Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Genus Description - Fls unisexual (the plants monoecious or rarely dioecious) or some of them perfect; receptacle large, convex; sep 3, reflexed in fr or persistently erect or spreading; pet 3, deciduous, white; stamens 7–many; pistils numerous, aggregated into a subglobose head on a large receptacle, appearing to be spirally arranged; achenes flattened, winged at least on the margins; infl racemose, with 1–12 mostly 3-fld whorls, each whorl subtended by 3 bracts, occasionally with floriferous branches substituting for fls at the lowest whorl(s), or the fl solitary and terminal in depauperate plants; rooted annual or perennial aquatics, the infl and usually also the lvs emersed; rhizomes sometimes with apical tubers. The lvs are all basal, typically with an aerial, expanded, often sagittate blade on a petiole about as long as the water is deep. In deep or swiftly moving water, wholly submersed lvs are produced by some spp.; these often take the form of ribbon-like bladeless phyllodia (the flattened petioles). Similar short, stiff phyllodia are produced in tidal sites. 25+, cosmop., mainly New World. (Lophotocarpus)