The present treatment constitutes a taxonomic study of the benthic marine red algae known in the northern Gulf of California. In all, 387 species of Rhodophyta belonging to two subphyla were found: the Rhodophytina, represented by 2 classes, 2 orders, 2 families, 7 genera, and 14 species; and Eurhodophytina, represented by 2 classes, 5 subclasses, 19 orders, 47 families, 133 genera, and 373 species (including varieties, forms, and possible new species); 71 species of red algae (~18%) are endemic to the Gulf of California. Together with the 133 species of Chlorophyta and Phaeophyceae, 520 marine algae are known in the northern Gulf. The systematic account includes the presently accepted taxon name, descriptions of the subphyla, classes, orders, families, genera, and species, with keys and illustrations to aid in their identification. Along with the taxon name are its basionym, synonyms, author(s), date and place of valid publication, type locality, relevant taxonomic studies, description, habitat, and distribution in the Gulf of California and, if applicable, in the eastern, central, and/or western Pacific. A remarks section includes information on taxonomy, nomenclature, ecology, distribution extensions and new records, and/or other problems or facts of interest. A new genus, 1 new subgeneric section, and 8 new species are described; 30 new combinations are proposed (listed in Appendix 1). A new name, Rhodymenia huertae, is chosen to replace an illegitimate name; a lectotype illustration is selected for Laurencia paniculata Kutzing; 15 previously reported species are considered uncertain records; and 3 species are excluded from the Gulf’s marine flora.—Norris, James N. Marine Algae of the Northern Gulf of California II: Rhodophyta. Smithsonian Contributions to Botany, number 96, xvi + 555 pages, 236 figures, 2014.