Black Alder, European Alder, European Black Alder: Alnus glutinosa - Non-native, not naturalized.
Gray Alder, Mountain Alder, Thinleaf Alder: Alnus incana ssp. tenuifolia (Synonyms: Alnus incana var. occidentalis, Alnus incana var. virescens, Alnus occidentalis, Alnus xpurpusii, Alnus rugosa, Alnus rugosa var. occidentalis, Alnus tenuifolia, Alnus tenuifolia var. occidentalis) -
California Alder, White Alder: Alnus rhombifolia (Synonym: Alnus rhombifolia var. bernardina) -
Hybrid Red-White Alder: Alnus rhombifolia x Alnus rubra -
Oregon Alder, Red Alder: Alnus rubra (Synonyms: Alnus oregona, Alnus oregona var. oregona, Alnus oregona var. pinnatisecta, Alnus rubra var. pinnatisecta) -
Green Alder, Mountain Alder, Siberian Alder, Sitka Alder, Wavy-leaf Alder: Alnus viridis ssp. sinuata (Synonyms: Alnus alnobetula, Alnus crispa ssp. laciniata, Alnus crispa ssp. sinuata, Alnus sinuata, Alnus sitchensis, Alnus viridis ssp. fruticosa, Alnus viridis var. sinuata, Duschekia sinuata) - Note: This taxon is recognized as Alnus alnobetula ssp. sinuata in Oregon (2022).