This alga-like flowering plant of rocky riverine riffles is widely distributed from eastern North America to Central America, but it is generally absent from more eutrophic watersheds (K). It has fascinated botanists in Ky. and elsewhere since European settlement (Meijer 1976). Short (1836) noted: "the humble but useful Podostemum ceratophyllum, confined to the shoals of the most rapid rivers, where it serves to protect the channel from the fury of the current, by binding together gravel, shells, and stones, on one impenetrable mass." Podostemum has disappeared from several lower reaches of rivers in Ky., especially where impounded or locked-and-dammed. A. Michaux's type was from the Falls of the Ohio (JEFF) and C.W. Short also collected it here (CM); plants are now unknown in the Ohio Rv. bordering Ky. R. Peter (PH, Aug 1833 "on rocks in rapids") found it in the main stem of Kentucky Rv. (probably FAYE or MADI). Plants are now unknown in the Kentucky Rv. downstream of the forks at Booneville (OWSL), but it remains in the Red Rv. (POWE, WOLF) and other tributaries. It does remain locally abundant along the South Fork of Kentucky Rv., where flowers were collected in 1992 (KY). It also remains scattered along some tributaries of the Cumberland Rv., the Green Rv., the Licking Rv. and the Big Sandy Rv. It may have disappeared from the main stem of Cumberland Rv.. It was collected by several botanists from near the Falls here during 1939-1947, starting with E.L. Braun #2623 "in swift water at brink of Cumberland Falls" (F).