Apparent polyphyly within the unresolved clade of Lomatium (Apiaceae) containing L. triternatum, L. anomalum, L. thompsonii, and L. packardiae suggests conflict among current taxonomic classification schemes. To recover this clade and more clearly define species boundaries, we examined populations of L. anomalum from three geographic regions in Idaho and adjacent Oregon. Using phylogenetic, morphological, and ecological data, we conclude that the L. anomalum complex currently circumscribes multiple species. Phylogenetic analysis of the nuclear ribosomal ITS and ETS, and cpDNA rpl32-trnLUAG, rps-16 intron, trnD-trnT, ndhA intron, and psbA-trnH recovered populations from the Boise foothills as a distinct, monophyletic clade. Principal Components Analysis of 30 reproductive and vegetative characters show two distinct groups: one of Boise foothills and one of the combined Mann Creek and Camas Prairie vicinities. Principal Components Analysis of 16 soil characteristics show that soils occupied by Boise foothills populations are distinct from those occupied by Mann Creek and Camas Prairie populations. Based on phylogenetic, morphometric, and ecologic criteria, populations of what had been considered L. anomalum from the Boise foothills and vicinity are here described as a new species—Lomatium andrusianum.