Phytotaxa 326 (2): 115–128 http://www.mapress.com/j/pt/ Copyright © 2017 Magnolia Press Article PHYTOTAXA ISSN 1179-3155 (print edition) ISSN 1179-3163 (online edition) Accepted by Jeffery Hughey: 11 Oct. 2017; published: 24 Oct. 2017 https://doi.org/10.11646/phytotaxa.326.2.3 115 Sporolithon indopacificum sp. nov. (Sporolithales, Rhodophyta) from tropical western Indian and western Pacific oceans: First report, confirmed by DNA sequence data, of a widely distributed species of Sporolithon G.W. MANEVELDT 1* , P.W. GABRIELSON 2 & J. KANGWE 3 1 Department of Biodiversity & Conservation Biology, University of the Western Cape, P. Bag X17, Bellville 7535, South Africa. 2 Biology Department and Herbarium, Coker Hall CB 3280, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, 27599-3280, USA. 3 Tanzania Fisheries Research institute (TAFIRI), P. O Box 78850, Dar es Salaam, Tanzania * gmaneveldt@uwc.ac.za Abstract Sporolithon indopacificum sp. nov. is characterized from Zanzibar Island, Tanzania. rbcL and psbA markers indicate that the species is unique compared to all other Sporolithon species that have thus far been sequenced. The species previously had been collected at Nukulau, Suva, Fiji and identified as S. episporum. The two species bear a close morpho-anatomical resemblance differing only by degree in three measured tetra/bisporangial characters. This is the first Sporolithon species confirmed to be widely distributed in the Indo-West Pacific based on DNA sequences. Key words: biogeography; coralline algae; morpho-anatomy Introduction Non-geniculate coralline red algae (Corallinophycidae, Rhodophyta) are widespread and noticeable shallow-water benthic components in all the world’s oceans. They are essential structural components of coral reefs (e.g. Taylor 1950, Littler & Doty 1975, Adey et al. 1982) and rhodolith beds (e.g. Amado-Filho et al. 2007, 2010, Villas Bôas et al. 2015, Brasileiro et al. 2016, Riosmena-Rodríguez et al. 2017). Rhodolith beds are themselves widely distributed, but are best represented along the tropical western Atlantic (Foster 2001, Riosmena-Rodríguez et al. 2017) where species ascribed to Sporolithon Heydrich (Sporolithales) have been recognized as major contributors (e.g. Bahia et al. 2011, 2014a, 2014b, 2015, Riosmena-Rodríguez et al. 2017). In the Indian and western Pacific oceans, 11 Sporolithon species names have been applied to rhodoliths based on morpho-anatomical characters (Guiry & Guiry 2017). The most widely reported species include S. durum (Foslie) R.A.Townsend & Woelkerling (e.g., Townsend et al. 1995, Nelson et al. 2014), S. episoredion (W.H.Adey, R.A.Townsend & Boykins) Verheij (e.g., Verheij 1992, 1993), S. episporum (M.Howe) E.Y.Dawson (e.g., Keats & Chamberlain 1993, Oliveira et al. 2005), S. molle (Heydrich) Heydrich (e.g. Verheij 1993) and S. ptychoides Heydrich (e.g., Keats & Chamberlain 1993, Oliveira et al. 2005). To date, none of the distributions of these widely reported species have been confirmed by DNA sequence data; where names of Sporolithon species have been applied to sequenced specimens, other than type or topotype material, those names have been applied incorrectly (Richards et al. 2017). In a recent investigation quantifying the percent cover of coralline algae and other major benthic organisms that form the rhodolith beds in Chwaka Bay, Zanzibar, Tanzania, a species of non-geniculate coralline algae, attributed to Sporolithon, was collected. Initial morphological and anatomical investigations suggested that the specimens belonged to S. episporum reported for the region (Oliveira et al. 2005), but DNA sequences showed that it was new to science. Interestingly, an rbcL sequence of another specimen in our collection from Nukulau, Suva, Fiji perfectly matched the sequence obtained from the Tanzanian specimens, providing further insight into the ongoing debate on the generally widely reported distributions of coralline algae. Here we provide a full taxonomic account, based on both morpho- anatomy and DNA sequence data, of the new species and discuss non-geniculate coralline distribution patterns.