This name is a synonym of Helianthus nuttallii subsp. rydbergii (Britton) R.W.Long.
The record derives from TICA
(data supplied on 2012-02-11)
which reports it as a synonym (record A2447E9C-03D1-406A-93F3-ABD980E8FDF2) with original publication details: 74 1972.
Full publication details for this name can be found in IPNI: http://ipni.org/urn:lsid:ipni.org:names:119198-2.
This name was in version 1 of The Plant List, record gcc-62084, and has not been changed.