Phylogenetic position of the Oedogoniales within the green algae (Chlorophyta) and the evolution of the absolute orientation of the flagellar apparatus

The order Oedogoniales is made up of green algae with an unusual form of cytokinesis, a ring of flagella on the zoids, and a complex sexual reproduction. The genera included in this order, Oedogonium, Oedocladium and Bulbochaete, differ in their type of habit. In this contribution we report a phylogenetic analysis using 18S ribosomal DNA sequences from 66 species of green algae, including ten species of Oedogonium isolated from fresh water bodies in Argentina. The phylogenetic study demonstrates the monophyly of the Oedogoniales within the green algae, and suggests that in this group the flagellar apparatus of the stephanokont zoid could have derived from a DO configuration. It is also found that the genus Oedogonium does not appear to be monophyletic and that the morphological characters traditionally used for the taxonomic classification of Oedogonium species do not define natural groups.