Phylogenetic relationships of Dichotomaria (Nemaliales, Rhodophyta) with the proposal of Dichotomaria intermedia (R.C.Y. Chou) comb. nov.

Abstract

Abstract Species delineation in the calcified red algal genus Dichotomaria is difficult due to the high degree of morphological similarity observed in these algae; thus, species descriptions are based on a limited set of morphological characters. In this study, we conducted phylogenetic analyses of plastid rbcL and mitochondrial cox1 sequences and detailed morphological observations on 28 specimens of Dichotomaria from the Indo-Pacific, Bermuda, the Galápagos Islands, and the Lesser Antilles. As a consequence, we propose the new combination Dichotomaria intermedia (R.C.Y. Chou) comb. nov. based on Galaxaura intermedia. This species has flattened branches, three to four cortical cell layers, four sterile branches issuing from the hypogynous cell, and a pericarp formed from the basal cell, as in the genus Dichotomaria. In the rbcL tree, D. intermedia formed a group with Dichotomaria tenera from South Africa. Our results confirmed the occurrence of 11 species and one variety: Dichotomaria apiculata, Dichotomaria australis, Dichotomaria diesingiana, Dichotomaria falcata, Dichotomaria hommersandii, Dichotomaria intermedia, Dichotomaria marginata, Dichotomaria obtusata, D. obtusata var. major, Dichotomaria papillata, Dichotomaria spathulata, and D. tenera. Further study is required to address unidentified genetic groups that cannot currently be assigned to known species groups.