Astragalus platytropis

Broad-keeled milkvetch is a small perennial herb without prolonged stems; all leaves are clustered at the base of the plant on short branches of the rootcrown clothed with old leaf stalks. Pinnately compound leaves, 1-9 cm long, have 7-15 oblong to elliptic, often blunt-tipped leaflets. Foliage is sparsely covered with gray or silver hairs. Spreading flower stalks arise from amongst the leaves and bear 3-9 flowers near the tip. Whitish, pea-like flowers are 6-9 mm long with an upper petal that is barely reflexed and nearly the same length as the others. The calyx is 3-5 mm long and sparsely covered with white or black hairs. Inflated, egg-shaped fruits are papery, purple-mottled, and 15-33 mm (ca. 1 in) long. Fruits that resemble small Chinese lanterns are usually found on the ground near the base of the plant.

It resembles the widespread ASTRAGALUS MISER VAR. HYLOPHILUS in vegetative condition, except that it has leaves with petioles that are usuallly much longer than the blade, and typically has a trailing growth form. The only other species of milkvetch in Montana with inflated pods that lie along the ground is ASTRAGALUS CRASSICARPUS, but it differs in having a papery pod with a mottled pattern rather than a very fleshy green or red pod. papery, purple-mottled fruit are diagnostic.

This species occurs in rocky areas, on ridge tops, and in scree fields near or above the timberline at elevations ranging from 6,000 to 12,000 feet (ASW 2022, FNA 2023)