Transferring Gracilaria irregularis (Gracilariaceae, Rhodophyta) from Thailand to Gracilariopsis based on morphological and molecular analyses Narongrit Muangmai, 1 Yukimasa Yamagishi, 2 Giuseppe C. Zuccarello, 1 Anong Chirapart 3 and Khanjanapaj Lewmanomont 3 * 1 School of Biological Sciences, Victoria University of Wellington, Wellington, New Zealand, 2 Department of Marine Biotechnology, Faculty of Life and Biotechnology, Fukuyama University, Hiroshima, Japan, and 3 Department of Fishery Biology, Faculty of Fisheries, Kasetsart University, Bangkok, Thailand SUMMARY Gracilaria irregularis, endemic to Thailand, was origi- nally described from Ao Len, Trat peninsula, Thailand, and was characterized by a short, succulent thallus with irregular branching, verrucosa-type spermatangia (a taxonomic criterion for Gracilaria) and the absence of nutritive filaments (a taxonomic criterion for Gracilariopsis). Due to the combination of characters diagnostic of both the genera Gracilaria and Graci- lariopsis, the taxonomic status of this species is unclear. This present study reassesses the identity of G. irregularis based on morphological features and the large subunit of ribulose-bisphosphate carboxylase/ oxygenase gene sequences. Newly collected samples from the type locality and KU collection were investi- gated. Our morphological re-examinations were rela- tively similar to the original type description, except that the male plants showed superficial chorda-type spermatangia, an important characteristic recognized in Gracilariopsis. Molecular analysis placed G. irregularis in the Gracilariopsis clade, forming a well-supported clade with Gracilariopsis bailiniae. Detailed morphology and molecular phylogenetic analyses clearly showed that G. irregularis is congruous with the generic concept of Gracilariopsis, and consequently the new combination of Gracilariopsis irregularis is proposed. We believe that in the original description a heterogeneous holotype was used. Our data also shows the problems that can occur when collections are made of multiple plants, of similar external morphology, to describe new species. Key words: Gracilariaceae, Gracilariopsis irregularis, Gracilariopsis, morphology, rbcL, red algae, spermatangia, Thailand. INTRODUCTION For more than a decade, the systematic of the marine red algal family Gracilariaceae has been extensively investigated and increasingly has relied on molecular data, together with detailed comparative morphology (e.g. Bellorin et al. 2002; Gurgel & Fredericq 2004; Kim et al. 2006; Muangmai et al. 2012). Morphologi- cally, identification of this family is based on internal anatomy of mature cystocarps and spermatangial arrangements (Fredericq & Hommersand 1990; Gurgel & Fredericq 2004). The Gracilariaceae presently contains seven distinct genera (Gurgel & Fredericq 2004), of which four genera, Congracilaria Yamamoto, Gracilaria (G.) Greville, Gracilariopsis (Gp.) E.Y. Dawson and Hydropuntia Montagne, are known in Thailand (Terada et al. 2004; Chirapart 2008). Among the four genera recognized in Thai waters, Gracilaria is the most diverse and widespread genus: nine species have been recorded so far, two of which, namely G. irregularis Abbott and G. minuta Lewmanomont are reported as endemic to Thailand (Abbott 1988; Lewmanomont 1994; Terada et al. 2004). Gracilaria irregularis I.A. Abbott was originally described based on collections from Ao Len, Trat Peninsula, Thailand, and it was characterized by inflated thalli with irregular branching, deep pot-shaped spermatangial conceptacles (verrucosa-type), and the absence of nutritive filaments (Abbott 1988). This species is known only from the Gulf of Thailand (Terada et al. 2004; Chirapart 2008) and commonly grows on sandy-mud bottom in the lower intertidal (0.5 m depth), attaching to shell and rock (Abbott 1988; Lewmanomont 1994). Due to little research on this species, detailed morphology, phylogenetic relation- ships and its ecology are poorly characterized. The taxonomic status of G. irregularis has long been in confusion, owing to the inconsistent views of *To whom correspondence should be addressed. Email: ffiskpl@ku.ac.th Communicating editor: S-M. Lin. Received 28 February 2013; accepted 18 June 2013. doi: 10.1111/pre.12032 Phycological Research 2014; 62: 29–35 © 2013 Japanese Society of Phycology