SUMMARYAt its northernmost distributional limit in northeastern America, in Newfoundland,Bryopsis hypnoidesLamour. appears to have a heteromorphic, monophasic life‐history. Zygotes resulting from fusion of anisogametes develop in culture into prostrate filamentous germlings, these also reproducing sexually by anisogametes to form a new generation of the prostrate type. ErectBryopsislater grew from the prostrate phase: asexual stephanokontic zooids were entirely absent. The life‐history in Newfoundland compares in part with that forB. hypnoidesfrom northern parts of its European range; the presence of sexual reproduction in the prostrate phase in Newfoundland, however, is unique inBryopsisand is not apparently a temperature dependent phenomenon. In the field NewfoundlandB. hypnoidesreaches sexual maturity in winter at temperatures less than 0°C. Germling phases studied in culture could not be located in the field. The question is raised as to the possible genetic isolation of NewfoundlandB. hypnoidesfrom populations in Eu