Phylogeny of Gonatozygon and Genicularia (Gonatozygaceae, Desmidiales) based on rbcL sequences

Gonatozygon and Genicularia have been placed in various families within the conjugating green algae, and recent treatments place them in the order Desmidiales, in a separate family Gonatozygaceae or within the family Peniaceae. Nucleotide sequences of the large subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase (rbcL) were determined for these genera and included in an analysis with published sequences for related genera in the families Zygnemataceae (filamentous conjugating green algae) and Mesotaeniaceae (saccoderm desmids), as well as charophycean and other outgroups. Gonatozygon and Genicularia form a strongly supported monophyletic group that is closely related to the saccoderm desmid, Roya. These three genera form a clade within a paraphyletic assemblage of genera from the Mesotaeniaceae and Zygnemataceae. The rbcL data suggest a close relationship of Roya with Gonatozygon and Genicularia, which is not supported by studies of cell wall ultrastructure but is congruent with some studies of pig...