The morphology and life history of Acrochaetium polyblastum (Rosenv.) Børg. and Acrochaetium hallandicum (Kylin) Hamel (Rhodophyta, Nemaliales)

The morphology of two species of Acrochaetium, provisionally identified as A. polyblastum (Rosenv.) Borg, and A. hallandicum (Kylin) Hamel, is described in some detail. They are shown to be tetrasporophyte and gametophyte respectively in the same life history. Both phases are characterized by the possession of a stellate chromatophore with a central pyrenoid; the tetrasporophyte has a spore which germinates septately and subsequently develops a multicellular filamentous base, the gametophyte has a unicellular base. The sexual cycle is mainly temperature-controlled, the gametangia being formed under higher temperature than the tetrasporangia. Both generations reproduce asexually by means of monospores, in a wide temperature range. The morphological variability, as affected by different environmental conditions, appears to be very large; moreover there is an ample variation between different clones grown under uniform conditions. General structure of the plant, the type of spore germination in each phase, and cell diameter are the most reliable characters in delimiting the species from other acrochaetioid taxa. The life histories of Acrochaetium species possessing stellate chromatophores, as exemplified by a number of different species now, show a remarkably uniform pattern, as far as alternation of morphological phases is concerned. It is suggested that characters of the total life history provide a reasonable basis for the systematics of the acrochaetioid algae.