The genus Paspalum L. is an important member of the Paniceae tribe (Poaceae) and includes between 330 and 400 species, most of which are native to the tropical and subtropical regions of the Americas [1–3]. Paspalum species can be found in diverse habitats, such as subtropical rainforests, savannas, marshes and dunes, but they are more frequently found in the natural grasslands of eastern Bolivia, Paraguay, central and southern Brazil, northern Argentina and Uruguay . The main center of origin and diversity of the genus is considered to be located in the South American tropics and subtropics , primarily in central Brazil, where numerous species appear to be associated with savannas and rocky terrain. Brazil harbors the greatest number of Paspalum species [4, 5], with approximately 220 species that exist in nearly all herbaceous plant communities within different ecosystems .
Because of this degree of complexity, the division of the Paspalum genus into subgenera, sections or informal groups has been proposed by many authors and has been extensively discussed [1–3, 7–16]. Currently, four subgenera are recognized within Paspalum: Paspalum subg. Anachyris Chase, P. subg. Ceresia (Pers.) Rchb., P. subg. Harpostachys (Trin.) S. Denham and P. subg. Paspalum, the last of which consists of approximately 265 species divided into 25 informal groups [1, 14]. However, such rankings have been based on morphological similarities, and the evolutionary and genetic relationships between these groups are not always clear. Several species, mainly within Paspalum subg. Paspalum, are of economic importance for foraging, turf and ornamental purposes  in different parts of the world. Dallisgrass (Paspalum dilatatum Poir., Dilatata group) and bahiagrass (P. notatum Flüggé, Notata group) are especially important and are widely used for forage, mainly in the southern United States of America (USA) [18, 19]. P. atratum Swallen (Plicatula group) has been the object of growing interest for use as forage in areas that are subjected to periodic flooding in Florida (USA), northeastern Argentina, Brazil, Thailand, the Philippines and Australia . In addition, Paspalum scrobiculatum L. (‘Kodo millet’, Plicatula group) is cultivated in India as a cereal crop [3, 20], and Paspalum vaginatum Sw. (Disticha group)  and P. notatum are widely grown as turf grass.
Because of the widespread interest in several species of this genus, many accessions have been conserved in germplasm banks and distributed throughout various countries for cultivar development and cytogenetic studies. However, the use of some accessions is restricted due to difficulty with accurate taxonomical identification. In Brazil, despite constant evaluations of germplasm banks and taxonomic reviews , many species of Paspalum, especially those included in the Plicatula Group, remain unidentified. This deficit presents a problem because the correct identification of germplasms and the quantification of their variability are necessary for the development of conservation and breeding programs.
The complexity of the taxonomical classification of Paspalum germplasms results from the complex evolutionary history of the group. Polyploidy occurs at a high frequency within the genus [23, 24] and has played a crucial role in the evolution of Paspalum. Most species have × = 10 as the basic chromosome number, with ploidy levels that range from diploid to hexadecaploid . Diploid species are not rare within the genus [3, 25–32], but nearly 80% of the investigated species are polyploids, among which 50% are tetraploid, and most of these tetraploids are apomictic [24, 33]. Many Paspalum species comprise sexual diploid and apomictic polyploid cytotypes, and several have been shown to have arisen through natural hybridization . However, interspecific hybridization and allopolyploidy are not always morphologically evident in Paspalum species; therefore, additional methods of taxonomic classification are required .
Many taxonomical and species characterization problems arise as a consequence of the great morphological variation present in agamic complexes. P. notatum is a good example of this situation, because it forms an agamic complex and presents wide morphological variation [7, 36, 37]. This species is a perennial rhizomatous turf and forage grass and is recognized as a major constituent of the native grasslands of the New World, being found from Central Eastern Mexico to Argentina and throughout the West Indies . This grass is economically important and is widely used for forage production, mainly in the southern USA .
Various morphological and cytological forms are recognized within P. notatum[7, 37]. This species includes several genotypes, which differ in both their ploidy levels and their reproductive systems. The diploid cytotype (2n = 2× = 20) is sexual and self-incompatible [38, 39], whereas the tetraploid cytotype (2n = 4× = 40) is a self-compatible pseudogamous aposporous apomict . Apomixis in tetraploid P. notatum can be either obligate or facultative . In botanical terms, the tetraploid cytotypes are usually considered to be the typical form of P. notatum; as such, they form the variety notatum. On the other hand, the diploid cytotypes are classified as belonging to the saurae variety based on their distinct morphological characteristics . In addition to these two widely recognized varieties, Döll  proposed the variety latiflorum, which was accepted by some taxonomists [36, 42, 43] until the mid-1980s. However, P. notatum var. latiflorum is not currently recognized.
Molecular makers are of great value in plant studies and have been used for multiple purposes, including estimating the genetic diversity, determining accession relationships, elucidating evolutionary relationships, aiding in the taxonomic classification of many plants [44–49] and aiding in the identification of botanical varieties [50, 51]. In addition, utilizing molecular markers that regularly identify many genetic polymorphisms at low taxonomic levels makes it possible to address the relationship between morphological and genotypic variation.
The molecular markers that are more informative for the discrimination of closely related genotypes include microsatellite sequence markers [52–54]. Microsatellites are tandem repeat sequences of 1 to 6 nucleotides that are widely distributed in the genome . However, these markers are usually species specific, and in the Paspalum genus, few microsatellite markers are available for P. vaginatum, P. dilatatum and the related species , P. notatum and P. atratum. However, primers designed for source species have been successfully employed to amplify nuclear SSRs in closely related taxa when the DNA regions that flank the microsatellite loci are sufficiently conserved [57, 59–67].
The main objectives of this study are (1) to evaluate the informative potential of SSRs for genetic discrimination in different species of Paspalum using markers developed for P. atratum and P. notatum; (2) to conduct an in-depth study of the extent, distribution and structure of the genetic variation of P. notatum in a South American collection of this species; and (3) to evaluate the genetic patterns and relationships among different morphological types found in this species and correlate them with their geographic distribution.