Senna armata – “Desert Cassia”

Also Known As: Desert Senna, Spiny senna
Other Botanical Names: Cassia armata
Family: Legume, Bean (Fabaceae)
Bloom Period: Mar-Jul
Form: Perennial Shrub
Habitat: Gravelly or sandy soil, often washes
Leaves: Pinnately-compound, drought-deciduous; alternate
Translation: “Senna” is the Latin form of an Arabic word for “thorny bush”; “armata” is Latin for “armed” which refers to the thorns; “Cassia” is Greek, derived from the Hebrew “Quelsi’oth,” meaning “fragrant shrub.”
Notes: Can appear dead for much of the year, but rain brings forth leaflets and showy blossoms, sometimes on just a few branches and other times over the whole plant. Pollinated flowers produce bright green seed pods that are upwardly-reflexed (point up), giving the plant an even spinier appearance. Leaflets are drought-deciduous, meaning they fall off at the onset of drought, but the plant’s stems are able to photosynthesize without them.
Animal Associations: Nectar source for the Cloudless Sulfur butterfly and the Sleepy Orange butterfly, both of which are well concealed among the flowers due to their coloration. Flowers must be “buzz-pollinated:” the anthers do not open and release their pollen freely, as is typical; instead, each anther has a pore at the tip, through which the pollen will emerge only when the anther is agitated, somewhat like a salt-shaker. When a bee latches on to the flower, it tips down, so the bee ends up hanging below it. Then the bee wraps its body around the anthers and vibrates its flight muscles, incidentally making a buzzing sound. The pollen comes out and is caught on tiny hairs on the bee’s underside, where it will be spread to other flowers as the bee makes its rounds. A few species of bee, for example Carpenter Bees and Bumble Bees, are the only insects capable of this feat.