|Desert Senna (Senna covesii)|
DESCRIPTION: Perennial to 2'. Flowers pale yellow with 5 petals to 1" wide. Fruit a woody, brown pod that splits down the middle and persists on the plant. Leaves simple pinnately compound, usually with 3 pairs of leaflets per leaf. Leaves grayish-green with fine hairs. Fabaceae (Legume) Family.
NATURAL HISTORY: Flowers bloom in spring and fall. Flowers are buzz-pollinated. When Carpenter Bees and bumblebees come to the flowers, they vibrate their wing muscles, creating a relatively loud buzzing sound(compared to the buzz of flight). This high intensity vibration shakes pollen out of the anthers and onto the bees. Carpenter Bees have special hairs that "catch" the pollen, and then the bees transport the pollen to other desert sennas for pollination. For your information, tomatoes are buzz-pollinated too (electric toothbrushes are used in greenhouses without bees).