GROWTH HABIT: Gray horsebrush or spineless horsebrush is a perennial, deciduous shrub growing from ½ to 3 feet tall.
LEAVES: Leaves are simple, alternate, linear and wooly with a prominent midrib.
STEMS: Stems are short, stout and silvery canescent until maturity then become glabrous; nodes are prominent causing a "knobby" appearance.
FLOWER: Flowers are borne in terminal clusters and are yellow to cream-colored.
OTHER: Gray horsebrush is a native rangeland plant and is common throughout rangelands of the West. It causes photosensitization in sheep, an allergic reaction of the skin caused by exposure to sunlight, symptoms of which are called "big head" from swelling of the head and facial features. Horsebrush causes severe liver damage when large amounts are eaten, and sheep may die within a day or two, while small amounts cause various degrees of photosensitivity to develop. Control measures for horsebrush have not been successful.