Mimulus rubellus is a diminutive annual herb with white and pink flowers with pink spots within the corolla tube. The corolla lobes are notched. The sessile leaves have one or two pairs of teeth or are entire. The calyx and herbage is stipitate glandular with sand and dirt readily sticking. Although this species is apparently more common in the mountains (as supported by specimens from the Pinos Altos area in the Dale A. Zimmerman Herbarium,) it can also found in the leaf cover under mesquite in the lower elevation arid areas after a moist winter.