Molecular phylogeny, systematics, and revision of the type species of <italic>Lobomonas</italic>,<italic> L. francei</italic> (Volvocales, Chlorophyta) and closely related taxa.

In the present study, three new strains of the rare volvocalean green alga <italic>Lobomonas</italic> were isolated from field‐collected samples, one from Sardinia (Italy) and two from Argentina, and comparatively studied. The Sardinian and one of the Argentinian strains were identified as <italic>Lobomonas francei</italic>, the type species of the genus, whereas the second Argentinian strain corresponded to <italic>L. panduriformis</italic>. Two additional nominal species of <italic>Lobomonas</italic> from culture collections (<italic>L. rostrata</italic> and <italic>L. sphaerica</italic>) were included in the analysis and shown to be morphologically and molecularly identical to the <italic>L. francei</italic> strains. The presence, number, and shapes of cell wall lobes, the diagnostic criterion of <italic>Lobomonas</italic>, were shown to be highly variable depending on the chemical composition of the culture medium used. The analyses by SEM gave evidence that the cell wall lobes in <italic>Lobomonas</italic> originate at the junctions of adjacent cell wall plates by extrusion of gelatinous material. The four <italic>L. francei</italic> strains had identical nrRNA gene sequences and differed by only one or two substitutions in the ITS1 + ITS2 sequences. In the phylogenetic analyses, <italic>L. francei</italic> and <italic>L. panduriformis</italic> were sister taxa; however, another nominal <italic>Lobomonas</italic> species (<italic>L. monstruosa</italic>) did not belong to this genus. <italic>Lobomonas</italic>, together with taxa designated as <italic>Vitreochlamys</italic>,<italic> Tetraspora</italic>, and <italic>Paulschulzia</italic>, formed a monophyletic group that in the combined analyses was sister to the “<italic>Chlamydomonas</italic>/<italic>Volvox</italic>‐clade.” Based on these results, <italic>Lobomonas</italic> was revised, the diagnosis of the type species emended, a lectotype and an epitype designated, and several taxa synonymized with the type species. [ABSTRACT FROM AUTHOR]