This name is a synonym of Washingtonia ambigua (A. Gray) J.M. Coult. & Rose.
The record derives from Tropicos
(data supplied on 2012-04-18)
which reports it as a synonym (record 50095824) with original publication details: Rev. N. Amer. Umbell. 119 1888.
Full publication details for this name can be found in IPNI: http://ipni.org/urn:lsid:ipni.org:names:177035-2.
This name was in version 1 of The Plant List, record tro-50095824.