Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Genus Description - Monoecious; cal 3–6-lobed; pet none; disk small or none; stamens 2–5+; ovary with 3 locules and ovules; styles connate at base, recurved-spreading above, undivided; capsule 3- lobed; seeds without a caruncle; perennial herbs or half-shrubs, often twining, ± pubescent, often with some stinging hairs; infls slender, racemiform, lf-opposed or terminating leafy-bracteate axillary branches, with a few pistillate fls below and many staminate ones above. 100+, mostly tropical.