Eukaryotic algae with chlorophyll b colonized land and evolved into embryophytes, today’s vegetation. Plant scientists have always been interested in the evolutionary origin of the land plant flora, but only in the 20th century was significant progress achieved through two “Green Revolutions”. In the first (starting in the 1970s), here termed the “Ultrastructural Revolution”, an in depth comparative analysis of the cytoskeletal systems of green algae led to the recognition of a group of green algae (now termed streptophyte algae) from which embryophytes likely evolved (other groups of green algae such as prasinophytes, ulvophytes, trebouxiophytes were also recognized during this period). Although initially greeted with skepticism, these results were splendidly corroborated during the second “Green Revolution”, here for convenience termed the “rRNA Revolution” (starting around 1990). While the second “Revolution” was under way, it came as a surprise that most green algal taxa ranging from order to genus were apparently para- or polyphyletic demonstrating the inadequacy of the previously used morphological traits to delineate these taxa requiring a complete overhaul of green algal systematics.

Since our laboratory had already been involved in the first two “Green Revolutions”, the third “Green Revolution” was initiated (around 1998). Our approach has been (1) to increase taxon sampling involving many novel isolations from nature, (2) to increase the data set (using the almost complete rDNA operon from both nucleus and plastid as well as other genes), (3) to employ both morphological and molecular characters to circumscribe taxa (today known as the “polyphasic” approach;*179, *186). The use of molecular characters for systematics/taxonomy has been greatly facilitated by the introduction of the concept of “nonhomoplasious molecular synapomorphies” (NHS;*187).

During the past five years, our laboratory has generated complete rDNA operon sequences from several hundred strains, not only of Viridiplantae, but also other algal groups such as Euglenozoa, dinoflagellates, and cyanobacteria. The results have led to novel insights into algal evolution and generated taxonomic revisions based on phylogenetic principles.

Contact: Birger Marin

*Numbers refer to the list of publications of Michael Melkonian