Euphorbia oblongata Griseb. (SE-Eur.) – A very rare alien, most probably an escape from cultivation. A single plant of Euphorbia oblongata was discovered in woodland in Roeselare (Sterrebos) in 2008 (later confirmed but now gone). It grew in half-shade by a ditch. Its origin is obscure: the Sterrebos is an old park (with, among others, long-established populations of Euphorbia dulcis and Trachystemon orientalis) but E. oblongata appears to be a recent, independent introduction. Since 2011 a small population of Euphorbia oblongata also persists by river Schelde in Eine (Oudenaarde). This species is, surprisingly, not mentioned by Carter & Cullen (1997) and Jäger & al. (2008) although a garden origin seems most likely.
Euphorbia oblongata is a poorly known species (see also Barrett 1996). It is one of the few species with 2(-3) cyathial glands (4 in nearly all widespread species in Eurasia). It furthermore usually has densely pubescent stems (although nearly glabrous forms also exist).
Similar plants have been recorded by a ditch in Brugge around 2000 but the population was destroyed soon afterwards (and voucher specimens are lacking).
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Selected literature:
Barrett D. (1996) Euphoria oblongata Griseb. in S.E. Hampshire (v.c. 11). BSBI News 71: 46-48.
Carter S. & Cullen J. (1997) Euphorbia. In: Cullen J. & al. (eds.), The European Garden Flora, vol. 5. Cambridge University Press, Cambridge: 81-101.
Clement E.J. (1979) Adventive news: 14. Euphorbia oblongata Griseb. in Britain. BSBI News 22: 16-17.
Jäger E.J., Ebel F., Hanelt P. & Müller G. (eds.) (2008) Rothmaler Band 5. Exkursionsflora von Deutschland. Krautige Zier- und Nutzpflanzen. Springer Verlag, Berlin: 880 p.
Petch C.P. (1979) Euphorbia oblongata. BSBI News 23: 26.