Erythranthe glaucescens (nee Mimulus g.) - CNPS List 4 is, in your revised Jepson Manual (2012) - annual. Nesom (2012) also circumscribes Erythranthe glaucescens as annual. The type specimen of Erythranthe glaucescens is clearly an annual.
As Nesom noted (p. 61) Macnair (1996) "behaves as a perennial in the glasshouse". Furthermore, Nesom cited one specimen (Heller s.n. July 2, 1914) from "canyon Big Chico Creek" as a stoloniferous perennial.
Plants from the Middle Fork Feather River diversion dam, JEPS109856 (DWTaylor #19554) 6/28/2006 are without doubt perennial (see post August 3rd 2013)
Recently, Nesom (2013) discoursed on the duration races of other monkeyflowers: he observed E. microphylla to be invariably annual, while E. guttata was clearly perennial. The genomic mechanisms that integrate developmental patterns in higher plants must by definition differ greatly between annual and perennial plants (viz. the vernalization FLC gene pathway in Arabidopsis) - a rosette annual has to have genes that vernalization turns on about when its time...a fruit tree needs cold to fix other vernalization genes in preparation for flowering each spring...A Sequoiadendron needs to NOT fail to flower each and every year for 3,000 years (a rosette-bearing Sequoia is an extinct Sequoia).
Within monkeyflowers, a single natural taxon that switches between annual (or "facultative annual", if there is such a thing) and perennial duration is not likely. Darwin would not approve of the notion of a "facultative annual".
For this reason, perennial Erythranthe 'glaucescens' are best judged an undescribed species.
Below: plants from JEPS109856 under cultivation: note the stolons which grow in directly horizontal radius (grown in pots in sand, these plunged in water). The stolons grow laterally, rooting at the nodes readily, and in this instance, only become negatively geotropic once the side of the pot is reached.
Macnair, M.R. 1996. The Mimulus page. Pictures of Mimulus species. Mimulus guttatus complex.
Accessed Jan 2012.
Nesom, GL 2012. Phytoneuron 40:1-123.
Nesom, GL. 2013. Phytoneuron 2013-68:1-8
Thompson, D. 2012. Mimulus, pp. 988-998 in: Baldwin etc. revised Jepson Manual