The algae of El Salvador have received limited attention. We combined collections from the mangroves of El Salvador and neighboring southern Mexico, and used culture studies and molecular analysis to gain insights into the diversity in this poorly explored region. Bostrychia montagnei , Caloglossa apomeiotica , and Caloglossa ogasawaraensis were newly recorded in El Salvador. Bostrychia montagnei has not been reported from the Pacific Americas before. B. montagnei normally produced axial cells with two-tier cells, typical of the species, but sometimes a series of axial cells had three-tier cells. This was a significant tier cell number variation not previously seen in Bostrychia species. Bostrychia montagnei had a Polysiphonia -type sexual life history with both unisexual and bisexual gametophytes. Caloglossa apomeiotica isolates in culture from El Salvador and Chiapas, Mexico, either had a normal sexual life history or asexual recycling of tetrasporophytes. Those found in El Salvador were the first record of C. apomeiotica south of Jalisco, Mexico, a distance of 1200 km. Four strains isolated from El Salvador and Chiapas, Mexico, which were morphologically part of the Caloglossa leprieurii sensu lato lineage, were analyzed; however, they were not closely related to any named species, indicating that this is a new species that will require further study.