Absolute Configuration Analysis of the Flagellar Apparatus in Cladophora and Chaetomorpha Motile Cells, With an Assessment of the Phylogenetic Position of the Cladophoraceae (Ulvophyceae, Chlorophyta)

Absolute configurational analyses of flagellar apparatus components were performed on the motile cells produced by three species of Cladophora, Cl. dalmatica Kütz., Cl. flexuosa (Dillw.) Harv., and Cl. glomerata (L.) Kütz., and by Chaetomorpha aerea (Dillw.) Kütz. There was little variation among the species. All of the flagellar apparatuses demonstrated the ulvophyceous features of 180° rotational symmetry, counterclockwise absolute orientation, and basal body overlap, as well as the alignment of the basal bodies perpendicular to the long axis of the cell. Diagnostic features included the nearly complete absence of C tubules from the basal bodies and the presence of a coarsely striated component dorsal to the two‐membered rootlets in all cells, as well as, in quadriflagellate cells, a tetralobate distal fiber, the coaxial arrangement of the lowermost pair of basal bodies, and the presence of a characteristic array of basal‐body‐associated striated bands. The distal fiber architecture, the presence of a “wing” in the X‐membered rootlets, and the “flattening” of the flagellar apparatus components suggests a close relationship of the Cladophoraceae to the Dasycladales, and indicates that these two groups may have shared a common ancestor, possibly ancient in terms of the geological time scale but relatively recent in the context of ulvophyceous evolution. A sizeable phylogenetic gap exists between the Cladophoraceae and uninucleate‐celled, presumably primitive members of the Ulvophyceae.