Morphological and molecular evidence reveals three new species of <i>Gelidium</i> (Gelidiaceae, Rhodophyta) for the southern Mexican Tropical Pacific

Abstract The genus Gelidium is a representative element of the Mexican Tropical Pacific. The recent use of molecular tools has allowed us to resolve the taxonomic problems of some species and to increase the knowledge regarding this group of red algae in the region. The present study aimed to evaluate specimens collected in the southern Mexican Tropical Pacific using molecular markers and morphological characters. Samples were collected from four locations along the coast of Oaxaca state. They were characterised morphologically and molecularly using rbc L and COI–5P. Phylogenetic analysis classified the examined specimens into three independent clades, representing taxonomic entities different from what has been described previously for the genus. With the support of morphological data and genetic distances, we propose three new species for the Mexican Tropical Pacific: Gelidium dawsonii sp. nov., Gelidium longisporophyllum sp. nov., and Gelidium rubruparvum sp. nov. Some of the distinct characteristics of these species are based on little size of G. rubruparvum , the branching pattern of G. longisporophyllum and G. dawsonii , the number of layers of medullary cells in G. dawsonii and G. rubruparvum , and the tetrasporangial sorus in G. longisporophyllum . We also highlight the relationship between Asian and Mexican species and the value of using different tools in the evaluation of the taxonomic status of the genus Gelidium .