In this study, more species of Oedogoniales had been introduced by our wide range of sample collection and culture. The species analysed in this investigation had covered all the three genera of the Oedogoniales, and the number of species in each genus was over two to guarantee the feasibility of monophyletic analysis of the genus.
The two sequences, 18S rDNA and 28S rDNA, have been analyzed respectively or united and the results showed that the monophyletic clade Oeodgoniales was situated in a comparatively divergent position in the Chlorophyceae; the genus Oedocladium, as a separated clade, was clustered within the clade of Oedogonium; whereas the genus Bulbochaete was in a comparatively divergent position to the other two genera with a location basally in the Oeodgoniales.
We firstly obtained the rbcL gene sequences. The results of the analyses based on these sequences make us believe that the Oedogoniales may considered to be a member of the earliest group of the class with some other filiform green algae, and they are better to be regarded as an unique order of the Chlorophyceae. And within the Oedogoniales, the Bulbochaete is more complex than the other two genera, and it as well as the Oedocladium are suggested to have been derived from a Oedogonium or Oedogonium-like ancestor.
The relationship among the species of Oedogonium was discussed, focusing on ITS-2 phylogeny analyzed combining with some morphological characteristics, and the CBC analyse was also performed. The results supported the Jao’s hypothesis that the type of sexual differentiation should be the criterion for classification below the rank of genus Oedogonium from the view of molecular phylogeny. And furthermore, the evolution nexus from the monoecious to the dioecious nannandrous and then to the dioecious macrandrous taxa was supposed by this analyse.