Rhizoclonium ramosum sp. nov. (Cladophorales, Chlorophyta), a new freshwater algal species from China

Abstract

A novel freshwater filamentous green alga was collected from rocks situated in flowing water in Henan and Hunan provinces, central China. This alga was slender and soft and exhibited similar morphology to that of Rhizoclonium spp. It was attached to the substrate by rhizoids, and had parietal, reticulate chloroplasts. However, it exhibited true branches characteristic, from the basal to the apical parts of the filaments. There were a large number of nuclei (4–17) per cell. Two types of pyrenoids (bilenticular and, rarely, zonate) were observed using light microscopy and transmission electron microscopy. Phylogenetic analyses were mainly based on small subunit and large subunit rDNA sequences. Both morphological and phylogenetic analyses indicated that this alga should be classified under Rhizoclonium. The results of our culture and morphological comparisons supported the presence of true branches in Rhizoclonium. Thus, we proposed this alga as a new species, Rhizoclonium ramosum sp. nov. Moreover, the present study emphasizes that the cell diameter, length/cell diameter (L/D) ratio, nuclear number, and the presence of rhizoidal laterals are the key characteristics of the genus Rhizoclonium.