Caulanthus cooperi is a species of flowering plant in the mustard family known by the common name Cooper's wild cabbage. It is native to the southwestern United States and Baja California, where it is a common plant in a number of open, sandy habitats. This annual herb produces a slender, somewhat twisted stem with widely lance-shaped to oblong leaves clasping it. The flower has a rounded or urn-shaped coat of pinkish or pale greenish sepals enclosing light yellow or pale purple petals. The fruit is a straight or curving silique several centimeters long.