Mapping here is provisional. Several of these scattered records are tentative, pending further analysis of the longifolia complex, which includes diploids and tetraploids (Glennon & Church 2015). Some colls. may be transitional to, or confused with, tenuifolia, canadensis, lanceolata or purpurea; see notes under those species. The treatment of W is followed here, but further work is needed; the 2020 maps of W still appear to confuse Ky. data for longifolia with tenuifolia. Terrell (1996) indicated that these largely central Appalachian plants of H. longifolia could be named var. compacta (?= H. geniculata Raf. 1836, 4:102), but he ultimately combined them with var. longifolia. They tend to have "stems densely puberulent, especially near base, internodes (4-) 6-12 (-13), usually 15-40 mm long; inflorescences especially of northern and central Appalachian populations indeterminate and continuing to produce flowers into the autumn." Typical longifolia, in its strictest sense, is a more northern taxa of "dry sandy or rocky habitats [in] New England and maritime Canada, west to MN and SK, south to n. NJ, PA, n. IN, n. IL." (W). It is distinguished from var. compacta as follows (W): internodes 4-7 (versus 6-13); stipules of median nodes ovate, up to 3.3 x 3.5 mm (versus lanceolate or deltoid, up tp 3 x 2.5 mm), the apex often rounded (versus usually acute to acuminate). [Stipules in Houstonia are interpetiolar and fused to the connate leaf bases, but often shredding before end of summer.]