Morphology and phylogenetic relationships of the CW group of the unicellnlar green algae

In the molecular phylogenetic investigation on the terrestrial, unicellular green algae having basal bodies arranged in clockwise orientation, which have been classified in the four orders, it was found that they were included in a monophyletic group (CW group). The morphological characters which have been assumed to be important in classification were evaluated on the basis of the present molecular phylogeny. The tetrad and sarcinoid formations of vegetative cells, which were once considered as features of the order Chlorosarcinales appeared in different clades, and thus, the opinion that these features could not be used for classification at the order rank was supported. Multinucleate conditions of vegetative cells developing with age evolved in different subclades within the CW group. An asteroid chloroplast was found in different clades, and it was pointed that morphological observation for identifying should be careful, because this type of chloroplast is often confused with axile and parietal ones. A net-like or sponge-like chloroplast was found in a clade, in which both mutinuleate and uninucleate organisms were included in it's subclades, resulting that these chloroplast types occurred as synapomorphy. The morphological features of zoospores, such as presence or absence of cell wall around cell body, and composition of cell wall layers, were synapomorphy in some subclades. The flagellar lengths, direction of flagella, and compositions of flagellar apparatus were also characters shared in several specified subclades. Accumulation of astaxanthin appeared in two clades as synapomorphy, and organisms having motile and non-motile vegetative cells were included in one of these subclades. In habitats other than soil environment, sea water inhabitants were placed in a monophyletic branch, showing that they secondarily developed from an organism lived in freshwater regions. Unicellular green algae fixing on substrates in freshwater environment were found to evolved in several different phylogenetic lineages. A symbiotic alga within leaves of Lemna trisulca was placed in a branch comprising organisms having similar morphology of vegetative cells and zoospores to this symbiont.