Morphology, taxonomy, and nomenclature of three species of Hawaiian green algae (Chlorophyta) are examined. Udotea? abbreviata Gilbert is shown to be incorrectly placed in that genus and more appropriately allied to Pseudochlorodesmis. The complex nomenclatural relationships of Cladophora tildeniae Brand in Tilden, Cladophora tildeniae Brand, and Cladophora hawaiiana Tilden are described, with the latter deemed the appropriate name and Microdictyon japonicum var. laxum Gilbert regarded as a synonym. An examination of Cladophoropsis luxurians Gilbert has shown it to have delayed formation of transverse walls at the bases of lateral branches, a feature not consistent with inclusion in Cladophoropsis but rather with Cladophora. The new combinations Pseudochlorodesmis abbreviata (Gilbert) Abbott & Huisman and Cladophora luxurians (Gilbert) Abbott & Huisman are made, and nine species of marine benthic Chlorophyta are newly recorded for the Hawaiian Islands.