About Psorothamnus arborescens (Torr. ex A.Gray) Barneby
This species, currently classified as Psorothamnus arborescens, was previously named Psorodendron arborescens. It is a shrub that grows no taller than 1 metre (3.3 ft), with highly branching stems that sometimes bear thorns. Its leaves are each composed of a few pairs of green leaflets that range in shape from linear to oval, and grow up to 1 centimeter in length. The inflorescence is a long raceme holding many flowers. These flowers have reddish green calyces made of sepals, and bright purple pealike corollas that reach up to 1 centimeter in length. The fruit is a glandular legume pod, which grows up to 1 centimeter long and holds a single seed. This seed pod is the only feature that can distinguish P. arborescens from the very similar related species P. fremontii. Psorodendron arborescens is native to southwestern North America, where it occurs in many types of desert and dry mountainous habitats. It grows at elevations between 100 metres (330 ft) and 1,900 metres (6,230 ft). Its range includes the Californian Mojave Desert and Colorado Desert, extending south into the Sonoran Desert in the Mexican state of Sonora, east past the Sierra Nevada into Nevada's Great Basin Desert, and west into the San Bernardino Mountains of Southern California. It is also found in northwest Arizona's Joshua Tree National Forest.
