Erythranthe cardinalis, the scarlet monkeyflower, is a flowering perennial in the family Phrymaceae. Together with other species in Mimulus section Erythranthe, it serves as a model system for studying pollinator-based reproductive isolation. It was formerly known as Mimulus cardinalis.
It is a fairly large, spreading, attractive plant which bears strongly reflexed, nectar-rich red or orange-red flowers and toothed, downy leaves. It is native to the West Coast and Southwestern United States and Baja California, and is generally found at low elevation in moist areas. Occasional populations of yellow-flowered Erythranthe cardinalis (which lack anthocyanin pigments in their corollas) are found in the wild.
Erythranthe cardinalis is cultivated in the horticulture trade and widely available as an ornamental plant for: traditional gardens; natural landscape, native plant, and habitat gardens; and various types of municipal, commercial, and agency sustainable landscape projects. Cultivars come in a range of colors between yellow and red, including the "Santa Cruz Island Gold" variety, originally collected from Santa Cruz Island off the coast of California.
Its blooms and large nectar load attract hummingbirds, whose foreheads serve as the pollen transfer surface between flowers. In the area where it overlaps with its sister species, Erythranthe lewisii, reproductive isolation is maintained almost exclusively through pollinator preference.