<i>Gracilaria liaoi</i> sp. nov. (Gracilariales, Rhodophyta) from the Philippines

Abstract Previous molecular studies have split species of foliose Gracilaria that were presumed to be widespread into species complexes. The recurrent discrepancies in taxonomy of Gracilaria vieillardii , a species widely reported in the Indo-Pacific and Australasian waters, prompted the use of morpho-histological and molecular approaches to resolve these outstanding issues. Material from the Philippines, initially presumed to be conspecific with G. vieillardii , was earlier shown to be genetically distinct, warranting species distinction. This material also enabled us to describe similar Philippine materials whose species criteria, satisfying morpho-anatomical and molecular support, merit recognition of a newly described species, Gracilaria liaoi . Our phylogenetic analyses revealed that G. liaoi formed a strongly supported clade distinct from authentic G. vieillardii from New Caledonia and other Gracilaria species. Characteristic features of G. liaoi include a broader blade, the presence of marginal spines in the basal regions, and numerous nutritive filaments encompassing the cystocarp cavities. There is still plenty of scope for fieldwork to establish the possible extent of the distribution of G. liaoi , and explore other aspects of the biology of this species. The present status of specimens referable to ‘ G. vieillardii ’ in the Philippines and elsewhere should be re-examined.