Prochlorophytes constitute a polyphyletic "pigment" group of Oxyphotobacteria, which are characterized by a diverse molecular structure and contrasting functional properties of the light-harvesting complex. The genes for Chl a/b apoproteins of prochlorophytes are homologous to the isaA gene of cyanobacteria and are not homologous to chloroplast Cab-polypeptides; i.e., the antennae of Oxyphotobacteria and plastids have a diverse evolutionary origin. An investigation of the prochlorophytes indicates multiple variants of light-harvesting complexes in the primitive form and their selective reduction in diverged lineages of Oxyphotobacteria. Evidence in favor of the global role of Prochlorococcus marinus in primary oceanic production is among the major achievements of biology at the end of the 20th century.