This is a widespread northern and western species that extends south in the Appalachians to n. Ala. However, it has been confused in Ky. with the more southern species, illinoensis. P. amplifolius was not mapped in the state by FNA 22 but "to be expected." There is a coll. from LINC (PH) determined in 1953 by "H.A.W." as amplifolius, which needs rechecking. This coll. was made by C.W. Short in the 1830s in the "Dicks Rv near Crab Orchard", and was originally named P. lucens auct. (not L.). A recent coll. from Buck Creek in PULA (KNK) was referred to amplifolius by Clark et al. (2005), but this also needs to be rechecked. P. illinoensis is expected in the Dix Rv., since it is locally abundant in the Little South Fork, a similar stream to the south. Compared to close relatives, amplifolius differs in its submersed leaves, with more veins (19-49 versus <29) and distinctly arcuate; see also FNA 22.