Cal obscurely nerved, strongly bilabiate, with entire lips, bearing a prominent transverse appendage on or proximal to the upper lip; cor 2-lipped, the upper lip generally ±galeate, the lateral lobes of the lower lip somewhat separated from the broad central lobe and marginally partly connate with the upper lip; stamens 4, ascending under the upper lip, the anthers of the upper pair with 2 pollen sacs, those of the lower pair with only one; style gynobasic, its upper branch reduced or wanting; ours all perennial, mostly rhizomatous; fls blue or violet, seldom pink or white, solitary in the axils or in terminal or axillary racemes. 300, cosmop.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.