Mimulus rattanii is a species of monkeyflower known by the common name Rattan's monkeyflower. It is endemic to California, where it is known from the North and Central Coast Ranges. It grows in open and disturbed habitat types, such as rock outcrops and areas recently cleared by wildfire. It is endemic to California, where it is known from the North and Central Coast Ranges. It grows in open and disturbed habitat types, such as rock outcrops and areas recently cleared by wildfire. Mimulus rattanii is an annual herb growing 1 to 18 centimeters tall. The oppositely arranged oval leaves are up to 4. 6 centimeters long, the newer ones hairy in texture. The flower is no more than a centimeter long, its tubular base encapsulated in a swollen, ribbed calyx of hairy sepals. The flower is magenta in color, often with yellow markings in the mouth.