XVI International Botanical Congess

Most investigators noting green pico-algae in plankton have provisionally designated them as AChlorella-like@ or ANannochloris-like@. The systematic position of these important primary producers need to be reconsidered. The limnic coccoid species which propagate by autosporulation should be classified within the genera Choricystis, Nanochlorum (Trebouxiophyceae), Mychonastes and Pseudodictyo-sphaerium (Chlorophyceae s.str.). Despite of morphological similarities, comparative 18S rRNA gene analyses reveal a polyphyletic relationship of these algae. The eucaryotic picoplankton of marine habitats is highly diverse and belong to different divisions of algae. The majority of chlorophycean taxa investigated until now by molecular phylogeny e.g. Bathycoccus, Pycnococcus, Ostreo-coccus are Prasinophyceae of coccoid morphology.