Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Genus Description - Monoecious; pet and disk none; staminate fls with 4 valvate sep and 4–8 stamens, the filaments slender, the anthers elongate and often curved or coiled; pistillate fls with 3(–5) sep; styles slender, elongate, irregularly branched or lacerate into filiform segments; capsule (1–)3-locular; seeds with a caruncle; herbs, shrubs, or trees with alternate, petiolate, stipulate, usually serrate lvs and minute fls in axillary or terminal, often conspicuous, racemiform condensed cymose infls, each fl or fascicle of fls subtended by a bract; our spp. annual herbs blooming from July to Oct., with staminate fls only 0.5 mm wide and aggregated into axillary heads or short spikes, the pistillate fls with initially small but rapidly accrescent bracts that equal or exceed the mature pubescent frs. 400, mostly New World.