Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Genus Description - Cal tubular, membranous, deeply divided into 2 lateral halves; cor-tube slender, elongate, scarcely dilated distally, the upper lip (galea) triangular-acuminate, laterally compressed, the lower lip much shorter than the upper, appressed or deflexed; stamens 4, paired, ascending under the galea, included; one pollen-sac attached at its center, the other suspended from its summit; stigma capitate or shallowly 2-lobed; fr ovoid or oblong, loculicidal; hemiparasitic herbs with alternate, often pinnatifid lvs and large fls in dense terminal spikes, each fl subtended by a large, entire or pinnatifid, sometimes brightly colored bracteal lf. 150+, mostly w. N. Amer.