Cascade Mountain-ash: Sorbus hybrid (grayi X scopulina) - These plants (from above 6500' in Hellroaring Valley) have combined leaf and bud traits of the two parents.
Cascade Mountain-ash, Greene's Mountain-ash, Rocky Mountain Mountain-ash, Western Mountain-ash: Sorbus scopulina (Synonyms: Pyrus scopulina, Sorbus cascadensis, Sorbus scopulina var. cascadensis, Sorbus scopulina var. scopulina) -
Gray's Mountain-ash, Sitka Mountain-ash: Sorbus sitchensis var. grayi (Synonyms: Pyrus sambucifolia var. pumila, Sorbus occidentalis, Sorbus pumilus, Sorbus sambucifolia var. pumila, Sorbus sitchensis ssp. grayi) -