The identity of Trentepohlia algae (Chlorophyta: Trentepohliales) from Point Lobos State Reserve and the S. Francisco region, California.

Terrestrial chlorophyte algae of the order Trentepohliales are found in humid habitats around the world. Although most diverse and abundant in the tropics, on a global scale the group is nearly cosmopolitan. The most distinctive macroscopic trait of the Trentepohliales is their orange, golden, or red color, which is due to the accumulation of carotenoid pigments. Orange algae of the genus Trentepohlia, the most species-rich genus in the order, can be found growing on trees, rocks, and other substrates along the Pacific Coast of the United States, including the San Francisco Bay area. Perhaps the best known site for these algae is at Point Lobos State Reserve in Carmel, CA. The orange algae at this site are often referred to by California naturalists as‘‘Trentepohlia aurea’’ or ‘‘Trentepohlia aurea var. polycarpa’’. Given the challenges in identifying species in this genus and some confusion about nomenclature, we sampled Trentepohlia at Point Lobos and elsewhere in the region to clarify the identity of these algae. We confirm that the Trentepohlia at Point Lobos (and most of the Trentepohlia we sampled at other sites) are T. flava, which was long considered to be a form of T. aurea and was often reported under the heterotypic synonym T. aurea var. polycarpa Trentepohlia abietina was the only other species recorded and our observations suggest the possibility that in this region the two species exhibit different substrate preferences (T. flava generalist on many different substrates, T. abietina limited to tree bark).