Mimulus evanescens is a rare species of monkeyflower known by the common name disappearing monkeyflower. It is native to the western United States, where it is known from about ten locations in and around the Great Basin within the states of Idaho, Oregon, and California. Specimens of the plant had been catalogued as Mimulus breviflorus, but on further examination it was evident that they were a separate, unclassified species; this was described to science in 1995. It is thought that the plant may have evolved via hybridization between M. breviflorus and M. latidens, or that M. evanescens evolved from M. latidens and then into M. breviflorus. M. evanescens is a succulent annual herb coated with tiny glandular hairs and having a somewhat slimy texture. The thin stems grow mostly erect to a maximum height near 25 centimeters. The leaves are lance-shaped to oval and up to 4 centimeters long by 3 wide. The flowers are small and barely open, their tubular bases enclosed in a ribbed calyx of sepals which becomes papery and inflated as the fruits mature. The flower is less than a centimeter long and is mostly yellow in color, sometimes with brownish dots in the throat.