Astragalus barrii Barneby 

 BARRS MILKVETCH 

 Bean Family (Fabaceae) 



CONSERVATION STATUS 



U. S. Fish and Wildlife Service: None. It had once been considered a candidate for listing 

 (C2), but was dropped for being more common than originally known (3C). 



Bureau of Land Management: Watch. 



Montana Natural Heritage Program: G3 S3; Vulnerable because of rarity, both throughout 

 its range and in Montana. 



DESCRIPTION: Barr's milkvetch is a perennial that forms low, dense mats, with prostrate or 

 ascending stems up to 2 cm long from a woody rootcrown. Leaves have 3 narrowly lance-shaped 

 leaflets, are 1-4 cm long; and have membranous stipules. Leaves and stems are densely covered with 

 short white hairs. Purple or pinkish-purple flowers are borne in short stalked, narrow, open, few- 

 flowered inflorescences. Flower petals are 7-17 mm long and the calyx is 3-5 mm long and densely 

 covered with long, white hairs. The sparsely white-hairy pod is narrowly elliptical and 4-8 mm long 

 and 1-2 mm in diameter. Flowering in May to early June. The timing of flowering makes early 

 season surveys essential for locating populations of the species. 



Vegetatively, Barr's milkvetch is similar to other mat forming, 3-leaflet species of the genus in 

 Montana, tufted milkvetch {A. gilviflorus), summer orophaca (A. hyalinus), and Sweetwater 

 milkvetch {A. sericoleucus var. aretiodes). The first two of these species overlap with Barr's 

 milkvetch in their geographic distributions and flowering material is needed for positive 

 identiflcation. Astragalus gilviflorus and A. hyalinus have larger flowers with a calyx 6-16 mm, and 

 with whitish to cream colored corollas. They also have flower stalks (peduncles) which are short (< 

 3.5 mm) or absem, compared to Astragalus barrii peduncle length (7-24 mm). Astragalus gilviflorus 

 is widespread over the state and common. Astragalus hyalinus is occasional in Big Horn, Carbon, 

 Rosebud and Powder River counties; locally common in the Pryor Mountains; and A. sericoleucus 

 var. aretiodes is restricted to the Pryor Mountains. 



GEOGRAPHIC DISTRIBUTION 



Global distribution: Barr's milkvetch is a regional endemic known only from southeastern 

 Montana, southwestern South Dakota, and northeastern Wyoming (Heidel and Marriott 

 1996). 



Montana distribution: Southeastern Montana in Bighorn, Carter, Powder River, and 

 Rosebud counties. 



77 



