Mimulus johnstonii is a species of monkeyflower known by the common name Johnston's monkeyflower. It is endemic to the Transverse Ranges of southern California, where it is known only from the San Gabriel and San Bernardino Mountains. It grows in rocky and disturbed habitat, such as roadsides and scree. It is endemic to the Transverse Ranges of southern California, where it is known only from the San Gabriel and San Bernardino Mountains. It grows in rocky and disturbed habitat, such as roadsides and scree. Mimulus johnstonii is an annual herb producing a thin, hairy stem up to about 20 centimeters tall. The oppositely arranged pointed oval leaves are 1 to 3 centimeters in length. The tubular base of each flower is encapsulated in a reddish, hairy calyx of sepals with spreading, pointed lobes. The flower is dark pink to magenta in color with a yellow spot and usually two purple spots in its throat. It is up to 1. 5 centimeters long and has five lobes at its mouth.