This name is a synonym of Penstemon rydbergii var. aggregatus (Pennell) N.H. Holmgren.
The record derives from Tropicos
(data supplied on 2012-04-18)
which reports it as a synonym (record 29204279) with original publication details: Contr. U.S. Natl. Herb. 20(9): 367–368 1920.
Full publication details for this name can be found in IPNI: http://ipni.org/urn:lsid:ipni.org:names:187125-2.
This name was in version 1 of The Plant List, record tro-29204279.