Phylogeny and taxonomy of Planktosphaeria, Follicularia and Herndonia gen. nov. (Sphaeropleales, Chlorophyceae) based on ultrastructure and 18S rDNA analyses

Abstract

ABSTRACT The two genera Planktosphaeria (the type Pl. gelatinosa G.M.Smith) and Follicularia (the type F. paradoxalis Miller) have numerous chloroplast segments, each with a single pyrenoid. Autospore reproduction was described only in Planktosphaeria; whereas naked, biflagellate zoospores were known in Follicularia. The generic circumscription of Planktosphaeria was once changed to zoospore-producing forms based on P. gelatinosa sensu Starr UTEX 124, but some authors did not accept the amendment. Recent molecular analyses showed that Pl. botryoides and Pl. texensis belonged to a clade separate from Pl. gelatinosa sensu Starr, and then, the two former species were dealt with as members of Follicularia; whereas the latter was retained in Planktosphaeria. However, the ground for assigning these species to the two genera was not ascertained. To resolve the taxonomic confusions, 18S rDNA phylogenetic relationships, and morphological and ultrastructural features of selected species of these genera and closely related taxa were examined. It is concluded that identification of UTEX 124 as P. gelatinosa and the amendment of the generic circumscription of Planktosphaeria were not acceptable. By comparing the original line drawings of F. paradoxalis with morphological and ultrastructural features of other zoosporic species of Planktosphaeria, the former was inferred to belong to a clade including both Pl. gelatinosa sensu Starr UTEX124 and Pl. maxima (Sz-group), all of which were assigned to Follicularia. For Pl. botryoides and Pl. texensis (Rz-group), Herndonia gen. nov. was proposed, that was also characterised ultrastructurally. The taxonomic states of Pl. gelatinosa and other autosporic members of Schizochlamydaceae and Radiococcaceae are discussed.