Physiological Differentiation in Astragalus With Reference to Selenium

Sa m F. T'release a n d Helcn M. Trcl ca scSO~IE SPEC IES of Astragalus appear t o be d efinit e se len ium indicators, occ ur ri ng-on ly on selen ifero us so ils an d always contai ning sel en ium wh en collect ed in the field ( Beat h, E ppson, an d Gilbert, 1935, 19 39a, 1939b ) .Other s pecies of Astragalus, howev er, are n ot li m it ed t o selen if erous soils .E ven whe n growing-on suc h soils in proximity to sel en ium-accum ul atin g species, t h ese are f ree fro m se len ium or conta in ve ry lo w concen t rat ions .Si n ce two of the seleni um indicators-Astragal us racem osu s and Astragalus patt ersonii-we re fo und t o be g re a tly Fi g. 1-g.-F ig. 1 (above) .A st raga l ll .~crass ica r pu8 Nutt.(prairie ap ple) growi ng on th e Chugwate r for mation of the Triassic system about 7 miles east of Laramie, Wyoming.This species occurs on hot h selenif erous and non-selenif erous soils.-Fig.Z (below).As tru.qnlu rac e-1/10811 8 Pu rsh growing on th e P ierre formation of t he Cretaceous svs t em 15 miles sout h of Pierr e, South Dakota.W he n ai r-d ry , thi s specimen contained 3,9:20 ppm. of selenium.This species is a s elenium indicator plant, appa rently occur r ing only on selenifero us soils.