Trentepohlia brevicellulis comb. et stat. nov. (Trentepohliaceae, Ulvophyceae) found in Japan

The family Trentepohliaceae contains many common aerial algae, most widely distributed, particularly in tropical and subtropical regions. Eight species of the genus Trentepohlia have been reported in Japan. We report another taxon, Trentepohlia brevicellulis (Cribb) S. Handa and H. Tsubota comb. et stat. nov., growing on bark in western Honshu, Japan. This alga was previously described as Trentepohlia bosseae var. brevicellulis Cribb. However, the relationship between the bosseae and brevicellulis varieties of T. bosseae could not be ascertained owing to the lack of genetic information for brevicellulis. Therefore, we aimed to examine the detailed morphological characteristics of brevicellulis in wild samples and cultured strains and to review the taxonomy, including systematic information obtained by genetic analysis. Its phylogenetic position was resolved based on 18S rDNA sequence data. It differs from T. bosseae and its variety samoensis in exhibiting a warty zoosporangium surface, an unthickened septum with no central pit field, and a non-rusty-brown cell wall. The four key characteristics of T. brevicellulis include a warty layer on the inner surface of the non-bent side of the suffultory cell wall, an ostiole located near the base of the zoosporangium, curved tapering filaments with thickened cell walls, and globular vegetative spores in the basal portion of the filament. Transmission electron microscopy revealed a pit field wherein simple plasmodesmata were present in the septum. Phylogenetic analysis suggested that this alga and T. bosseae form distinct clades and that T. brevicellulis is separate from T. bosseae. Thus, our study helped redefine the accurate taxonomic position of the species under study as Trentepohlia brevicellulis (Cribb) S. Handa and H. Tsubota comb. et stat. nov., a clade distinct from T. bosseae and reported for the first time in Japan.