139 Taxonomic Re-Examination of Eight Species of Nitella (Charales, Charophyceae) from Asia, And Phylogenetic Relationships Within the Genus Based on rbcL and Atpb Gene Sequences

Eight taxa of Nitella, collected from Asia, were investigated using LM and SEM of the oospores and sequencing of rbc L gene to improve understanding of their taxonomic status. Our SEM observations demonstrated that the oospore morphology of six taxa – N. capitulifera (= N. acuminata f. capitulifera ), N. japonica (= N. furcata f. japonica ), N. tumulosa (= N. furcata f. tumulosa ), N. megaspora comb. nov. (= N. pseudoflabellata f. megaspora ), N. gracillima (= N. gracilis f. gracillima ), and N. axilliformis (= N. translucens f. axilliformis ) – is distinctly different from that of the species to which R.D. Wood assigned them as infraspecific taxa. Our rbc L sequence data showed that N. japonica is separated phylogenetically from N. furcata , N. tumulosa from N. furcata , N. megaspora from N. pseudoflabellata , and N. axilliformis from N. translucens . In addition, to re-examine the taxonomic system of Nitella proposed by R.D. Wood, who treated oospore wall ornamentations as a diagnosis at the infraspecific level, we carried out molecular phylogenetic analyses using the combined sequence dataset for atpB and rbc L genes of these eight species, as well as twelve species of Nitella previously studied. The combined sequence data resolved five robust clades within the subgenus Tieffallenia that were characterized by differences in oospore wall ornamentation. However, the species and sectional diagnoses of R.D. Wood, such as the form and cell number of dactyls in vegetative thalli, were variable within the clades. Therefore, R.D. Wood's taxonomic system appears unnatural, at least within the subgenus Tieffallenia .