Mapping (and treatment) is provisional. This species may belong in an expanded Ensifolia clade (Majure et al. 2023); see notes under tenue. D. longiligulatum occurs from the prairie peninsular (centered on Ill.) and southeastern states to South America (FNA 25; Thomas 2015). In Tenn., there are many verified records from west to east (SERNEC 2023). In se Mo. it is "usually found along the draw-down zone of ephemeral wetlands and pond margins" on acid soils (Ladd & Thomas 2015; Thomas 2017). Together with close relatives leucothrix and meridionale, longiligulatum differs from the acuminatum complex (including lindheimeri) as follows. Spikelets are generally smaller (1.1-1.6 mm long versus 1.5-2.9 mm). Longer hairs form the true frontal ligule (mostly 1.7-4 mm versus 0.3-1.7 mm). Leaves are relatively small (mostly 2-7 cm x 2-6 mm versus 3-11 cm x 3-12 mm). And plants generally have some short pubescence (0.1-0.2 mm), although restricted to lower blade surfaces in longiligulatum; longer hairs are often lacking on leaves. However, longiligulatum may appear to intergrade with lindheimeri and spretum; see notes under those names. The close southern relative, D. leucothrix (Nash) Freckmann, is also typical of wet pinelands on the southeastern Coastal Plain, with no verified records from Ky. But it has been mapped across most southeastern and Atlantic regions by some authors (K), apparently including longiligulatum and some meridionale (see notes under that species). Compared to longiligulatum, leucothrix is more uniformly puberulent on stems and leaves (versus only lower blade surfaces), but there is little other obvious difference and Majure et al. (2023) have treated longiligulatum as a subspecies.