Taxonomic re-examination of a Chinese strain labeled 'Eudorina sp.' (Volvocaceae, Chlorophyta) based on morphological and DNA sequence data

SUMMARY A culture strain, CCFA 646, originating from the People's Republic of China and designated as ‘Eudorina sp.’ in the Culture Collection of Freshwater Algae at the Institute of Hydrobiology, Chinese Academy of Sciences, was re-examined taxonomically based on light and electron microscopy and molecular phylogenetic analyses. Vegetative colonies of CCFA 646 were sub-spherical or ovoid and contained 16 or 32 cells of identical size. The cells had a cup-shaped chloroplast with a single basal pyrenoid. During asexual reproduction, each daughter colony developed within a transparent vesicle inside the parental colony. Under the electron microscope, the vegetative colony exhibited a tripartite colonial boundary of the extracellular matrix. Inside the boundary, each cell was tightly enclosed by a dense fi-brillar layer of the matrix (cellular envelope). These morphological characteristics suggested that CCFA 646 is assignable to Eudorina unicocca G. M. Smith or Ya-magishiella unicocca (Rayburn et Starr) Nozaki. In addition, 1128 base pairs of the large subunit of ribulose-1, 5-bisphosphate carboxylase/oxygenase (rbcL) gene were sequenced from CCFA 646 and NIES-578 of Y. unicocca. Phylogenetic trees were constructed based on these sequence data as well as on the previously published rbcL gene sequences from five strains of Y. unicocca, six strains of four Eudorina species and 28 related species. The sequence data suggested with high bootstrap values that CCFA 646 and all six strains of Yama-gishiella form a monophyletic group positioned outside the large monophyletic group comprising Eudorina, Pleo-dorina and Volvox (except for sect. Volvox). Therefore, CCFA 646 can be assigned to Y. unicocca, which has not previously been reported from P. R. China.