Euphorbia brittingeri Opiz ex Samp. (syn.: E. flavicoma DC. subsp. verrucosa (Fiori) Pignatti) (W, C and S-Eur.) – A very rare, mostly ephemeral but locally naturalized alien. Known since 1973 from Couvin and subsequently regularly confirmed, for instance in 1996 by Duvigneaud (1997). See also www.waarnemingen.be (still present in abundance in 2013). In Couvin Euphorbia brittingeri grows in calcareous grassland under Pinus nigra and was probably introduced with the latter from northeastern France (Duvigneaud l.c.). By now the pine wood grew tall and Euphorbia brittingeri is now confined to the southern slope of the wood margin. Exceptionally seen elsewhere, for instance in a newly sown road verge in the port of Antwerpen in 1998.
Euphorbia brittingeri is very characteristic in having densely tuberculate capsules. However, confusion is still likely with native Euphorbia dulcis and alien E. oblongata. In the former tubercles are evidently cylindrical (ca. twice as long as wide; more or less spherical or only slightly longer than wide in both other species) and cyathial glands ultimately purplish (not yellowish-green). Euphorbia oblongata only has 2-3 cyathial glands instead of 4 in both other species.
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Selected literature:
Duvigneaud J. (1997) Euphorbia brittingeri (= Euphorbia verrucosa) est toujours présent à Couvin. Adoxa 17: 6.