Apios Fabr.

Cal-tube broadly hemispheric, the 4 upper lobes very short or obsolete, the lowest one lance-triangular, about equaling the tube; standard rotund, soon reflexed, obscurely auricled near the base; wings curved-oblong-obovate, soon deflexed below the keel, short-clawed, auricled at the base of the blade; keel-pet strongly curved, horseshoe-shaped, blunt, broadest at the truncate base; stamens 10, diadelphous; style glabrous, curved with the keel; fr linear, several-seeded, coiled after dehiscence; perennial twining herbs from slender rhizomes bearing tuberous thickenings, with pinnately compound lvs of 5–7 obscurely stipellate lfls and axillary peduncled racemes, the nodes bearing prominent callous thickenings; each fl closely subtended by a pair of caducous, linear, 1-nerved bractlets. 10, e. Asia and e. U.S.