Euphorbia amygdaloides L. subsp. robbiae (Turrill) Stace (syn.: E. robbiae Turrill, E. amygdaloides var. robbiae (Turrill) Radcliffe-Smith) (NW-Turkey) – A very rare but probably increasing escape from cultivation. First seen from discarded garden waste by a railway siding in Roeselare in 2000 and 2001 (soon destroyed afterwards). Further seen in the city of Oudenaarde in 2005 (cracks in pavement close to a plantation). Probably the only stable and obviously long-naturalized population is located in the Buylaers nature reserve in Lokeren.
This taxon is rather frequently cultivated nowadays and possibly overlooked (as a result of confusion with subsp. amygdaloides) or merely neglected.
Records of subsp. amygdaloides outside of its native Belgian distribution area and/or in non-natural or disturbed habitats are suspect and require confirmation. In addition to subsp. robbiae another close relative from Turkey is also cultivated in Europe: Euphorbia oblongifolia (C. Koch) C. Koch (see Carter & Cullen 1997 for its separation).
Can L., Erol O., Challen G. & Küçüker O. (2012) On the rediscovery of Euphorbia amygdaloides subsp. robbiae and its type. Turk. J. Bot. 36: 650-654. [available online at: http://journals.tubitak.gov.tr/botany/issues/bot-12-36-6/bot-36-6-4-1110-18.pdf]
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. (1997) Can Euphorbia robbiae be revived? B.S.B.I. News 76: 58-60.
Palmer J.R. (1985) A spurge worth looking out for. BSBI News 40: 26-27.
Palmer J.R. (1997) Euphorbia robbiae alive and well (at least in the home counties)., BSBI News 77: 53-54.
Radcliffe-Smith A. (1976) The mystery of Euphorbia robbiae (Euphorbiaceae). Kew Bull. 30(4): 697-698.
Stace C.A. (1989) New combinations in the British and Irish flora. Watsonia 17: 442-444.
Stearn W.T. (1973) Mrs Robb and 'Mrs Robb's bonnet' (Euphorbia robbiae). J. Roy. Hort. Soc. 98(7): 306-310.
Turrill W.B. (1953) Euphorbia robbiae. Curtis’s Botanical Magazine 169: 208.