This name is a synonym of Mimulus guttatus var. gracilis (A. Gray) G.R. Campb..
The record derives from Tropicos
(data supplied on 2012-04-18)
which reports it as a synonym (record 50102039) with original publication details: Rep. U.S. Mex. Bound. 2(1): 115–116 1859.
Full publication details for this name can be found in IPNI: http://ipni.org/urn:lsid:ipni.org:names:162277-2.
This name was in version 1 of The Plant List, record tro-50102039, and has not been changed.