Phylogenetic position of the Oocystaceae (Chlorophyta)

The complete 18S rRNA gene sequences of three Ootystis A. Braun species (Oocystaceae) and three other chlorococcal algae, Tetrachlorella alternans (G. M. Smith) Kors. (Scenedesmaceae), Makinoella tosaensis Okada (Scenedesmaceae), and Amphikrikos cf, nanus (Fott & Heynig) Hind. (Chlorellaceae) were determined and subjected to four different phylogenetic analysis algorithms. Independent of the reconstruction method, these taxa clustered together as a monophyletic group (Oocystaceae) within the Trebouxiophyceae. This result was supported by high bootstrap values. A comparison of morphological data with the phylogenetic reconstructions indicated that the evolution of Oocystaceae was accompanied by a reduction in the number of plastids, This study fully supports the taxonomic assignment of the Oocystaceae as a distinct family. The diacritic criterion that the cell walls are composed of several cellulose layers with perpendicular fibril orientations is in accordance with the molecular data.