Although thalli attributable to the genus Sorella (Delesseriaceae, Rhodophyceae) can be easily recognized, determination of species is difficult. The characters described for differentiating the type species are found to vary and overlap when numerous specimens are examined. Attempts to correlate morphological aspects with environmental variables (e.g., depth, substrate, light, temperature, or season) were unsuccessful. When plants typical of each of the California species were grown in the laboratory under a series of different light and temperature regimes each maintained its distinctiveness. Development of reproductive structures, vegetative growth rates, and a Polysiphonia-typs life history are described from cultured plants. It is suggested that non-pinnate variants, whether broad or narrow, be referred to S. delicatula: all specimens of this species were of the size described for var. californica. Pinnately branched, often but not always relatively broad, thalli with either paired or median spermatangial sori are treated as S. pinnata.