Some cumophytic Rhodomelaceae (Rhodophyta) occurring in Hawaiian surf

Abstract Small algae belonging to the Rhodomelaceae occur on boulders exposed to Hawaiian surf. Two genera from this very rigorous environment, Alsidium and Fernandosiphonia, are described for the first time from the Hawaiian Islands, and two new species, Aisidium cymatophilum and Fernandosiphonia ecorticata, are erected. Two other species of Fernandosiphonia are also recorded for Hawai'i, F. hancockii comb. nov., previously recognized as a species of Polysiphonia in Baja California and Hawai'i, and F. nana, recently described from north-eastern Australia. Alsidium cymatophilum and some forms of Fernandosiphonia ecorticata have setose erect axes, a habit apparently well adapted to the surf environment. Both species have specialized attachment systems that are successful in strong surf, A. cymatophilum forming an extensive crust on the rock surface from which erect axes arise, and F. ecorticata having firmly attached prostrate axes that produce erect branches. The other two species of Fernandosiphonia are ...