Study system
Paspalum vaginatum is distributed throughout tropical and subtropical saline ecosystems worldwide (Duncan & Carrow, 2000). It is characterized by two common ecotypes that differ in shoot and leaf morphology, referred to as the ‘coarse-textured’ and ‘fine-textured’ ecotypes (Fig. 1B; Duncan & Carrow, 2000). The fine-textured ecotype is more economically important because its prostrate growth form and smaller leaves makes it valuable for use as a turfgrass; the coarse-textured ecotype has also seen limited use as a dune stabilizer. Within the US, the coarse-textured ecotype is typically found on the Gulf Coast and Florida, while fine-textured plants are found on the Atlantic coast from North Carolina to Georgia (Duncan & Carrow, 2000). Due to the focus on collecting samples for turf breeding programs, the USDA P. vaginatum germplasm collection is composed almost entirely of fine-textured accessions (USDA-ARS, 2015).
Paspalum vaginatum and its closely related non-halophytic sister species P. distichum together comprise the Disticha clade, which is distantly related to the other ca. 300 species in the genus (Burson, 1981; Scataglini, Zuloaga, Giussani, Denham, & Morrone, 2014). The two species are morphologically very similar and often confused (Bor & Guest, 1968; Brummitt, 1983), although they are distinguishable based on cpDNA and nuclear sequences (Scataglini, Zuloaga, Giussani, Denham, & Morrone, 2014). Unlike P. vaginatum , P. distichum is believed to be predominantly hexaploid (2n = 60), with tetraploid (2n = 40), pentaploid (2n = 50) and hyperpentaploid (2n = 52, 54, 57, and 58) cytotypes occurring occasionally in the wild Echarte, Clausen, & Sala, 1992). A putative diploid P. distichum accession has also been reported (Eudy, Bahri, Harrison, Raymer, & Devos, 2017).