This rhizomatous herb occurs in somewhat disjunct calcareous or dolomitic sections of east-central states. H. sphaerocarpon has often been confused with dolabriforme, especially without its distinctively smaller flowers. Its leaves tend to be deeper glossy-green above (versus generally glaucous) and wider (mostly 3-10 mm versus 2-6 mm), the larger ones often with a clasping base; plants usually (despite Cr and Y) grow into open patches (versus clustered stems with little or rhizome). Although sphaerocarpon was described from Ky. by F.A. Michaux in 1803 and listed by Short (1837), the name was not widely used in the state until Braun in 1943; Rafinesque appears to have used some other obscure name for this species (perhaps his riparium; Merrill 1949). There was early confusion in nomenclature with H. ellipticum Hook. (a more northern species), H. cistifolium Lam. (which occurs only on the southeastern Coastal Plain) and perhaps H. nudiflorum (Gray 1864, 1878; Small 1933). H. sphaerocarpon varies greatly in overall stature and leaf width, from drier to damper habitats, but no segregates have been recently recognized. Plants from the Bluegrass region of Ky. (e.g. from the Kentucky Rv. Palisades) tend to have smaller flowers than more southern plants (e.g. from the Cumberland Rv. bluffs): with petals about 4 x 2 mm versus 6-7 x 3-4 mm. Plants from the Ozark region tend to have wider leaves than plants from the Interior Low Plateaus (St): mostly 5-18 mm wide (versus 2-7 mm), with more distinct lateral veins, narrowly oblong to elliptic (versus linear), and flat-margined (versus somewhat revolute). The best name for these Ozarkian plants remains uncertain (Y; A. Floden, pers. comm.).