AbstractSeasonal patterns of reproductive development are reported for the five British mossesAtrichum undulatum, Bryum argenteum, Grimmiapulvinata, Polytrichum alpestreandTortula muralis, and vegetative phenology is also described forB. argenteumandP. alpestre. Clearly defined seasonal cycles of gametangial and sporophytic development characterize P. alpestre, and the cycles in Britain resemble those previously reported for polar populations of this species. The seasonal timing of the later stages of sporophytic development, and of spore release, was shown to be relatively constant within each species but the gametangial cycles and fertilization periods appear to be more variable than inP. alpestrein the weedy colonist,B. argenteum, and particularly in the lithophytes,G. pulvinataandT. muralis.