In late October when Leonard and I visited the Oregon and California Coasts, we were surprised at the number of wildflowers still in bloom. Cutleaf beach bur (Ambrosia chamissonis) was one of these late flowers at Chrissy Field State Park (Oregon).
A type of ragweed, cutleaf beach bur is found along the Pacific Coast from Alaska to Baja and also in western South America below 100 feet. Its habitat is coastal dunes and sandy or gravelly beaches.
This native perennial, which smells sweet, arises from a taproot and forms large clumps. The stems are branched at the base, spreading, leafy, hairy and longitudinally ridged. Cutleaf beach bur leaves are mostly alternate and generally hairy. The leaves have stalks. The blades may be toothed or deeply divided.
A member of Asteraceae, cutleaf beach burs have both male and female flowers on the same plant, arranged in leafless terminal spikes. The staminate (male) flowers are at the end of the spike while the pistillate flowers are clustered below them. Between 25 and 50 yellow-greenish, staminate flowers are arranged in a head. The single pistillate flowers have several rows of spiny involucral bracts.
Cutleaf beach bur fruits are achenes (single dry seed) enclosed within the bracts with the whole forming a bur covered in spines with hooks or teeth. Unlike many members of the Aster Family, the seeds have no pappus.
Silver beach bur and silver burweed are other common names for A chamissonis. A synonym for A chamissonis is Franseria chamissonis. The species designation honors Adelbert von Chamisso (1781 – 1838), a French-born German botanist who botanized in the San Francisco area with J.L. Eschescholtz. Ambrosia in mythology was the food of the gods and rendered life immortal. People believed that eating sweet-smelling plants gave the long life, thus the genus name.