DISTINGUISHING MULTIPLE LINEAGES OF PEDIASTRUM DUPLEX WITH MORPHOMETRICS AND A PROPOSAL FOR LACUNASTRUM GEN. NOV(1).

Accurately defining species boundaries in the green algae (Chlorophyta) is integral for studies of biodiversity and conservation, water-quality assessments, and the use of particular species as paleoindicators. Recent molecular phylogenetic and SEM analyses of the family Hydrodictyaceae (Chlorophyta) resolved three phylogenetic lineages of isolates with the Pediastrum duplex Meyen 1829 phenotype. The present study employed analyses of cell shape and cell wall ultrastructure to determine if the three lineages possessing the P. duplex morphotype were distinguishable. Only one of the groups, containing isolates with the P. duplex var. gracillimum West et G. S. West phenotype, was shown to be morphologically distinct from the other two P. duplex groups. The erection of a new genus, Lacunastrum, is proposed to recognize this group as a separate taxon.