Taxonomic re‐evaluation of two species of Hypnea (Cystocloniaceae, Rhodophyta) from the Mexican tropical Pacific, and description of Hypnea ixtapaensis sp. nov.

SUMMARY Hypnea species are distributed across tropical, subtropical, and temperate regions. They exhibit high intraspecific morphological variation, which complicates species delimitation based solely on morphological characteristics. Recently, molecular analyses have enabled the validation of numerous species, the identification of cryptic species, and the description of new taxa. In the present study, morphological and anatomical analyses (36 characters), along with the molecular markers rbcL and COI‐5P, were used to reevaluate the taxonomic identity of two Hypnea species frequently reported on the tropical Pacific coast of Mexico: Hypnea pannosa and H. spinella . Our study, based on morphological and molecular evidence, confirmed the presence of H. pannosa with its typical morphology of a great cushion‐shaped thallus of short axes and branches and identified an undescribed species characterized by erect, free branches. Our results suggest that H. spinella is not present along the Mexican tropical Pacific coast and that previous records should be considered misidentifications. We propose and describe this new species as Hypnea ixtapaensis sp. nov.