This occurs mostly in the southern Great Plains and lower Mississippi Valley (K). In Ky. it is largely restricted to old shallow ponds and slough margins in western regions, perhaps on relatively clayey soils with high base-status. FNA 26 suggested: "it is best adapted for growth in water less than 5 cm deep and is a poor competitor with the closely related H. rotundifolia in deeper waters." The only verified records from the Bluegrass regions are 1993 colls. from near Duncannon Pond in MADI (EKY); also 1840s colls. of C.W. Short and R.Peter from "Cole's Tavern on the Frankfort Road" [at intersection of US 62 and KY 1681] in WOOD (KY; see also GH and WIS). Short (GH) stated: "A very rare plant. I have only met with it at one locality." Natural ponds are rare in the Bluegrass region, and these two localities may have been frequented by bison or other large herbivores before settlement. The only possible record from Appalachian regions is BT's mapping in LAUR; however, no supporting coll. is known to exist. There has been confusion with rotundifolia in LARU and MEAD; see notes under rotundifolia. Flowers are generally white in Ky., but those in the MEAD population were blue (M).