Spiny Senna

The scientific name for Spiny Senna (Senna armata) hints at its defensive nature, with "armata" suggesting arms or armor. True to its name, the Spiny Senna is armed with soft spines that bend to the touch. Another common name for this plant is Desert Senna. It is native to desert regions around the intersection of Nevada, Arizona, eastern California, and northern Baja California, where it thrives in sandy and rocky habitats such as dry washes. You’ll often find it growing alongside Creosote Bush, Cheese Bush, and various cacti in desert scrub areas.

This shrub typically grows to about 3 feet tall, with grooved, branching stems that often narrow into thorn-like tips. Its spiny branches are covered in fine hairs, which protect the plant from the hot desert air. The spine-tipped leaves consist of two to four pairs of small leaflets. These leaves are ephemeral, meaning they drop off soon after emerging, leaving the shrub leafless for much of the year.

From April to May, Senna armata produces small clusters of fragrant, showy yellow to orange flowers. These plants are an important food source for the Cloudless Sulfur and Sleepy Orange butterflies.

As a member of the pea or legume family, Senna armata is a nitrogen-fixing plant. It forms a symbiotic relationship with soil bacteria that live in nodules on its roots. These bacteria convert atmospheric nitrogen into a form that the plant can use, in exchange for sugars and a suitable environment provided by the plant. When the plant dies, the fixed nitrogen is released back into the soil, enriching it for other plants.