Several species of “broom” were introduced into the Pacific States from the Mediterranean Area. Because these members of the Pea Family (Fabeaceae) are very invasive as well as containing toxic alkaloids that can depress the heart and nervous system of humans and livestock, the brooms are usually considered noxious weeds.
Brooms derive their common name from the Anglo-Saxon word “brom” meaning “foliage”. The word was applied to shrubs from which besoms, or bunches of twigs used as brooms, were made.
Driving along Oak Run Road (Shasta County CA) in May, Leonard and I found a large stand of French broom ( Genista monspessulana). A dark green shrub that can grow to 10 feet in height, French broom has ridged stems. The alternate, deciduous, conspicuous leaves are composed of three leaflets.
The inflorescence is 2 to 9 bright yellow, pea-like flowers in a tight cluster in the leaf axils.
French broom fruits are small legumes, hairy all over, containing brownish black seeds. The seeds are produced in abundant numbers and remain viable for many years. At maturity, the pods burst open with great force vaulting the seeds some distance away. In addition to being violently ejected from their pods, the seeds have a hard coat that permits transport through water, thereby aiding dispersal. The seeds also have a fleshy structure rich in lipids that ants readily carry back to their nests. These seed adaptations insure the aggressive spread of French broom.
Two other factors assist the survival and spread of French broom: 1) The plant loses its leaves during dry conditions, yet the photosynthetic tissue in the stems allow growth all year. 2) The roots host nitrogen-fixing bacteria allowing the establishment of French broom in nutrient-poor soils. French broom is common in disturbed areas below 1,500 feet. Although preferring full sunlight and dry, sandy soils, French broom can survive a wide variety of conditions.
Cytisus and Teline are other genera in which G monspessulana were previously placed. In Latin “brooms” were called “planta genista”, thus the current genus designation. As an aside, the Plantagenet line of English royalty took its name from “planta genista” and used the bright yellow flowers of “brooms” as their symbol. The species name is a Latinized version of Montpelier, France.
Although French broom is considered a noxious weed in the wild, I enjoy seeing the vibrant yellow flowers while driving along rural lanes.