This species is close to limosa, with somewhat similar habitat and range, but it occurs mostly in ponds of the central Great Plains and it is absent in the lower Mississippi Valley. The only verified records for Ky. are the following two colls.: (1) F.T. McFarland #43, 15Aug1943, from "shallow pond on Morrison Farm, 2 miles N of Hodgenville" in LARU (GH, MO, NY, TENN, etc.); (2) A.L. Hotchkiss #2003, 17Aug1961, from "dark gray mucky soil, in shallow water of sinkhole ponds near Doe Run" in MEAD (GH, NCU, TENN etc.). There has been confusion with limosa, and some authors have combined these taxa as varieties of limosa sensu lato. A few of the herbarium sheets from MEAD appear to be mixed colls. or intermediate in morphology (GH, VCU). H. rotundifolia differs from limosa sensu stricto as follows (FNA 26, W): vegetative stems commonly elongating unless plant emersed from early age (versus only on plants in over 5 cm of water); petiolate leaf blade round to oblong (versus oblong to ovate), base cordate to truncate (versus truncate to cuneate); perianth with 11-29 mm tube (versus 15-45 mm), and its distal central limb lobe with lateral flanges (versus without lateral flanges). Both taxa can have blue or white flowers.