Liagorothamnion mucoides gen. et sp nov (Ceramiaceae, Rhodophyta) from the Caribbean Sea

A new genus and species, Liagorothamnion mucoides Huisman, Ballantine & Wynne (Ceramiaceae, Rhodophyta), is described from the Caribbean Sea. Thalli are mucilaginous and filamentous and generally have one indeterminate lateral branch and 1-4 whorl-branchlets per axial cell. Spermatangia are borne on whorls of fertile branchlets on 3-16 successive axial cells. Carpogonial branches are 3-4-celled and borne on a periaxial supporting cell that also bears two or more sterile groups. Lower cells of the carpogonial branch also bear lateral cells. Following presumed fertilization, the carpogonium cuts off short connecting filaments that fuse with the basal cells of whorl-branchlets on the fertile axial cell (which therefore function as auxiliary cells) but not with the supporting cell. Gonimolobes arise from the auxiliary cells and, when mature, are composed entirely of carposporangia. The carposporangia are quadripartite when mature. Tetrasporangia are unknown. The new genus appears to have affinities with the tribe Dohrnielleae but differs from all known genera in a number of unusual features, justifying a new tribe, Liagorothamnieae, to accommodate it. In contrast to virtually all members of the Ceramiaceae, the supporting cell of the carpogonial branch of Liagorothamnion bears two sterile cell groups, which appear to provide nutrition for the postfertilization processes. This feature is found, however, in members of the other families included in the Ceramiales (Rhodomelaceae, Delesseriaceae, Dasyaceae) and could indicate that Liagorothamnion represents the primitive condition for this character in the Ceramiaceae.