Characterization and phylogenetic affinities of the red alga Chondrophycus flagelliferus (Rhodomelaceae, Ceramiales) from Brazil on the basis of morphological and molecular evidence

Abstract

A detailed study of the vegetative and reproductive morphology of Chondrophycus flagelliferus from Brazil is provided. The species possesses axial segments, each bearing two periaxial cells, a situation characteristic for the genus Chondrophycus. Within Chondrophycus, C. flagelliferus belongs to the subgenus Palisadi, section Palisadi, on the basis of the presence of a palisade-like outer cortical cell layer as seen in transverse sections of branchlets; the absence of secondary pit connections between cortical cells; the fertile periaxial cell with two pre-sporangial cover cells, the tetrasporangium initial and the post-sporangial cover cell that will develop into the corticating system; and the right-angled tetrasporangial arrangement. The phylogenetic position of this species within Laurencia sensu lato is inferred from parsimony and Bayesian analyses of chloroplast-encoded rbcL sequences from 39 Rhodomelaceae using two Ceramiaceae as the out-group. This study corroborates the taxonomic decision to split Laurencia sensu lato in the genera Laurencia, Chondrophycus and Osmundea, and indicates that rbcL provides sufficient phylogenetic signal to infer species-level relationships within the Laurencia sensu lato complex. Synapomorphic morphological characters uniting Laurencia and Chondrophycus include the same origin of the spermatangial filaments and tetrasporangia. The principal character separating both genera is the number of periaxial cells per vegetative axial segment. We hypothesize that the ancestor of the Laurencia sensu lato complex most likely possessed two periaxial cells per axial segment. The molecular data indicate that C. flagelliferus is closely related to the C. papillosus complex, and that, as originally described, C. translucidus belongs in the genus Laurencia.