Astragalus argophyllus Nutt. 

 Silverleaf milkvetch 



A. DESCRIPTION • ^- „ 



1 General description: See the preceding genus description. 

 These are prostrate plants with silvery-pubescent leaves and 

 relatively large purple flowers (slide 5 in Appendix E) . 



2 Diagnostic characters: The following combination of 

 characters separates this from other Montana species of 

 Astragalus (adapted from Dorn 1984): 



stems short or lacking 



silvery pubescent leaves ^ ■ ^^ ^ • v,^- 



leaflets more than 5, not awl shaped, with stiff straight 



hairs 

 hairs attached at base . 



stipules not united on side of stem opposite petiole 

 2-8 flowers per raceme 

 calyx 9-17 mm long 

 pods unilocular, not inflated, not thick wooly-hairy, 



without a stipe, more or less dorsoventrally 



compressed 

 ovaries and young pods pubescent 



B. GEOGRAPHIC DISTRIBUTION 



1 Species range: "Snake River, Idaho, south to Nevada and 

 eastern California, east to Montana, Wyoming, and Colorado 

 (Hitchcock and Cronquist 1973)." 



2. Montana distribution: Prior to this study the species was 

 known from ten sites in Beaverhead and Madison Counties. 



3. Occurrences in the study area: Five populations of A. 

 argophyllus were located, all of them in the southern part of 

 the study area within the Big Sheep Creek drainage. 



C. HABITAT ^ ,, 

 Barneby (1989) states that A. argophyllus var. argophyllus, to 

 which our material belongs, is restricted to "moist alkaline 

 or lowland meadow habitats." The known populations in the 

 study area occur in moist, often alkaline soils on lowland 

 floodplains and terraces at elevations ranging from 6,800 to 

 7,100 ft (see slide 5 in Appendix E) . Woody dominants at 

 these sites include Artemisia arbuscula, Artemisia cana, 

 Artemisia tridentata and Potentilla fruticosa. Dominant or 

 subdominant graminoids include Juncus balticus and Poa 

 nevadensis. These habitats are often subject to livestock 

 grazing. 



