California Dodder

A field smothered in dodder looks like it has been attacked by Silly String.⁵⁶

Dodder species are leafless orange parasites. Fortunately, the three species of dodder in the Reserve are native species that have evolved with and adapted to their host species. Like any good parasite, California dodder rarely kills its host.

In summer, large patches of orange-brown California dodder may be seen covering buckwheat, black sage or deer weed in the coastal sage scrub, while other native dodder species are found in the salt marsh and brackish marsh parasitizing different species.

Description ^2,3,4,11,59

California dodder is a parasitic, herbaceous annual plant that resembles fine strands of orange-brown spaghetti strewn across and within species in the coastal sage scrub. As a parasite, it lacks a root with which to take up water and nutrients from the soil, and chlorophyll with which to turn light and carbon dioxide into carbohydrates. The mature dodder plant obtains all of its food and water from the “host” plant. Several host species have been reported for California dodder, including California buckwheat (Eriogonum fasciculatum), California croton (Croton californicus), sand aster (Corethrogyne filaginifolia),  species of sage (Salvia spp.), and a variety of herbs, including annuals.⁵⁹ In the Reserve, parasitism by California dodder is largely restricted to three species: California buckwheat, deer weed (Acimspon glaber) and black sage (Salvia mellifera).

Leaves are short-lived, scale-like structures that are rarely seen. Flowers, however, are attractive, if somewhat less than showy. Flowers are small, about ¼ inch across (.65 cm). They are radially symmetrical with five narrowly pointed petals united at the base into a shallow tube above which they flare outward, often bending backward with age. Five sepals are united into a tube that encloses the flower base. Flowers are bisexual. Five anthers extend beyond the petals. The pistil has two filamentous styles each topped with a small, spherical stigma. The main flowering period is May – August.¹

The fruit is a pin-head-sized capsule containing two to four seeds. The capsule is subtended by the calyx and may be surrounded by persistent dead petals.

Classification ^2,7

California dodder is a dicot angiosperm usually placed in the morning glory family (Convolvulaceae), but occasionally in its own family (Cuscutaceae). Members of the morning glory family are characterized by a twining or trailing habit and by their five-lobed, funnel shaped flowers.⁴⁴ The sweet potato is a morning glory, as is the weedy and troublesome bindweed. Dodder is the only parasitic genus in this family.

In the Reserve, we have three species of dodder. In addition to, C. californica, we have C. pacifica and C. salina that grow on plants of the salt marsh and alkali flats. Elsewhere in the state, however, non-native species have been introduced and have become serious agricultural pests.^56,97

There are three varieties of California dodder currently recognized in California.² The variety that has been described from the Reserve is var. californica.⁴⁸

Ecology

In spite of the fact that California dodder spends most of its life with no contact with soil, it reproduces by means of a normal, rooted seed. The seed contains enough carbohydrates to support the seedling’s growth for 5-10 days. During that time, if the dodder is to survive, it must reach and attach to a suitable host. Since not all plants are suitable and hosts may be widely spaced, it seems unlikely that the dodder depends on random chance. In fact, in 2006, three researchers demonstrated that a dodder seedling can “smell” its host.^98,99 All plants emit volatile organic compounds. Some, such as the pungent aroma of sagebrush, are readily detected by humans. In the case of dodder, the volatile compounds produced by a host plant direct a seedling to the host, whereupon it penetrates the host tissue with small root-like structures called haustoria, and the original root dies. At that point, the dodder becomes dependent upon the host for all its water, mineral and carbohydrate needs.

One dodder plant can completely engulf its host plant. In fact, a single dodder can infect more than one host at the same time. In spite of this, it is unusual for the native dodder to kill its native host.⁴¹ California dodder is an annual plant. In the Reserve, the hosts are perennial. If the host survives the months of infestation, the parasitic dodder will die and the host has a recovery period. Only if a host is unlucky enough to be infected several years in a row, is it likely to die entirely. Thus the native dodder and their native hosts have reached a balance that assures persistence of the host species and hence a continuing supply of hosts for the dodder.

Human Uses

Dodder growing on buckwheat (and only buckwheat) was used by Kumeyaay as a cure for black widow spider bites.^18,101

A natural yellow dye may be made by boiling dodder and fixing it with a mordant such as alum.¹⁰²

Interesting Facts

Dodder species have been given an assortment of fanciful names: witch’s hair, love-vine, strangle-weed, devil’s hair, golden thread,²³ devils sewing thread,⁹⁹ hell-bind.³⁹

Unfortunately, species of non-native dodder (especially Japanese dodder in California) have become serious agricultural pests,¹⁴⁴ and many species of dodder are listed on the federal noxious weeds list of the U.S. Department of Agriculture.^56.