AbstractCephalozia macrostachyaKaal. in Britain and Ireland is revised, and two infraspecific taxa are recognized at varietal rank. Heteroecious plants ofC. macrostachyavar.spinijlora(Schiffn.) Müll. Frib. are readily separated from the dioecious var.macrostachyaby their distinctive androecia, typically with dentate bracts and welldeveloped bracteoles, and also by their failure to develop. perianths and sporophytes. There are slight morphological differences in the leaves of the two varieties, but the only reliable vegetative distinction is provided by differences in the width of the gemmae. Both varieties are widely distributed in Britain and Ireland. The recent lack of recognition of two segregates is traced back to the original description ofC. macrostachyawhich was based on collections of both forms from a single locality in Norway. The edentate male bracts of var.macrostachyawere overlooked, and when C. spinijlora was subsequently established the distinctions between the two constituent taxa ofC. macrostachyasensu lato were incompletely characterised.C. macrostachyais lectotypified. Further studies are required on developmental abnormalities in the gametangia of var. spinijlora.