General: Longspine Horsebrush (Tetradymia axillaris) is an upright, spiny shrub growing 3- to 4-feet tall with often leafless, bright white stems. The stems are evenly covered in dense, matted, silvery hairs (tomentose). The leaves are in two forms: main leaves and clustered leaves. Main leaves are green and tomentose, but they look like long, thick spines. These leaves lose the hair and dry to become long, thin spines without hairs (glabrous). Clustered leaves look like regular leaves, but they are small, linear, fleshy, glabrous, and of course, occur in tight clusters.

During spring and early summer, one or two yellow flowerheads are produced in leaf axils. Each flowerhead is composed of several disk flowers, but no ray flowers. Each flower produces many hairs that, when the entire plant is ripe, look like cotton or cotton balls stuck among the spiny twigs.

Longspine Horsebrush is a fairly common component of shrub communities on well-drained sandy, gravelly, and rocky soils on upper bajadas and moderate slopes into the lower mountains in the Upper Sonoran (Mojave Desert Scrub and Pinyon-Juniper Woodland) life zone.

Family: Sunflower (Asteraceae).

Other Names: Cottonthorn, Horsebrush, Tetradymia

Plant Form: Upright, drought deciduous shrub.

Height: To about 4 feet.

Bark: Silvery white (bright white due to tomentose hairs).

Stems: Evenly tomentose. Stems tend to grow straight upright with straight, 1-inch main leaves (spines to be) that grow perpendicular to the stems. Spines hairless and more-or-less straight in age.

Leaves: Two kinds of leaves: main and clustered. Main leaves (20-50 mm) grow on new stems and form the spines. Clustered leaves (2-12 mm) grow in axils. Clustered leaves are alternate, oblanceolate, green, and hairless.

Flowers: Blooms spring through summer. Inflorescence: flowerheads with up to 7 disk flowers, yellow.

Seeds: Fruits hairy. Tiny achene (like a tiny sunflower seed) with many fine bristles.

Habitat: Dry, well-drained sandy, gravelly, and rocky soils on upper bajadas and moderate slopes in the lower mountains.

Elevation: About 3,000 to 4,500 feet.

Distribution: Southern California deserts and southern Nevada, plus extreme SW corner of Utah and NW corner of Arizona.

Comments: There are two varieties: T. a. axillaris with flowerheads glabrous and T. a. longispina with flowerheads tomentose.