A recent molecular phylogenetic study inferred from chloroplast-encoded rbcL sequence analyses based on twenty specimens of Gracilariopsis Dawson 1949 worldwide confirmed the monophyly of the genus and revealed the existence of three new Caribbean species (Gurgel et al., J. Phycol., submitted). Gracilariopsis sp. 1 collected in the Mexican Gulf of Mexico is sister to G. tenuifrons. G. sp. 2 collected in Caribbean Panama (Colón City) and Venezuela (Paraguana Península) is morphologically closely related to G. panamensis. G. sp. 3 collected in Venezuela (La Vela de Coro) is distinct from all other terete and stringy species that characterize the genus by being a flat-foliose taxon; it also shows a basal topology with uncertain phylogenetic relationship to an undetermined species from Japan and China and to G. heteroclada from the Philippines. The lack of clear-cut vegetative and reproductive features among the species coupled with a high degree of thallus plasticity may account for the fact that genetically distinct species were not previously recognized as taxonomically distinct. Our molecular and morphological studies reveal that the diversity of Gracilariopsis species in the western Atlantic and probably in the rest of the world is currently underestimated. Morphologicaly detailed descriptions for all three new species are provided.

Key words: algae, Gracilariaceae, Gracilariopsis, phylogeny, rbcL, Rhodophyta