Although descriibed in 1891 and well treated by Hitchcock & Chase (1950), this widespread southeastern taxon has been somewhat overlooked in recent literature. Recognition as a species was advanced by Mohlenbrock (1985), but it was treated as a subspecies in FNA 25. D. joorii is widely scattered within the central Mississippi and lower Ohio Valleys, and may extend south to Mexico (FNA 25; Hill 2007c, Ladd & Thomas 2015); Thomas (2017) indicated that the type of joorii (US) has been misinterpreted, but that coll. does appear to be the same taxon outlined here. D. joorii has also been reported from Atlantic States, from Flo. to Va. (Hitchcock & Chase 1950), but it has been generally included within commutatum in recent treatments of that region (W; Majure et al. 2023). D. joorii of western Ky. typically occurs in subhydric to submesic woods, especially on riparian levees, mossy banks and hummocks along medium to small-sized streams. Further collection is needed to document its range and improve description. Although joorii is close to commutatum, complete colls. can be reliably distinguished. D. joorii differs in its more elongated spikelets (up to 2.9-3.2 mm versus 2.6-2.9 mm), with more pointed lemmas; panicles tend to be smaller (mostly 3-9 cm long versus 6-12 cm); blades are falcate (versus almost symmetric at base); culms are usually shorter (mostly 20-40 cm versus 40-70 cm), and decumbent to sprawling from loose caudices or rhizomes (versus erect and cespitose).