Stems clustered on the surficial crown of a taproot, 1-5 dm, glabrous or thinly strigose; lower stipules large and veiny, the upper smaller and spreading or deflexed; lfls 7-17, oblong or elliptic, 1-2 cm, glabrous on both sides or sparsely strigillose beneath; racemes at anthesis compact, 2-3 cm, later elongating; cal-tube black-hairy, 3-3.5 mm, the lobes subulate, half as long; wings and keel progressively shorter than the standard; fr black-hairy, reflexed, oblong or slightly curved, obscurely and bluntly trigonous, flattened or depressed on the lower side but hardly sulcate, the lower suture intruded to form a narrow partial partition; stipe 2-5 mm; 2n=16, 32. Local on shelving limestone along rivers or in the mts.; Nf. and Lab. to N.S. and Vt., and widespread in the w. cordillera. (Atelophragma r.) Var. robbinsii, with relatively small whitish fls ca 9 mm, and with obscurely strigose fr 10-15 mm, formerly occurred near Burlington, Vt., but is now thought to be extinct. Var. minor (Hook.) Barneby, widespread in the w. cordillera, and occurring from Lab. and N.S. to Vt., has the lfls strigose beneath, purple fls 10-12 mm, and conspicuously strigillose fr 13-25 mm, short-acuminate but scarcely beaked. (Var. blakei) Var. jesupii Eggl., occurring along the Connecticut R. in Vt. and N.H., differs from var. minor in that the lfls are glabrous or nearly so beneath, and the thinly strigulose fr ends in a slender beak 1.5-3 mm. Other vars. occur to the n. and w.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.