Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Genus Description - Fls small, perfect or unisexual; cal at anthesis deeply 5- lobed, at maturity unchanged except in size, or some or all lobes becoming carinate, cucullate, or winged; stamens 5; ovary depressed or flattened; styles 2–5, short; fr completely enclosed by the cal; pericarp thin and delicate, usually loose; seed commonly horizontal, occasionally vertical; embryo spirally coiled; perisperm scanty or none; herbs (our spp. all annual) with very numerous, linear lvs, the upper reduced to bracts, forming terminal spikes and bearing in the axils the solitary or clustered (commonly 3) fls. (Dondia) The taxonomy of the genus is in need of careful reconsideration. 50, widespread.