551 J. Phycol. 38, 551–563 (2002) PHYLOGENY AND SYSTEMATICS OF THE MARINE ALGAL FAMILY GRACILARIACEAE (GRACILARIALES, RHODOPHYTA) BASED ON SMALL SUBUNIT rDNA AND ITS SEQUENCES OF ATLANTIC AND PACIFIC SPECIES 1 Alexis M. Bellorin 2 Departamento de Biología, Universidad de Oriente, AP 245, Cumaná, Venezuela Mariana C. Oliveira and Eurico C. Oliveira Departamento de Botânica, Instituto de Biociências, Universidade de São Paulo, Caixa Postal 11461, CEP 05422-970, São Paulo, Brazil We sequenced the small subunit rDNA and inter- nal transcribed spacer region of Gracilariaceae from the tropical Atlantic and Pacific, with emphasis on flattened or compressed species. Sequence compari- sons confirmed three main lineages of Gracilariaceae: Curdiea/Melanthalia, Gracilariopsis /Gracilariophila, and Gracilaria. The Curdiea/Melanthalia diverged early in the family. Gracilariopsis was paraphyletic, because at least one Gracilariophila species evolved from it. The At- lantic Gracilariopsis were monophyletic and separated from the Pacific lineages. The Gracilaria included all species referable to its own species and to Hydropuntia, which was paraphyletic, formed by distantly related lin- eages. The new combination Gracilaria pauciramosa (N. Rodríguez Ríos) Bellorin, M. C. Oliveira et E. C. Oliveira is proposed for Polycavernosa pauciramosa N. Rodríguez Ríos. Recognition of subgenera within Gracilaria, based on spermatangial arrangement, was not supported. Instead, infrageneric groups were de- lineated by geographic origins and combinations of reproductive characters. Most Pacific species with ei- ther “textorii” or “verrucosa” type spermatangia were deeply separated from Atlantic species. Within the Atlantic Gracilaria, a lineage encompassing mostly tropical cylindrical species with “henriquesiana” type spermatangia and distinctive cystocarp anatomy was recognized. A lineage was also retrieved for cold wa- ter stringy species with verrucosa type spermatangia. Several species from the western Atlantic are closely related to Gracilaria tikvahiae McLachlan with nearly identical morphology. On the other hand, most flat- tened species from the tropical Atlantic were closely related despite their diverse morphologies. The in- terpretation of our data in addition to the literature indicates that more populations from the Indo-Pacific must be studied before a general picture of Gracilar- iaceae evolution can be framed. Key index words: agarans; agarophytes; Gracilaria; Gracilariaceae; Gracilariopsis; Hydropuntia; ITS; phy- logeny; SSU rDNA Abbreviations: G., Gracilaria; Gl., Gracilariophila; Gp., Gracilariopsis; GTR, general time reversible; ITS, internal transcribed spacer; ML, maximum like- lihood; MP, maximum parsimony; NJ, neighbor join- ing; SSU, small subunit The gracilarioid algae include some of the most valuable marine plants. They have been intensively in- vestigated in the last 30 years and comprehensive in- formation about biology (Oliveira and Plastino 1994), cultivation (Oliveira et al. 2000), and utilization (cf. Critchley and Ohno 1998) has been published. How- ever, there is still much to be done to resolve the many remaining taxonomic problems (e.g. Bird 1995). Dif- ferent approaches have been attempted to clarify the taxonomy of gracilarioid algae (sensu Oliveira et al. 2000), primarily the genera Gracilaria Greville (1830), Gracilariopsis E. Y. Dawson (1949), and the disputable genus Hydropuntia Montagne (1842; valid name for Polycavernosa C. F. Chang et B. M. Xia 1963, see Wynne 1989). Reproductive anatomy (e.g. Dawson 1949, Yama- moto 1978, Gargiulo et al. 1992), chemistry (Bird et al. 1987), crossability, and karyology (McLachlan et al. 1977, Bird et al. 1982, 1986, 1990a, Guiry and Fream- hainn 1985, Plastino and Oliveira 1988, 1997, Yamamoto and Sasaki 1988, Godin et al. 1993, Kapraun 1993) and modern techniques, including DNA fingerprinting (Goff and Coleman 1988, Rice and Bird 1990, Wattier et al. 1997) and gene sequencing (Bird et al. 1990b, 1992, 1994, Destombe and Douglas 1991, Goff et al. 1994), have been the keystone aspects investigated. It has been concluded that species delimitation is reliable only when based on a combination of characters, pre- ferably experimental data, because anatomical features may be equivocal and cryptic species have been re- ported (Bird and Rice 1990, Bird et al. 1994, Steentoft et al. 1995). Unfortunately, nonmorphological infor- mation is almost entirely restricted to the terete and economically valuable taxa, especially those from tem- perate waters. The large assemblage of compressed and flattened forms from tropical waters, which con- stitute most of the described gracilarioid algae, has been largely neglected. Among the experimental tools for discriminating taxa within this group, the comparison of homologous gene sequences has several advantages over other ap- 1 Received 14 August 2001. Accepted 19 February 2002. 2 Author for correspondence and present address: Departamento de Botânica, Instituto de Biociências, Universidade de São Paulo, Caixa Postal 11461, CEP 05422-970, São Paulo, Brazil. E-mail almiguel@ yahoo.com.