Gray Alder, Mountain Alder, Thinleaf Alder, Thin-leaf Alder: Alnus incana ssp. tenuifolia (Synonyms: Alnus incana var. occidentalis, Alnus incana var. virescens, Alnus x purpusii, Alnus tenuifolia) -
Mountain Alder: Alnus viridis ssp. crispa (Synonyms: Alnus crispa, Alnus crispa var. elongata, Alnus crispa var. mollis, Alnus x hultenii, Alnus viridis var. crispa) -
Siberian Alder, Green Alder, Mountain Alder: Alnus viridis ssp. fruticosa (Synonym: Alnus viridis var. fruticosa) -
Sitka Alder: Alnus viridis ssp. sinuata (Synonyms: Alnus alnobetula, Alnus crispa ssp. laciniata, Alnus crispa ssp. sinuata, Alnus sinuata, Alnus viridis var. sinuata) -