Observations on the Genus Rhodymenia Grev. (Rhodophyta, Rhodymeniales) in the California Islands

The natural history of four sympatric species of red seaweeds in the genus Rhodymenia Greville (R. californica Kylin, R. pacifica Kylin, R. callophyllidoides Hollenberg & Abbott and R. arborescens Dawson) was investigated in the course of subtidal surveys at 68 sites in the eight California Islands. Despite their broad latitudinal range, these cool-temperate species are ecologically specialized, being restricted to deep-water or habitats characterized by upwelling, currents or oceanic swell in southerly latitudes. The four species can be distinguished by their local distributions and phenological patterns. Rhodymenia californica and R. pacifica have the broadest latitudinal and vertical ranges. Fertile plants occur most frequently in the subtidal, with tetrasporophytes more common than fertile gametophytes. While R. californica is fertile throughout the year, R. pacifica is probably winter fertile. Rhodymenia callophyllidoides is strictly subtidal, has a narrower latitudinal distribution and a very different pattern of reproduction, with fertile plants common and abundant throughout the year. Rhodymenia arborescens, also subtidal, has the most limited distribution and has been collected the least. It is at the northern end of its range in California and may be more common in deeper waters to the south.