Cylindraxis rotundatus gen. et sp. nov. and its generic relationships within the Liagoraceae (Nemaliales, Rhodophyta)

Abstract

Cylindraxis rotundatus gen. et sp. nov. is described from the Perth and Geraldton regions of Western Australia. Plants are composed of terete, lubricous axes encompassing a continuous hollow cylinder of calcification at the border of the medulla and cortex. Gametophytes are monoecious and produce cystocarps typical of the Liagoraceae, but are characterized by the following unique features: carpogonial branches are primarily 4-celled (occasionally 3-celled), the basal cells always having the general shape and staining properties of vegetative inner cortical cells; a maximum of two (occasionally only one) gonimolobes is produced from the distal half of the transversely divided fertilized carpogonium; the gonimoblast initial and the innermost one to three cells of the gonimolobes become spherical and enlarge conspicuously during early carposporophyte development. Other significant features of the monotypic genus are the laxly filamentous gonimoblasts that grow directly toward the thallus surface, and the synchronously maturing gonimolobes that begin production of carposporangia on breaching the outer cortex. No subsidiary sterile filaments of any kind are associated with the cystocarp, and a fusion cell is not formed. Cladistic analysis of the 15 genera of the Liagoraceae points to the distinctiveness of Cylindraxis and suggests that the group is not naturally divisible into separate families, subfamilies or tribes. It is speculated that evolutionary progression within the family has likely been from precursors with features still displayed by genera such as Trichogloeopsis and Liagoropsis to genera such as Liagora, Helminthocladia, Cumagloia and Dermonema.