Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Genus Description - Fls asymmetrical; sep small, appressed; pet elongate, ± connivent, the upper one of the 2 outer ones spurred at the base, at the apex somewhat dilated and keeled or winged, the lower one narrower, similarly dilated and keeled, but not spurred at the base (sometimes gibbous), the 2 inner (lateral) pet narrower, similarly dilated and keeled or winged, and coherent over the stigma; capsule slender, often torulose, 2- valved, with a persistent replum and a slender, persistent style; seeds black, shining, minutely low-tuberculate; herbs with cauline, alternate, bipinnately dissected lvs and short, bracteate racemes of short-pediceled fls. (Capnoides) 300, mainly N. Temp.