16 



Astragalus platytropis Gray 



BROAD-KEELED MILKVETCH 



Bean Family (Fabaceae) 



CONSERVATION STATUS 



U.S. Fish and Wildlife Service: None. 



Bureau of Land Management: Broad-keeled milkvetch was considered for watch status 

 on the draft list circulated in the spring of 1995. 



Montana Natural Heritage Program rank: G5 S2 (imperiled) prior to this study; reranked 

 following this study to S3 (vulnerable), and moved the watch list as a species of limited 

 distribution. 



DESCRIPTION: Broad-keeled milkvetch is a small perennial herb with leaves clustered at the 

 base of the plant on short branches of the rootcrown clothed with old leafstalks. 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. Flower stalks arise among 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. The inflated fruits lie along the ground when they mature and 

 are conspicuously purple-mottled, papery, and 15-33 mm long, resembling small Chinese 

 lanterns (Figure 7, Appendix D-1). The fruit mature in the latter half of June and persist at least 

 tliiough July. 



Superficially, broad-keeled milkvetch resembles the widespread Astragalus miser var. hylophilus 

 in vegetative condition, except that it has leaves with petioles usually 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 the widespread Astragalus crassicarpus (ground 

 plum), which has a very fleshy green or red pod rather the papery-textured, mottled pod of ^. 

 platytropis. 



GEOGRAPHICAL DISTRIBUTION 



Global distribution: Nevada and California to western Utah, with disjunctions in 

 southeastern Oregon, east-central Idaho, and southwestern Montana. 



Montana distribution: Centered in one contiguous area of southwestern Montana in 

 Beaverhead, Madison and Silver Bow counties. It is found in valley margins and 

 foothills to montane slopes in and between the East Pioneer Mountains, Highland 

 Mountains, and Tobacco Root Mountains (Figure 8). 



