It includes prominent members of the global picoplankton community, which plays a central role in the oceanic carbon cycle.

The first member of the genus, O. tauri, was discovered in 1994 in an investigation of the picoplankton in the Thau lagoon by Courties and Chretiennot-Dinet using flow cytometry.

[2] O. tauri was immediately placed in the class Prasinophyceae based on the presence of characteristic chlorophyll pigments and Chlorophyceae-related carotenoids[1] as well as cell ultrastructure, and its position was later confirmed by analysis of its 18S rDNA.

[3] Molecular phylogenetic analysis based on the 18S rDNA sequence led the definition of a new class, the Mamiellophyceae, that contains Ostreococcus species and placed them within the Bathycoccaceae family.

[9] The draft metabolic networks of these two Ostreococcus species were reconstructed from the KEGG database, thermodynamically constrained, elementally balanced, and functionally evaluated in 2012.