California Broom-Rape (Orobanche californica)

Here’s an obscure little group of plants with which you might not be familiar. The Orobanchaceae is a family of flowering plants (dicots) consisting entirely of obligate parasites. An obligate parasite is an organism that is not capable of producing its own food because it lacks chlorophyll and is unable to undergo photosynthesis. Obligate parasitic plants are completely dependent on their hosts for nutrition. They parasitize the host plants via root-like projections called haustoria, which penetrate the stems or roots of the host plant, making contact with the water- and food-conducting tissues. An obligate parasite with which you are no doubt familiar is the bright orange dodder, or witch’s hair (Cuscuta salina var. major, family Cuscutaceae) found on pickleweed (Salicornia virginica) in Bay Area salt marshes. Some parasites co-exist harmlessly with the host plants, while others quite literally suck the “life blood” out of them, eventually causing their demise.

Contrast this with partial, or hemi-parasites, like mistletoe (Phoradendron spp., family Viscaceae), Indian paintbrush (Castilleja spp., family Scrophulariaceae), and Indian warrior (Pedicularis spp., family Scrophulariaceae). These flowering plants have green leaves and/or stems and are capable of undergoing photosynthesis. They similarly parasitize the stems or roots of their host plants, but tap only water and dissolved minerals from the host plant, not the products of photosynthesis, and cause little harm.

The broom-rape family consists of about 14 genera and 180 species, distributed mainly in temperate Eurasia and North America. It is closely aligned with the figwort family (Scrophulariaceae). California’s representatives include two genera, 13 species, and 9 subspecies, all of which are indigenous. The name broom-rape is derived from Medieval Latin for the underground turnip-like stock (rapum) of broom (Genista spp. and Cytisus spp.) Rape is the name given to the varieties of mustards (especially Brassica napus) which produce a turnip-like taproot and are grown for seeds and fodder. The seeds are used for the production of rape oil, and to a limited extent for the food of cage birds. I assume that the derivation pertains to the underground stock of the plant and the fact that it grows on the roots of other plants. The name of the genus is derived from the Greek words orobos for vetch and anchone for choke. Members of the genus cause substantial economic losses in legume crops throughout western Asia and northern Africa.

California broom-rape is a leafless, non-green plant consisting of little more than a simple or branched underground tuber-like stem attached to the roots of a host plant. In fact, the only time it is visible above ground is when it flowers, August through September. The spike-like inflorescences protrude through the soil surface two to fifteen inches. The stout, round stalk is surrounded with pale to dark purple tubular flowers one-half to two inches long on short pedicels. California broom-rape is parasitic on members of the sunflower family (Asteraceae). Near the coast Orobanche californica ssp. californica is typically associated with seaside woolly sunflower (Eriophyllum staechadifolium) and gumplant (Grindelia spp.) Elsewhere, other subspecies are parasitic on such plants as sagebrush (Artemisia tridentata), coyote bush (Baccharis pilularis), fleabane daisy (Erigeron spp.), and aster (Aster spp.)

The type specimen of California broom-rape was collected by Chamisso in San Francisco in 1816. In San Francisco, it is known historically from coastal bluffs and sandy hills at Land’s End (1923), Ingleside (1920), and the sand dunes (1914). Unfortunately, it has not been reported from San Francisco in recent years. California broom-rape inhabits sandy or heavy soils. On the northern San Francisco Peninsula, it is extant on San Bruno Mountain, Mori Point in Pacifica, and elsewhere. California broom-rape reaches its northern limits along the Mendocino County coastline, extending southward through Sonoma, Marin, San Mateo, Monterey, San Luis Obispo, and Santa Barbara counties.

The underground stems of Orobanche are indeed edible. In Tunisia, for example, the floral stem is removed at a point beneath the flower. Being starchy, it is dried, ground into flour, and then mixed with barley flour. The Chambaa and the Touareg tribes of North Africa eat the plant raw or boiled, where it is used as a diuretic. I call broom-rape a lunch plant, not because it is edible, but because one usually comes across them only accidentally when sitting on the ground for a lunch break. So next time you’re out hiking the coastal hills in late summer, stop for lunch near a clump of seaside woolly sunflower. Maybe you’ll come across this oddity. And be sure to let us know if you find it in the city!