Two related species of Trifolium L. endemic to western North America, T. variegatum Nutt. s. l. and T. polyodon Greene, are studied. Multivariate analyses and morphological differences suggest that three species should be recognized instead of two. Trifolium variegatum is divided into two species: T. appendiculatum Lojac. and T. variegatum. Trifolium appendiculatum (including T. rostratum Greene) is a large-flowered species endemic to California and southern Oregon. Trifolium variegatum is found throughout western North America and remains the most diverse, but is now circumscribed by a consistent floral morphology. Trifolium polyodon is restricted to the Monterey peninsula and has distinctive calyx lobe teeth; its circumscription remains unchanged.