This is closely related to pusilla, but concentrated in Ala., Miss., La. and Ark. It extends north to se. Mo. and nw. Tenn. in counties adjacent to Ky. (K). Brock (2020) has recently reported micrantha from the vicinity of Zion Cemetery Road, where it is locally abundant in dry sandy mowed areas (BARR at APSC). H. micrantha differs from pusilla in several overlapping characters (W): calyx lobes slightly shorter than to slightly longer than corolla tube (versus 1/5 as long to slightly longer); corollas white (versus usually purple or violet), 2.0-5.5 mm long (versus 3.5-12.5 mm), the tube 0.8-2.5 mm long (versus 2-5.5 mm). It is more concentrated on relatively sandy (or granitic) soils. A more distinct southwestern relative is H. rosea (Raf.) Terrell, a diminutive plant with white to pink flowers (and 2n = 14), which is also known from se. Mo., close to Ky. but not Tenn. (Terrell 1996).