Abstract Cephalozia macrostachya Kaal. in Britain and Ireland is revised, and two infraspecific taxa are recognized at varietal rank. Heteroecious plants of C. macrostachya var. spinijlora (Schiffn.) Mull. Frib. are readily separated from the dioecious var. macrostachya by 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 of C. macrostachya which was based on collections of both forms from a single locality in Norway. The edentate male bracts of var. macrostachya were overlooked, and when C. spinijlora was subsequently established the distinctions between the two constituent t...