This is distributed in east-central states with a curiously fragmented range from Appalachian to Ozark regions (K). One concentration of records occurs in s. Ind. and nc. Ky., perhaps centered on glacial refugia along the lower Kentucky River (as in Boechera dentata) and lower Salt River (as in Phlox pilosa). It has sometimes been confused with paniculata, but differs in several characters (Wherry 1929-34; F, Cr, W). It tends to flower earlier (mostly early Jun to mid-Jul versus late Jun to early Sep). Inflorescences are "copiously glandular" (F) at least on bracts (W), in contrast to "glabrous or pubescent" (F) in paniculata, with bracts "pubescent with non-glandular hairs" (W). However, corolla tubes are glabous versus usually pubescent. Anthers are included versus partly exserted. P. amplifolia tends to be shorter (45-100 cm versus 70-120 cm), and usually has more fewer nodes (7-15 versus 14-35). Leaves tend to have broader shape (l/w mostly 2-3 versus 3-4) and denser pubescence on both surfaces (scabrous-hirtellous versus largely glabrous). It tends to occur in more mesic woods on slopes, while paniculata usually occurs on floodplains. A few colls. suggest hybridization between these two species, but there is no definitive evidence.