Within the genus Cercocarpus H.B.K., commonly called mountain mahogany, there are three species, C. monanus Raf., C. ledifolius Nutt., and C. intricatus S. Wats., that occupy rather distinct habitats in Utah. During the past two years a study of Cercocarpus populations growing throughout Utah has shown not only that hybridization does occur between all three species but that in some instances viable progeny are produced from these F1 hybrids. Despite rather severe isolation barriers, there is sufficient plasticity to permit inter-breeding under certain circumstances.