Phylogenetic position of the Oocystaceae (Chlorophyta)

The complete 18S rRNA gene sequences of three Ootystis A. Braun species (Oo cystaceae) and three other chlorococcal algae, Tetrachlorella alternans (G. M. Smith) Kors. (Scenedesmaceae), Makinoella tosaensis Okada (Scenedesmace ae), and Amphikrikos cf, nanus (Fott & Heynig) Hind. (Chlorellaceae) were d etermined 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 resul t was supported by high bootstrap values. A comparison of morphological dat a with the phylogenetic reconstructions indicated that the evolution of Ooc ystaceae was accompanied by a reduction in the number of plastids, This stu dy fully supports the taxonomic assignment of the Oocystaceae as a distinct family. The diacritic criterion that the cell walls are composed of severa l cellulose layers with perpendicular fibril orientations is in accordance with the molecular data.