A sexual life history in Rhodophysema (Rhodophyceae): a re-interpretation

Abstract

Previous studies of field collected and cultured plants of Rhodophysema from different localities have demonstrated the existence of tetrasporangial and male plants, whereas female plants were apparently absent. Re-investigation of R. elegans from California in culture indicates that structures on tetrasporangial crusts previously interpreted as ‘hair cells’ are carpogonia. The fertilized carpogonium (zygote) divides into a stalk cell (tetrasporangial mother cell) and a tetrasporangium. The contents of the sporangium divides to produce four tetraspores, whereas the stalk cell produces successive tetrasporangia. A carposporophyte is lacking. The vegetative tissue of the crust is not sporophytic, as previously supposed, but is gametophytic, with spermatia and carpogonia produced on the same crust. This life history is the most reduced of all those known in sexually reproducing red algae. The position of the carpogonium—terminal on a vegetative filament rather than on a specialized branch—and the production of successive tetrasporangia by a stalk cell lead us to propose that Rhodophysema belongs to the Palmariales rather than the Cryptonemiales.