The Sonoran Desert Florilegium

plants of the florilegium

Senna covesii
Desert senna

FAMILY:  Fabaceae — Legume family

SYNONYMS:  Cassia covesii

ETYMOLOGY:  The name of the genus Senna is taken from the Arabic sana, a word used for cassia plants in general (Senna covesii at one time was classified as Cassia covesii).

The species name covesii honors Elliot Coues (1842-1899), a noted ornithologist and surgeon in the Union Army. His name is Latinized in the epithet, with 'v' replacing the original 'u'.

DESCRIPTION:  The perennial desert senna blooms from April through October. The 1" mustard yellow flowers contrast nicely with its silver gray-green leaves.

The desert senna does not provide nectar for its pollinators, only pollen. Carpenter bees and bumble bees use a special technique called buzz pollination for harvesting pollen. Instead of splitting open lengthwise to release pollen, the plant's anthers have a small pore at the top. The bee wraps its body around the anther and vibrates its flight muscles. The pollen comes out the anther pore, landing on the body of the bee. The bee will then transfer the pollen to other plants.

The stems of the desert senna become woody with age. After pollination, seed pods develop and eventually dry to a light brown color. The pod remains on the plant for a long time after it splits and releases the seeds.

Desert senna occurs on dry rocky slopes and mesas at elevations between 1,000-3,000'.