This name is a synonym of Penstemon procerus var. modestus (Greene) N.H. Holmgren.
The record derives from Tropicos
(data supplied on 2012-04-18)
which reports it as a synonym (record 29204285) with original publication details: Leafl. Bot. Observ. Crit. 1(12): 165 1906.
Full publication details for this name can be found in IPNI: http://ipni.org/urn:lsid:ipni.org:names:187498-2.
This name was in version 1 of The Plant List, record tro-29204285.