Psorothamnus arborescens (Torr. ex A.Gray) Barneby

Taxonomic Classification

This species, currently classified as Psorothamnus arborescens, was previously named Psorodendron arborescens.

Growth Form and Stems

It is a shrub that grows no taller than 1 metre (3.3 ft), with highly branching stems that sometimes bear thorns.

Leaf Characteristics

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.

Inflorescence Structure

The inflorescence is a long raceme holding many flowers.

Flower Features

These flowers have reddish green calyces made of sepals, and bright purple pealike corollas that reach up to 1 centimeter in length.

Fruit Characteristics

The fruit is a glandular legume pod, which grows up to 1 centimeter long and holds a single seed.

Species Distinguishing Trait

This seed pod is the only feature that can distinguish P. arborescens from the very similar related species P. fremontii.

Native Distribution and Habitat Types

Psorodendron arborescens is native to southwestern North America, where it occurs in many types of desert and dry mountainous habitats.

Elevation Range

It grows at elevations between 100 metres (330 ft) and 1,900 metres (6,230 ft).

Geographic Range Details

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.

Additional Distribution Locations

It is also found in northwest Arizona's Joshua Tree National Forest.