Spiny senna, desert senna
The Mojave Desert (AZ, CA, NV)
Between 2 and 4 feet
Sandy locations; washes, hillsides, plains, up to 3,500 feet
Up to 6 inches long, pinnately divided into 2 to 4 pairs of short, opposite, ovate leaflets
Senna armata produces a tangled mass of grey-green branches, mixed with dead stems from previous seasons, mostly or completely leafless for the majority of the year. Stems are grooved, smooth and hairless, and the branch from the base. Leaves do form in the late winter but soon wither away, with only the thick central portion remaining. This gradually lengthens, and terminates in a weak spine.
Many flowers appear in spring, in elongated clusters from the leaf nodes at the top of the stems; flowers have five rounded, yellow (less often salmon-pink) petals, clawed (narrow) at the base. At the center is a group of ten stamens, with the anthers generally longer than the filaments. Flowers are slightly bilaterally rather than radially symmetric, since the petals are unevenly separated. Favorable late summer weather can produce a second blooming period in the fall.