Culture studies of a sexual life history inMyriotrichia clavaeformis(Phaeophyceae, Dictyosiphonales)

The life history of Myriotrichia clavaeformis from western Ireland was studied in culture. Zoids from unilocular sporangia of field sporophytes developed to microthalli. In long days, these functioned as dioecious gametophytes which produced isogametes in plurilocular gametangia. In short days, the microthalli formed morphologically identical asexual zoids. Both asexual zoids and unfused gametes could germinate and develop to gametophytes. Zygotes, in contrast, immediately gave rise to sporophytic macrothalli, starting with the formation of an upright filament terminated by a hair. Large zoids from plurilocular sporangia on the sporophyte reproduced this generation directly. Sporophytes in culture also formed unilocular sporangia, releasing meiospores which re-established the gametophyte generation. Chromosome numbers are n = 12 and 2n = 24. The culture results are used to model the phenology of M. clavaeformis.