Life-history variation in Rhodophysema elegans (Palmariales, Rhodophyta) from the North Atlantic and crustose Rhodophysema spp. from the North Pacific

Abstract

Two life histories have been established for Rhodophysema elegans from the North Atlantic Ocean by field and culture studies. These are entirely distinct and occur, respectively, in (i) sexual, tetrasporangial and (ii) asexual, bisporangial populations. In tetrasporangial isolates, a sexual life history was unequivocally indicated by chromosome numbers of n = 18 in vegetative cells and 18 pairs during meiotic tetrasporocyte division. Bisporangial plants, interpreted as polyploid gametophytes (2x = 36), undergo a direct, mitotic bispore to bisporophyte life history and also produce diploid spermatia. The sexual life history in North Atlantic R. elegans differed in several respects from that reported in a Californian isolate. A taxonomic study of crustose Rhodophysema species from the Pacific Ocean in comparison with type material of R. elegans from France indicated that two entities have been reported from Pacific North America under this name, but neither corresponds with the type. (i) Crusts epiphytic on the seagrass Phyllospadix and algal fronds are identified as Rhodophysema odonthaliae, described from Japan. Evidence of both sexual and direct, mitotic tetrasporangial life histories has been observed in field collections of this species, (ii) Larger plants, with much larger spermatangia, collected on pebbles and brown algal stipes are considered as being growth forms of the monostromatic Californian species Rhodophysema minus.