This name is a synonym of Euphorbia vallis-mortuae (Millsp.) J.T.Howell.
The record derives from WCSP
(data supplied on 2012-03-23)
which reports it as a synonym (record 38283) with original publication details: Publ. Field Mus. Nat. Hist., Bot. Ser. 2: 403 1916.
Full publication details for this name can be found in IPNI: http://ipni.org/urn:lsid:ipni.org:names:340874-1.
This name was in version 1 of The Plant List, record kew-38283, and has not been changed.