Eleven new taxa are described from California; two species, in addition, have new varieties added to them; and two species are given new circumscriptions to include a number of entities previously known under other names. New species are described in Percursaria (Chlorophyta), in Feldmannia (Phaeophyta), and in eight genera (Membranella, Porphyra, Rhododiscus, Peyssonelia, Prionitis, Blinksia, Besa and Rhodoglossum) of Rhodophyta. Two monotypic genera of Rhodophyta are described for the first time. One, Membranella nitens, is added to the Bangiales, and the other, Blinksia californica, is the type for a new family, the Blinksiaceae (Gigartinales). Half of the species of red algae are crustose non-corallinaceous species.