 Studies on the eyespot apparatus of green algae eventually led to the identification of the photoreceptor channelrhodopsin and the emergence of the research area optogenetics.Melkonian also studied the systematics, diversity and evolution of algae with emphasis on green algae, cryptophytes, and euglenophytes but also heterotrophic protists, such as the Picozoa.Molecular phylogenetic analyses helped to identify the flagellate Mesostigma as the earliest divergence in the Streptophyta and the Zygnematophyceae as the likely sister group to the embryophyte land plants.