The author studied the morphology of Blackstonia perfoliata s.l. and compared its variability with that of the other representatives of the genus. She also carried out ecological studies of “ Blackstonia perfoliata ssp. serotina” ssp. on the Dutch island Voome and compared her results with those in the literature relating to B. perfoliata in some adjacent regions, notably the Upper Rhine area. On morphological and ecological grounds B. perfoliata ssp. per foliota and ssp. serotina are to be regarded as two distinct species, B. perfoliata and B. acuminata.