Phytotaxa 201 (4): 241–255 www.mapress.com/phytotaxa/ Copyright © 2015 Magnolia Press Article PHYTOTAXA ISSN 1179-3155 (print edition) ISSN 1179-3163 (online edition) Accepted by Rafael Riosmena-Rodriguez: 14 Jan. 2015; published: 5 Mar. 2015 http://dx.doi.org/10.11646/phytotaxa.201.4.1 241 Taxonomic reassessment of Gracilaria cearensis (Rhodophyta, Gracilariales), a poorly defined yet common flattened species based on morphological and molecular analysis including topotype collections LUANDA PEREIRA SOARES 1,5* , CARLOS FREDERICO D. GURGEL 2,3,4 & MUTUE TOYOTA FUJII 5 1 Post-Graduate Program “Biodiversidade Vegetal e Meio Ambiente”, Instituto de Botânica, Av. Miguel Estéfano, 3687, São Paulo, SP, 04301-902, Brazil 2 Departamento de Botânica, Centro de Ciências Biológicas, Universidade Federal de Santa Catarina, Florianópolis, SC, 88040-970, Brazil 3 School of Earth and Environmental Sciences, The University of Adelaide, Aidelaide, SA 5005, Australia 4 State Herbarium of South Australia, DEWNR, South Australia Government, PO Box 2732, Kent Town, SA 5071, Australia 5 Instituto de Botânica, Núcleo de Pesquisa em Ficologia, São Paulo, SP, 04301-902, Brazil * Corresponding author: luanda87@gmail.com Abstract The genus Gracilaria is the major source of agarose in the world today and is one of the most species-rich genera in the Rhodophyta. Flat Gracilaria species are among the most taxonomically challenging taxa due to their widespread phenotypic plasticity among all species. Gracilaria cearensis is a flat species described in 1965 from Brazil. Its original description is not conducive to accurate taxonomic identifications and the delineation of this taxon remains elusive. New samples of G. cearensis were collected across a coastal length of 500 km including its type locality. Universal Plastid Amplicon (UPA) and the rbcL gene were used to confirm the phylogenetic and taxonomic status of this poorly known species. Results showed that this is a distinct species despite morphological similarities to G. hayi, G. cuneata, G. curtissiae, G. brasiliensis and G. galetensis. G. cearensis is sister to G. hayi yet the genetic divergence between these two species was 2% for rbcL and 1.08% for UPA, enough to consider them distinct taxa. However, newly generated molecular data placed G. smithsoniensis, an- other morphologically similar species, as conspecific with G. cearensis with only 0.07% rbcL sequence divergence between them. Key words: biodiversity, rbcL, taxonomy, UPA Introduction Gracilaria cearensis (A.B. Joly & F.C. Pinheiro 1965: 81) A.B. Joly & F.C. Pinheiro (1966: 131) is a tropical intertidal species with flat, strap-shaped branched thalli and commonly occurring in shallow reefs along the northeastern Brazilian coast (Pinheiro-Vieira & Ferreira 1968). In Brazil, G. cearensis has industrial potential as a source of agar and has attracted biotechnological interest due to its hemagglutination and antibiotic activity (Pinheiro-Vieira & Caland- Noronha 1971, Ainouz & Sampaio 1991). The species was originally described as Tylotus cearensis Joly & Pinheiro (1965: 81) based on material collected in Fortaleza, Ceará state, Brazil. The genus Tylotus J. Agardh (1876: 428) was excluded from the Gracilariaceae by Dawson (1949) based on the presence of zonate tetrasporangia in the type species, T. obtusatus (Sonder 1845: 56) J. Agardh (1876: 428). Later, Pinheiro & Joly (1966) transferred T. cearensis to Gracilaria Greville (1830: 121) in the light of its cruciately divided tetrasporangia. G. cearensis shows other main characters such as tubular nutritive cells present in both pericarp and the cystocarp floor, and spermatangial conceptacles described as “usually not confluent” as observed in most Gracilaria species. Since its description no further taxonomic or morphological studies have been performed in order to ascertain the status of this taxon, despite its purportedly widespread distribution in northeastern Brazil, from Ceará (Joly & Pinheiro 1965) to Bahia state (Nunes 2005). Morphologically, G. cearensis is similar to G. brasiliensis Gurgel & Yoneshigue-Valentin (2008: 255), G. cuneata Areschoug (1854: 351), G. galetensis Gurgel, Fredericq & J. Norris (2004: 181), G. hayi Gurgel, Fredericq & J. Norris