This is a rather poorly understood species of the central Mississippi Valley (W). In w. Ky. It is mostly known from relatively species-rich old fields and meadows that may have had open woods or "barrens" before settlement, often on fragipan soils of high terraces and upland swales. H. lobocarpum has been confused with typical H. densiflorum Pursh and H. interior Small, so that ranges of these three taxa remain somewhat uncertain (FNA 6, W). They all differ from prolificum in their generally larger inflorescences (with usually 7-17 flowers versus 3-7), smaller flowers (with petals mostly 5-10 mm versus 7-15 mm and stamens mostly 100-150 versus 150-500), smaller capsules (usually 4.5-6 mm long versus 7-14 mm), and narrower leaves (larger ones usually 1-7(12) mm wide versus 7-14 mm and perhaps relatively obtuse). However, there may be some intergradation; some plants named lobocarpum in Mo. May result from hybridization with prolificum (Y, Thomas 2017). Compared to densiflorum and prolificum, lobocarpum has generally intermediate-sized flowers and leaves (3-12 mm wide), but it is distinct from both species in its 4-5 styles and locules (versus usually 3), as evident in its lobed capsules. Typical densiflorum has moderately narrow leaves (ca. 3-8 mm) and occurs mostly on acid soils (varied habitats) in or near the southern Appalachians and Atlantic Coastal Plain, extending west to Ala. And e. Tenn. (W); it may be expected in se. Ky. H. interior (or densiflorum var. interior) is an extremely narrow-leaved (ca. 1-4 mm) plant typical of streambanks on calcareous soils in or near the southern Ridge-and-Valley region (D. Estes, pers. Comm.); it remains unknown in Ky. But occurs nearby in sw. Va. (Lee Co.) and perhaps central Tenn. (W).