Branched Halymenia species (Halymeniaceae, Rhodophyta) in the Indo-Pacific region, including descriptions of Halymenia hawaiiana sp. nov. and H. tondoana sp. nov.

Abstract

Several species in the red algal genus Halymenia from the Indo-Pacific have been described with branched thalli, toothed margins, spinose proliferations on the blade, and a firm gelatinous texture. Previous works have synonymized many of these morphologically similar species with H. durvillei. Our increased taxon sampling and molecular data indicate that the taxonomy of the Indo-Pacific Halymenia species is in need of revision, and that several aspects of taxonomies proposed by previous authors now seem unlikely. Thus, the aim of the present work was to analyse species delimitation in branched Halymenia species. Molecular and morphological data for specimens from the coral triangle and peripheral Indo-Pacific localities (East African coast, Hawaii) were used to understand species delimitation for selected branched Halymenia spp. Phylogenetic analyses based on 29 rbcL gene sequences grouped the specimens in four well-supported clusters at the species level with high p-distances (2.7–5.3%). After the morphological analysis, five features were retained as diagnostic to identify the four species studied. Our analyses led to the recognition and description of two new species, H. hawaiiana from the Hawaiian Islands (previously erroneously called H. formosa) and H. tondoana from the Philippines. In addition, H. harveyana (currently treated as a subspecies of H. floresii in Australia) is reassessed and recognized at the species level. Specimens with seven orders of branching and a thick cortex (70–150 µm) formed a monophyletic group, including sequences from previous work, with mostly well-supported branches and with high p-distances at the species level. We propose to call this group the H. durvillei complex until further reassessment is completed. None of the sequences studied here grouped with H. floresii from the Mediterranean, suggesting that previous Indo-Pacific reports of the species were erroneous.