Reinstatement of Indian Ocean Porolithon coarctatum and P. gardineri based on sequencing type specimens, and P. epiphyticum sp. nov. (Corallinales, Rhodophyta), with comments on subfamilies Hydrolithoideae and Metagoniolithoideae

Abstract

Abstract Partial rbcL sequences were obtained from the type specimens of Lithophyllum coarctatum and L. gardineri. Both species were variably assigned to either Hydrolithon or Porolithon during the last two centuries, with L. coarctatum, from the tropical eastern Indian Ocean currently considered a synonym of L. gardineri from the tropical western Indian Ocean. Phylogenetic analyses show that both belong in Porolithon and that they are distinct species despite their morpho-anatomical similarities, including a columnar morphology. Porolithon epiphyticum sp. nov., from the same locality as P. coarctatum, Cocos-Keeling Islands, is the first reported epiphytic species in the genus. Eight of the currently recognized 15 species of Porolithon have had their type specimens sequenced to correctly apply names, including the generitype specimen. DNA sequencing provides independent confirmation that the morpho-anatomical character of the presence of horizontal fields of trichocytes without intervening vegetative cells is diagnostic for Porolithon. The generitypes of the four genera classified in the subfamily Metagoniolithoideae, Dawsoniolithon, Floiophycus, Harveylithon, and Metagoniolithon as well as Hydrolithon in the subfamily Hydrolithoideae, have not been sequenced. The taxonomic and nomenclatural uncertainties in each of these genera are discussed.