Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Genus Description - Fls perfect; hypanthium short, hemispheric; cal irregular, 5-toothed; cor irregular, almost papilionaceous, but the upper petal the smallest and internal to the 2 upper lateral ones, the lower petals the largest, distinct; stamens 10, distinct; anthers versatile, longitudinally dehiscent; pods thin and flat, narrowly oblong, rather tardily dehiscent, several- seeded, strongly margined along the upper suture; trees or shrubs with simple, cordate, entire lvs and sessile fascicles of pedicellate fls borne on the stems of the previous year and opening before the lvs. 6, North Temperate.