-6.
Hoffer-Massard F. (2011) Euphorbia davidii Subils, une nouvelle espèce pour la Suisse? Bulletin du Cercle vaudois de botanique 40: 93-94. [available online at: http://doc.rero.ch/lm.php?url=1000,43,42,20120306164756-QR/14-Hoffer-Euphorbia_davidii.pdf]
Marchessi J.E., Subils R., Scaramuzzino R.L., Crosta H.N., Eseiza M.F., Saint André H.M. & Juan V.F. (2011) Presencia de Euphorbia davidii Subils (Euphorbiaceae) en la Provincia de Buenos Aires: morfología y anatomía de la especie. Kurtziana 36(1): 45-53.
Oprea A., Barina Z. & Sîrbu C. (2012) Euphorbia davidii Subils (Euphorbiaceae) – an alien species new to the Romanian flora. Contr. Botan. 47: 7-12. [available online at: http://reviste.ubbcluj.ro/contributii_botanice/materiale/2012/Contrib_Bot_vol_47_pp_007-012.pdf ]
Pinke G., Molnár S., Garamvölgyi V. & Barina Z. (2012) The first occurrence of Euphorbia davidii in Hungary. Növényvédelem 48(3): 117-120.
Robbrecht E. & Jongepier J.-W. (1989) De synantrope flora van het havengebied van Gent (België, Oost-Vlaanderen), waarnemingen van 1986 tot 1988. Dumortiera 44: 1-12.
Subils R. (1984) Una nueva especie de Euphorbia sect. Poinsettia (Euphorbiaceae). Kurtziana 17: 125-130.
Vladimirov V. & Petrova A.S. (2009) A new alien species of Euphorbia (Euphorbiaceae) to the Bulgarian flora. Phytol. Balcan. 15(3): 343-345. [available online at: http://www.bio.bas.bg/~phytolbalcan/PDF/15_3/15_3_06_Vladimirov_&_Petrova.pdf]