Comprehensive reevaluation of both herbarium specimens and field observations of the North American Thermopsis leads to our recognition of 10 species. Three species occur in the southern Appalachians: T. villosa, T. mollis, and T. fraxinifolia. The Rocky Mountains and intermountain regions are populated by the relatively variable and widespread species T. divaricarpa, T. montana, and T. rhombifolia. The Pacific coastal mountains of California are dominated by the variable T. californica (with three infraspecific taxa), which gives way to T. gracilis in northern California and western Oregon. Thermopsis macrophylla and T. robusta have restricted ranges in California.