Fls unisexual, 4-merous, small, sessile in the axils of bracteal or foliage lvs, often aggregated into an emersed terminal spike; cal of 4 teeth, or obsolete; pet present or not; stamens 8 or 4 (even in one sp.); fr hard, ±4-lobed, eventually splitting into 4 mericarps; vegetatively plastic herbs, submersed in quiet water or rooting on muddy shores, usually with once-pinnately dissected lvs. 20+, cosmop.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.