French broom has few peers as a villainous invader. A single plant can produce 10,000 seeds per season, and it spreads them via sticky, hairy pods that attach to moving animals as well as many other carriers. The pods then explode, scattering seeds as much as 13 feet in all directions. The seeds can remain dormant in soil for more than five years. If unchecked, the plant forms dense thickets where nothing else will grow. Its branches interweave so tightly that neither wild nor domestic animals can penetrate. It will shade out tree seedlings in newly forested areas. Once firmly established in dry conditions, it easily catches fire, carrying flames to the tree canopy if present; it then regrows from the ashes more abundantly. Its stands may expand more than ten feet in a year. Its leaves and seeds contain alkaloids that are poisonous to domestic livestock other than goats.
A native of the Mediterranean, French Broom was brought to the Bay Area in the 1800s as an ornamental. It soon escaped, and attracted attention as a weedy invader as early as 1925. The California Department of Transportation planted it extensively along highways until the late 1970s. Today French broom is listed as a severe noxious weed in California and all other Western states with a similar climate. Park stewards in Marin County and elsewhere, with the help of thousands of volunteers, have waged legendary, epic battles to remove it. There are still an estimated 100,000 acres of French broom growing in California.
Park staff and anonymous volunteers have kept a sharp eye out for French broom in Cesar Chavez Park for several years, and pulled it up wherever it happened to sprout. The specimen shown in the photo above, growing on the north side of the park, is no longer a threat. Chavez Park Conservancy volunteers pulled it up in early May. The plant came up with its entire tap root, two feet long. A smaller French broom growing near the northeast corner met the same fate. As of this date, no French broom plants are known to be growing in the park.