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 and as an illegitimate name (record 6461) with original publication details: Bot. California 2: 81 1880.
Full publication details for this name can be found in IPNI: http://ipni.org/urn:lsid:ipni.org:names:9426-2.
This name was in version 1 of The Plant List, record kew-6461.