CROSSABILITY BETWEEN HAWAIIAN AND JAPANESE POPULATIONS OF AHNFELTIOPSIS-CONCINNA (GIGARTINALES, RHODOPHYTA)

Hawaiian and Japanese populations of the red alga Ahnfeltiopsis concin na (J. Agardh) Silva et DeCew (Phyllophoraceae, Gigartinales) were exa mined on the basis of cultured plants. Reported differences between Ha waiian and Japanese plants in two taxonomically significant reproducti ve features, the absence or presence of a sterile lateral on the carpo gonial branch and the non-nemathecial or nemathecial tetrasporangial s orus, were not found. Plants of both populations formed procarps, each of which consisted of a large supporting cell and a three-celled carp ogonial branch (carpogonium, hypogynous cell, and basal cell) with a o ne-celled sterile lateral from the basal cell, and nemathecial tetrasp orangial sori. Furthermore, no morphological differences between cultu red plants of the Hawaiian and Japanese populations were found. All at tempted crosses were positive, with carpospores from the cross develop ing into fertile F-1 tetrasporophytes releasing tetraspores that devel oped into dioecious F-1 gametophytes, the female gametophytes of which formed normal cystocarps, indicating that interbreeding is potentiall y free among the populations studied. It is concluded that the Hawaiia n and Japanese plants are referred to as a single species that shows r emarkable variability in gross morphology which may be caused by growt h stages and different environments.