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First record of Potamogetonaceae for the state of Rio Grande do Norte, Brazil.

Potamogetonaceae is a small subcosmopolitan monocot family of aquatic herbs with submersed or floating leaves, belonging to the order Alismatales (Haynes and Holm-Nielsen, 2003). It is a taxonomically complex family (Kaplan et al., 2013), which may comprise three or more genera, depending on the including of Zannichelliaceae (Haynes and HolmNielsen, 2003; APGIII 2009; Kaplan et al., 2013). Potamogeton is the largest genus of Potamogetonaceae, with ca. of 72 species (Kaplan et al., 2013), occurring mainly in temperate regions (Haynes and Holm-Nielsen, 2003). Some species of the genus are ecologically relevant as a source of food, shelter and reproduction site for several aquatic invertebrates and birds (Haynes, 1985). In Brazil, Bove (2014a) recorded 12 species in three genera of Potamogetonaceae: Potamogeton, Stuckenia Börner and Zannichellia P. Micheli ex L. In the country, these three genera are found together only in the extreme south state of the Rio Grande do Sul (Bove, 2014a). On the other hand, Potamogeton is the only genus of Potamogetonaceae occuring in the tropical Northeast region of Brazil, with six species (Bove, 2014a). Nevertheless, to our knowledge, none species of Potamogeton has been cited for the state of Rio Grande do Norte (Rodrigues and Irgang, 2001; Haynes and Holm-Nielsen, 2003; Bove, 2014a, 2014b). As a part of a survey of the aquatic plants in the ApodiMossoró river basin (Henry-Silva et al., 2010), this work provides the first record of the Potamogetonaceae for the Rio Grande do Norte state. Specimens were collected during expeditions in November 2013 to Santa Cruz reservoir, near the municipality of Apodi (05°48’43.59” S; 037°49’48.56” W). The specimens were deposited in the Herbarium of the Federal University of Roraima (code, UFRR). The identification of the specimens was based on Rodrigues and Irgang (2001) and Haynes and Holm-Nielsen (2003). Material examined: BRAZIL. Rio Grande do Norte: Apodi, 25/XI/2013, fr., Henry-Silva s.n. (UFRR 3932). Potamogeton pusillus can be easly recognized among Neotropical species with submersed leaves, free basal sheats and linear blades by the absence of keels in its fruits (Haynes and Holm-Nielsen, 2003). This species is early cosmopolitan and is represented in the Neotropics only by P. pusillus var. pusillus, where it extends from Mexico to Argentina (Haynes and Holm-Nielsen, 2003). It has been recorded for some states in all Brazilian regions, with the exception of the northern region (Bove, 2014a). In the Northeastern region, P. pusillus has been found in the states of Alagoas, Bahia, Ceará, Paraíba, Pernambuco (Bove, 2014a, b). The record of P. pusillus in the Santa Cruz reservoir extends the known geographic distribution of this species, emphasing the importance of surveying the biodiversity of macrophytes in the state, especially in areas of the Biome Caatinga, where other taxa have been recently recorded (Henry-Silva et al., 2013). In addition, this study adds Potamogetonaceae to the Rio Grande do Norte flora, what is particularly significant since to the state Forzza et al. (2010) have registered the lowest number of flowering plant species among the 27 states of Brazil.