In some recent treatments, this widespread North American species (2n =66) has been combined with the Eurasian species, amphibia (FNA 5). But it should probably be recognized at least as P. amphibia var. emersa (Michx.) Hickman. Morphological and genetic differences may be small and gradual; deeper analysis is needed. In Ky., coccinea occurs usually along shorelines in stagnant water. It is unknown on the rocky riverbanks where amphibia sensu stricto has been found; see notes under that name. Based on F, coccinea differs in its pubescent peduncles and ochreolae (versus glabrous), more elongated leading spikes (4-18 x 0.7-1.5 cm versus 1-4 x 1-2 cm), and floating leaves relatively broad in shape with more rounded to cordate bases.