This name is a synonym of Alnus incana subsp. tenuifolia (Nutt.) Breitung.
The record derives from WCSP
(data supplied on 2012-03-23)
which reports it as a synonym (record 6440) with original publication details: Vasc. Pl. Pacif. N.W. 2: 73 1964.
This name was in version 1 of The Plant List, record kew-6440.