AbstractLamella margins ofPolytriehadelphusfrom throughout the range of the genus have been examined by SEM. All specimens clearly referable on other characters to the genus have characteristically crenate lamella margins covered with angular flakes of epicuticular wax. In this respect they resemble species ofDawsoniabut differ from all other Polytrichaceae examined. The lamella margin characters are useful for critical identification of non-fruiting plants ofPolytriehadelphusfrom other vegetatively similar Polytrichaceae. They confirm thatP. erieoidesand the North AmericanP. lyalliiMitt. do not belong to this genus.Polytriehadelphushas a trans-Pacific and essentially Southern Hemisphere distribution extending from Sulawesi and New Guinea through New Zealand and the Fuegian region to the northern Andes, with a north-western outpost in Costa Rica. It is likely that this distribution is derived from a continuous Antarctic range in the late Cretaceous, and that much of the radiation of the genus at the two northern ends of its present range took place in the mid to late Tertiary. Outlying stations on Tristan da Cunha and the Marquesas probably result from long-distance dispersal.