Calochortus syntrophus is a rare species of flowering plant in the lily family known by the common names Callahan's Mariposa lily and clustered Mariposa lily. It is endemic to northern California, where it occurs in a remote area north of Montgomery Creek in Shasta County. It has also been spotted in adjacent Tehama County. Its habitat includes open, rocky areas with moist or wet soils in oak woodland territory. It was first discovered in 1993 and its description was published the following year.