Mimulus rubellus is a species of monkeyflower known by the common name little redstem monkeyflower. It is native to western North America, including the southwestern United States to Wyoming and Texas, and into Baja California. It is native to western North America, including the southwestern United States to Wyoming and Texas, and into Baja California. Mimulus rubellus is an annual herb growing 2 to 32 centimeters tall with a very slender, red stem. The oppositely arranged oval leaves are up to 3 centimeters long and lance-shaped to oval, the lower ones borne on short petioles. The herbage is usually lightly hairy and green to reddish in color. The petite tubular flower is no more than a centimeter long, the base of its tube encapsulated in a narrow, ribbed calyx of sepals. The flower may be yellow or pink in color and the mouth of the flower is usually dotted with red or purple.