Mentzelia affinis is a species of flowering plants in the family Loasaceae known by the common name yellowcomet. It is native to the southern half of California, Arizona, and adjacent sections of Nevada and Baja California, where it is known from scrub, woodland, desert sands, and other habitat types. It is an annual herb growing erect to maximum heights anywhere between 5 centimeters and half a meter. The leaves are up to 17 centimeters long in the basal rosette, divided into lobes and sometimes toothed, and smaller farther up on the plant. It is an annual herb growing erect to maximum heights anywhere between 5 centimeters and half a meter. The leaves are up to 17 centimeters long in the basal rosette, divided into lobes and sometimes toothed, and smaller farther up on the plant. The flower has five shiny yellow petals, each with an orange spot at the base and often a toothed or notched tip. The fruit is a narrow, curving utricle 1 to 3 centimeters long. It contains many tiny prism-shaped seeds.