Taxonomic notes on Herposiphonia vietnamica (Rhodophyta, Ceramiales)

Taxonomic features of the red alga Herposiphonia vietnamica Pham (Ceramiales, Rhodomelaceae) are described on the basis of material collected from its type locality, Phu Quoc Island, Vietnam. This species is characterised by relatively slender (50-120 µm wide) prostrate axes with a small number of pericentral cells (eight to 10 per segment), short (300-700 µm high and consisting of seven to 11 segments), slender (50-100 µm wide) and terete determinate branches, tetrasporangia arranged in a straight series of two to five, an ovoid cystocarp (380-420 µm high and 280-320 µm wide) that is lateral on a determinate branch and relatively large in comparison with the thallus size, and three to five, spiralled spermatangial branches that lack a sterile tip.