Phylogenetic interpretation of light and electron microscopic features of selected members of the phylogroup Moewusinia (Chlorophyceae), with new generic taxonomy

In molecular phylogenetic trees of zoospore-producing unicellular chlorophycean algae, well-resolved lineages often do not correspond to current taxonomic categories, and therefore characterising diagnostic morphological traits of lineages can be challenging. We employed a phylogenetic framework to examine the evolution of light microscopic (LM) and transmission electron microscopic (TEM) features in the phylogroup Moewusinia and a related genus and then assessed the features that could be used to diagnose lineages. Most LM characters were homoplasies, but particular character states uniquely supported lineages. Autospores arranged in isobilateral tetrads made up a suitable generic feature; whereas, tetrahedral tetrads or indefinite groups of autospores were not. Some chloroplast phenotypes lacked phylogenetic signal, especially the sponge-like form previously used to define genera. Pyrenoid types characterised clades at different depths. TEM features of zoospores (i.e. papillar shape, cell wall layers, nuclear position and components of the basal apparatus) were generally consistent with clades. The sawhorse-shaped distal connecting fibre with beam-like extensions was characteristic of some phylogroups. Ultrastructural components of sexual reproduction may serve as a marker at deeper phylogenetic depths. Within Moewusinia, the saline habitat was restricted to one clade. In total, nine phylogenetic clades were defined at generic rank using phenotypic traits. Three new genera were proposed: Eubrownia gen. nov., with the new combinations E. aggregata, E. dissociata, E. illinoisensis and E. isobilateralis; Parachlorococcum turfosum gen. & sp. nov.; and Alvikia gen. nov., with the new combination Al. littoralis. Chlorococcum (Cc.) was emended, with the new combinations Cc. aerium, Cc. macropyrenoidosum and Cc. vacuolatum. Tetracystis with the type species T. aeria was abandoned. Spongiococcum was emended with the new combination S. aplanosporum.