The tropical environment of the Hawaiian Islands is associated with abundant and diverse terrestrial and subaerial algae. Representatives are known from multiple lineages of algae, including the cyanobacteria, green algae, red algae, diatoms, and xanthophytes, and numerous (putative) endemic species have been described from these members of the Hawaiian algal flora in recent years. Members of two Hawaiian lineages of the green algal Class Ulvophyceae, Spongiochrysis hawaiiensis and Pseudorhizoclonium spp., represent particularly interesting case studies of the transition to a terrestrial lifestyle in the Archipelago. Described in 2006, Spongiochrysis hawaiiensis is a green-to-golden colored unicellular or pseudofilamentous alga that is a prominent member of coastal tree bark biofilm communities on the windward sides of the Hawaiian Islands. Phylogenetic analyses resolve the sister taxon of this lineage as a marine cladophoralean alga. Similarly, two closely related species of the newly described cladophoralean genus Pseudorhizoclonium are being described from the Hawaiian Islands (one endemic); again, phylogenetic analyses suggest that the terrestrial lifestyle of these two species may be most recently derived from marine lineages. These examples provide support for evolutionary transitions by algae from marine to terrestrial habitats, without a freshwater transition phase .