Rhizomatous, functionally dioecious perennial, aquatic or amphibious or terrestrial, the terrestrial forms erect or ascending, to 1(-2) m, with hairy, typically lance-acuminate lvs, the more strongly aquatic forms with floating branches (and often stolons) and lvs, the lvs then glabrous, typically elliptic and obtuse or rounded; ocreae with or without a bristly fringe, in aerial forms often with a flared collar; racemes stout, dense, mostly 2-15 נ1-2 cm, usually borne singly or in pairs at the tips of major branches; tep 5, pink or red, bluntly rounded above, united below, 4-5 mm at anthesis, to 7 mm in fr, becoming veiny and enclosing the achene, this dark, shiny, doubly convex, 2.5-3 mm; 2n=66, 96, 98. Widespread in the N. Hemisphere, and in S. Afr. Our members of the species may be organized into 2 copiously intergrading ecotypic vars. The aquatic-adapted extreme, var. stipulaceum N. Coleman, flowers only when in water; its infls are to 4 cm, and the lvs are typically glabrous, floating, and elliptic. (P. natans; P. hartwrightii) The terrestrial-adapted extreme, var. emersum Michx., grows on land or is strongly emergent from shallow water, and does not produce floating leaves or shoots; its infls are 4-15 cm, the lvs are hairy and acuminate, and the peduncles are glandular-hairy. (P. coccineum; P. muhlenbergii). Var. amphibium is strictly Eurasian. (Persicaria a.)
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.