Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Genus Description - Very much like Astragalus, except for the abruptly short-beaked keel; fr sessile, ovoid to cylindric, sulcate on the upper side and partly or wholly 2-locular by intrusion of the sutures; perennial herbs, acaulescent or nearly so, the lvs and peduncles crowded on a multicipital caudex surmounting a taproot; stipules in our spp. adnate to the petiole; fls purple to ochroleucous, in dense spikes or heads on long axillary scape-like peduncles; our spp. becoming 1–4 dm. 300, N. Temp.