Morphology, reproduction and range extension of Rhodogorgon (?Nemaliales, Rhodophyta)

Abstract

Originally described from the Caribbean, the genus Rhodogorgon J. Norris et Bucher (?Nemaliales, Rhodophyta) is reported from the subtidal of the Philippines for the first time. Gametophytes are multiaxial, dioecious and have cellulosympodial development. Carpogonia, which have not been reported previously, are sessile and, after supposed fertilization, fuse with the supporting cell of the carpogonium. The mature carposporophyte is diffuse and consists of linked clusters of pseudodichotomously branched gonimoblast filaments. Carposporangia are terminal and regenerate such that nests of persistent carposporangial walls are formed. Monosporangia are formed in gametangial plants from the apices of filaments and also regenerate repeatedly within old sporangial walls. In culture, carpospores develop to form small filamentous tufts with sessile monosporangia. Ecological observations in the Caribbean indicate that plant height and branch density in Rhodogorgon is related to the degree of water movement and it is proposed that R. carriebowensis J. Norris et Bucher be placed in synonymy with R. ramosissima, which was separated on the basis of length and density of branches. It is proposed that Rhodogorgon be placed in a more broadly defined Nemaliales to include the Acrochaetiaceae and those genera presently assigned to the Batrachospermales.