Astragalus purshii var. lagopinus   haresfoot or rabbitsfoot milkvetch
           
  
Fabaceae (Alt: Leguminosae )
sensitive                      herbaceous           
Distribution: Oregon Trail

UW Burke Herbarium Link: Astragalus purshii var. lagopinus
USDA Plants Link: Astragalus purshii var. lagopinus   (ASPUL)


rabbitsfoot milkvetch (Astragalus purshii var. lagopinus)

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.  In the Boise Front 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.  It is quite possible that the majority of this habitat was destroyed during the construction of the dam and subsequent modifications, with the remaining plants only a small remnant of the original occurrence.

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”, at the Idaho Academy of Sciences in 2013.

The study involved a Principle Components Analysis of 13 characters from 103 specimens, including leaflet number and length, flower number and size, and pod curvature.  The results supported the continued recognition of var. ophiogenes (blue) and var. lagopinus (red) as separate varieties, but with possible clinal variation in the area of geographic overlap.  Intriguingly, the Lucky Peak Dam samples (maroon) formed a peripheral cluster contiguous to core populations of var. lagopinus, suggesting that they may best be treated as a distinct but currently unrecognized variety.

Although no further research on the taxonomic status of the Lucky Peak Dam populations has been undertaken,  A. purshii var. lagopinus was officially added to Idaho Rare Plant list in 2016, with an S1 (Critically Imperiled) status in Idaho (https://explorer.natureserve.org/Taxon/ELEMENT_GLOBAL.2.133552/Astragalus_purshii_var_lagopinus).

Barneby, R. C.  1964.  Atlas of North American Astragalus.  Mem. New York Botanical Garden 13: 1–1188.

Barneby, R. C.  1989.  Fabales.  Intermountain Flora: Vascular Plants of the Intermountain West, U.S.A. 3B: 1–279.






Trail guides, walks or articles that mention Astragalus purshii var. lagopinus