The life-history of Acrosymphyton purpuriferum from the Mediterranean is heteromorphic diplohaplontic. Carpospores grew into creeping plants much resembling the species Hymenoclonium serpens (Cm.) Batt. The Hymenoclonium phase produced tetrahedral tetrasporangia the tetraspores of which grew into Acrosymphyton gametophytes. Short day conditions induced the formation of the tetrasporangia. The Hymenoclonium phase could reproduce itself vegetatively by 4-celled structures resembling seriate tetrasporangia. The induction of these structures did not show any relationship to temperature or daylength.