This globally rare species of larger streams in the central Appalachian has been overlooked in Ky., although it was mapped here by FNA 22. It is close to epihydrus (which was apparently combined by Cr and other authors) and to diversifolius; some intergradation is suspected. P. tennesseensis is distinct from diversifolius in its larger floating leaves (ca. 8-12 mm wide) with more acute tips; also, stipules are partly adnate to leaves (FNA 22). Some 1830s colls. of C.W. Short from "Kentucky Rv." are obscure or need to be rechecked, but are tentatively mapped here in FAYE. They were initially labelled "heterophyllum" or "acutifolium" but filed under epihydrus (at KY), natans (at MICH) or gramineus (at GH). The only other coll. made in the Kentucky Rv. watershed is from CLAY (GH): E.L. Braun s.n., 7 Jul 1933, Red Bird River, quiet parts of stream. More recently, tennesseensis has been collected in the Cumberland Rv. watershed: Marsh Cr. of MCRE (KY). It has been suspected in the Rockcastle Rv. of LAUR and ROCK, a few riffles below Livingston (sight records of JC and T. Bloom, KSNPC). In Tenn., it occurs in tributaries of the Big South Fork, which flows into Ky. through MCRE (Ch).