Abstract:

Coccoid green algae primarily refers to algae that are solitary living organisms spherical or ellipsoid in shape. It is widely distributed around the world living in freshwater, seawater and subaerial habitats. The similarity in shape of these organisms hides a huge cryptic biodiversity. Coccoid green algae phylogeny belongs primarily to four orders and some incertae sedis taxa of two classes. This paper reports the changes in taxonomic study methods of coccoid green algae and the resulting cryptic biodiversity that has been discovered. A total of 15 new genera (now totaling 40 genera for coccoid green algae) and 12 new combinations were discovered from collected specimens. This paper focuses on the discovery and renaming of coccoid green algae in Trebouxiophyceae and Chlorophyceae after 1998. We present the diagnostic features, phylogenic changes and reasons for the discoveries and remaining. The changes in the genera of Chlorella and Scenedesmus are presented in details. We also discuss the application of DNA-based methods in taxonomic identification of coccoid green algae and how differences in phylogenetic position have become the main basis for taxonomic identifaction. Finally, we address the problems in phylogenic studies of coccoid green algae by which taxonomic location based on the morphological features have not yet been validated by phylogenetic methods. In the future, algae taxonomists should combine phylogenetic methods with morphological methods to explore the cryptic biodiversity of coccoid green algae.

Key words: coccoid green algae, phylogeny, Trebouxiophyceae, Chlorophyceae, biodiversity, taxonomy