Life history and hybridization studies on Gigartina stellata and Petrocelis cruenta (Rhodophyta) in the North Atlantic [Algae]

Two basic types of life history were found among these isolates: a direct-type life history involving the formation of further foliose plants from carpospores, some isolates of which also form spermatangia on the same papillae as the cystocarps; and a heteromorphic-type in which only crustose plants resembling Petrocelis cruenta are formed from carpospores. The results from crossing experiments with 32 male and 27 female isolates of the heteromorphic-type derived from both G. stellata and P. cruenta showed that two virtually non-interbreeding populations with a high degree of geographical separation exist in the north-eastern Atlantic. Morphological differences between plants from each population are described. On the basis of culture and crossing results, Petrocelis cruenta J. Agardh is placed in synonymy with Gigartina stellata (Stackhouse in Withering) Batters.