Systematics of Rhizoclonium-like algae (Cladophorales, Chlorophyta) from Japanese brackish waters, based on molecular phylogenetic and morphological analyses

Abstract

Ichihara K., Shimada S. and Miyaji K. 2013. Systematics of Rhizoclonium-like algae (Cladophorales, Chlorophyta) from Japanese brackish waters, based on molecular phylogenetic and morphological analyses. Phycologia 52: 398–410. DOI: 10.2216/12–102.1Analyses of partial small subunit (SSU) and large subunit (LSU) rRNA genes of Rhizoclonium-like filamentous green algae, collected from brackish waters in Japan, revealed the existence of five genetically distinct species. Four species (Rhizoclonium spp. 1–4) were closely related to Rhizoclonium hieroglyphicum. The phylogenetic position of the Rhizoclonium-like sp. 5 remained largely unresolved, although LSU analyses suggested a relationship with Chaetomorpha ligustica. Rhizoclonium spp. 1 and 4 were identified as Rhizoclonium riparium and Rhizoclonium lubricum, respectively. Rhizoclonium spp. 2 and 3 were morphologically distinguishable from other Rhizoclonium species and minute Chaetomorpha species. Rhizoclonium sp. 2 exhibited a characteristically small L/D (cell length/cell diameter) ratio and large number of nuclei (3–7 per cell), while Rhizoclonium sp. 3 was characterized by unique spindle or band-like, densely arranged chloroplasts; therefore, we described them as new species, Rhizoclonium breve and Rhizoclonium confertum. Rhizoclonium-like sp. 5 was characterized by perforated chloroplasts and polypyramidal pyrenoids and was clearly distinct from known Rhizoclonium or Chaetomorpha species. Based on the phylogenetic position and morphological features of Rhizoclonium-like sp. 5, we described it as a new species of Chaetomorpha, Chaetomorpha tokyoensis.