European Mountain-ash, European Mountain Ash, Rowan: Sorbus aucuparia (Synonym: Pyrus aucuparia) -
Cascade Mountain Ash, Cascade Mountain-ash, Greene's Mountain Ash, Rocky Mt. Mountain Ash: Sorbus scopulina (Synonyms: Pyrus scopulina, Sorbus cascadensis, Sorbus scopulina var. cascadensis, Sorbus scopulina var. scopulina) - Small tree to 12 feet. Flowers small, white, in round clusters like an overturned plate (cyme). Leaves compound pinnate, very shiny, with small serrations.
Dwarf Mountain Ash, Gray's Mountain Ash, Sitka Mountain-ash, Sitka Mountain Ash: Sorbus sitchensis var. grayi (Synonyms: Pyrus occidentalis, Pyrus sambucifolia var. pumila, Sorbus occidentalis, Sorbus pumilus, Sorbus sambucifolia var. pumila, Sorbus sitchensis ssp. grayi) - Small tree to 12 feet. Flowers small, white, in round clusters like an overturned plate (cyme). Leaves compound pinnate, a dull blue-green, with small serrations, the serrations on the upper half of the leaflets.
Sitka Mountain-ash, Sitka Mountain Ash: Sorbus sitchensis var. sitchensis (Synonym: Sorbus americana var. sitchensis) - Evidently only east of the Cascades in northeastern Washington. Small tree to 12 feet. Flowers small, white, in round clusters like an overturned plate (cyme). Leaves compound pinnate, a dull blue-green, with small serrations, the serrations from below the midpoint of the leaflets to the tip.