Haresfoot or rabbitsfoot milkvetch (Astragalus purshii var. lagopinus) is closely related to the locally common woolly-pod milkvetch (A. purshii var. glareosus), which is widespread in the Boise Front.  It differs in being more compact, with smaller flowers and smaller fruits.  Locally it is apparently restricted to shallow soil on exposures of a crumbly, vescicular, late Miocene basalt (S. Wood, pers. comm. 2024) localized near Lucky Peak Dam.

The distinctiveness of the plants in this area was not realized until 2011, when the unusually compact habit caught my attention.  The specimens I collected seemed to fit var. lagopinus best, using the keys by Astragalus specialist Rupert C. Barneby (1964, 1989).  In Barneby’s treatments, however, var. lagopinus was known only from central Oregon, adjacent northeastern California, and northwestern Nevada.  Not only did this make the Lucky Peak population a significant range extension, but it also split the geographic distribution of var. lagopinus on both sides of another small-flowered variety:  the rare Snake River milkvetch, Astragalus purshii var. ophiogenes. endemic to the Snake River and tributaries in southwestern Idaho and adjacent Oregon.

About this same time, Don Mansfield at The College of Idaho had been finding some plants from Owyhee County that also fit the description of var. lagopinus better than var. ophiogenes.  As a result, he encouraged one of his students, Betsaida Chavez Garcia, to undertake a morphometric analysis of typical var. lagopinus, typical var. ophiogenes, and the anomolous plants from near Lucky Peak Dam and Owyhee County.

The results were presented as a poster, “Morphological analysis of small-fruited varieties of Astragalus purshii (Fabaceae) confirms varietal distinction”.

officially added to Idaho Rare Plant list in 2016 as S1