This name is a synonym of Penstemon attenuatus var. palustris (Pennell) Cronquist.
The record derives from Tropicos
(data supplied on 2012-04-18)
which reports it as a synonym (record 50119025) with original publication details: Notul. Nat. Acad. Nat. Sci. Philadelphia 71: 8–9 1941.
Full publication details for this name can be found in IPNI: http://ipni.org/urn:lsid:ipni.org:names:187641-2.
This name was in version 1 of The Plant List, record tro-50119025.