This is part of the setaceum complex, for which mapping here remains somewhat tentative. Only diploids (2n = 20) are known in this widespread southeastern complex, and the segregates are sometimes hard to distinguish (FNA 25). Both longepedunculatum and typical setaceum have ranges concentrated on the Coastal Plain, but perhaps extending up the Atlantic side to Va. and Md. (SERNEC 2023), and in the interior to Tenn., Ky. and Ohio (FNA 25).. Ky. records of both taxa are mostly from dry sandy soils in southeastern counties. The coll. mapped here from JEFF (MM for WKY) may represent a waif, since it was found near railroad tracks. Some authors (Banks 1966, W) have tended to exclude interior states from the range of this taxon; Banks considered that plants resembling var. longepedunculatum from Tenn., Ky., W.Va, Va. and N.J. were just atypical var. ciliatifolium. However, some of these plants do fall within the generally accepted circumscription of var. longepedunculatum, including Kearney's coll. from HARL (US) that became described as P. kentuckiense Nash. P. longepedunculatum has been treated as a variety or subspecies within P. setaceum (FNA 25), but it is more distinct than most other taxa included in the species. It has relatively small spikelets (1.4-1.8 x 0.9-1.3 mm versus 1.7-2.6 x 1.2-2.1 mm), and leaves that are mostly basal (versus cauline), usually more recurved, usually narrower (3-10 mm versus 3-18 mm), and usually glabrous except for ciliate margins (versus pubescent to glabrous). Typical setaceum also has relatively small spikelets (1.4-1.9 x 0.9-1.6 mm), compared to most other taxa in this complex.