Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Genus Description - Sep ascending; pet yellow or white, spatulate to obovate, small, often scarcely exceeding the sep, gradually narrowed to the claw; short stamens flanked at base by a pair of minute glands, or these confluent into an annular gland; long stamens separated by a short conic gland; ovary cylindric; style very short; stigma capitate or shortly 2-lobed; ovules numerous; fr subterete, subglobose to cylindric, with short style and persistent stigma, the valves thin, with obscure midnerve; seeds numerous, minute, in most spp. in 2 rows in each locule; annual to perennial herbs with toothed to pinnatifid lvs, the pubescence of simple hairs or none. 80, cosmop.