Saltmarsh Dodder (Cuscuta salina var. major)

Beginning in May, as you drive past the salt marshes rimming San Francisco Bay, you might begin to notice an orange hue starting to spread over the tops of pickleweed plants. On closer inspection, you’ll see what looks like orange threads forming a net over the shrubs. Over the course of the summer, this brightly colored netting can completely obscure its hosts, looking like some kind of alien invasion. But this is no alien. It’s saltmarsh dodder (Cuscuta salina var. major), a home-grown curiosity, indigenous here, and doing what comes naturally.

Known by such folksy names as devil’s guts, devil’s hair, devil’s ringlet, hailweed, hairweed, hellbine, love vine, pull-down, strangleweed, strangle gut, tangle gut, witch’s hair, witch’s shoelaces, and goldenthread, all dodders are parasites that capitalize on the photosynthetic abilities of their host plants. Although germinating seedlings of Cuscuta produce tiny roots, the stems quickly attach to host plants and break off their terrestrial connection. In fact, if seedlings do not come into contact with a host plant within about ten days, they will exhaust their food stores and perish. From aerial stems, dodder produces haustoria, rootlike structures that penetrate the cell walls of green plants (but without penetrating the protoplast of the cell), absorbing the nutrients and water they need for growth. Similar structures are found in fungi, functioning in the same way. Although lacking much visible green in their stems, most species of dodder do contain low levels of chlorophyll. In temperate regions, dodder is typically regarded as an annual, although in mild climates such as ours haustoria can overwinter, sprouting again in the spring. Looking more like the hair for a Halloween costume, you’d be forgiven if you were uncertain in which Kingdom dodder falls. But it is indeed a flowering dicotoledonous plant (Division Anthophyta, Class Magnoliopsida).

Until recently, dodder was placed in its own family, Cuscutaceae. But taxonomists have recently determined that the basis for this determination, its parasitic nature, was not sufficient grounds for separating it from the morning-glory family (Convolvulaceae), the family to which it once again belongs. Worldwide, there are about 170 species of Cuscuta, all of which are parasitic. Numerous species of dodder are regarded as highly invasive, problematic pests on a variety of hosts. Largeseed dodder (C. indecora) and field dodder (C. campestris) are major pests in the western United States, infesting alfalfa and clover crops. Although not present in California, fortunately, giant dodder (C. reflexa) is a serious pest of citrus, coffee, peach, and forest trees. However, especially dense infestations can physically reduce the light reaching host leaves as well as weaken the host plant’s natural resistance to diseases. Dodder can also spread viruses between plants. Some species of dodder, most notably Japanese dodder (C. japonica), are used in Asian medicines as a male aphrodisiac; a liver, kidney and digestive tonic; and for “female reproductive problems.” Most infestations of non-native dodder are reportedly associated with Asian immigrant communities, as the seeds are imported with the herb treatments (Markmann 2006). In fact, the planting of this species by Hmong immigrants as a home-grown source of these traditional medicines has alarmed state officials, who are actively working with members of that community to educate them about the environmental hazards posed by its spread.

California’s native dodders grow on a variety of herbaceous and shrubby species and, when confined to natural plant communities, they are not considered invasive or particularly problematic. However, because dodder has the potential to become invasive, the federal government considers all Cuscuta species as noxious weeds.

California supports 11 native species, nine varieties, and two naturalized non-native species of dodder. Native species of dodder occur in chaparral, grasslands, yellow pine forests, creosote bush scrub, and salt marshes. Some of the host plants on which dodder can be found include Ambrosia, Artemisia, Asclepias, Aster, Ceanothus, Cressa, Eriogonum, Eryngium, Haplopappus, Hymenoclea, Larrea, Medicago, Polygonum, Prunus, Quercus, Rhus, Salicornia, Salix, Suaeda, Trifolium, Xanthium, and many members of the sunflower (Asteraceae), legume (Fabaceae) and goosefoot (Chenopodiaceae) families.

Saltmarsh dodder produces twining, yellowish-green to bright orange stems. The stems are fragile and easily broken into segments when handled. The leaves, inconspicuous and nonfunctioning, at least in the traditional sense, are reduced to small scales arranged alternately on the stems. Flowers are produced in small clusters along the length of the vining stems. The flowers themselves are about 1/4 inch wide, consisting of five, white, almost translucent petals. Fruits are small, white, berry-like capsules producing a single seed surrounded by the whithered corolla. In our area, saltmarsh dodder blooms from May through September.

Saltmarsh dodder occurs at low elevations and in saline locales from the Mexican border to British Columbia. The range of the genus extends eastward to Utah and Arizona. The primary host plants of saltmarsh dodder are the pickleweeds (Salicornia spp.), alkali weed (Cressa truxillensis), and seablite (Suaeda spp.), although our local variety (C.s. var. major) occurs mostly on pickleweed. Locally, it has been reported “attacking” the invasive glasswort (Salsola soda) and may have contributed to its eradication at Piers 94 and 98.

No California dodders are considered rare or endangered, and none is regarded as being at risk of extinction by the California Native Plant Society. Here in San Francisco, saltmarsh dodder is considered locally significant due to its very restricted distribution in the county. This is, of course, merely the result of the limited amount of saltmarsh habitat found within our area. In their A Flora of San Francisco, California, Howell, Raven, and Rubtzoff (1958) report records for saltmarsh dodder from the Presidio, near Islais Creek, near Hunter’s Point, and in Vistacion Valley. Within the county limits, you can still find it in the Presidio, at India Basin, and at Heron’s Head Park (Pier 98).

So during your summer wanderings around the Bay’s edge, while bird watching or enjoying the magic of a summer fog bank pouring over the coastal hills, you might want to take witness to that rapidly spreading orange netting as it creeps over the pickleweed. Look for the flowers. See which birds collect the tiny white fruits; harvesting by birds has not yet been documented. And when you see the orange mats, don’t worry. It’s not yet another scourge wrought by humans upon the natural world. This one was here long before we showed up.

REFERENCE:

Markmann, C. 2006. Summary of Dodder (Cuscuta japonica) Biology, Concerns, and Management. Revised and augmented by R. Marushia. July 21. California Department of Fish and Game.

http://www.aquariumofpacific.org/onlinelearningcenter/species/saltmarsh_dodder

Posted in Focus on Rarities.

Michael Wood

President, Wood Biological Consulting, Inc.
Wood Biological Consulting, Inc. San Francisco State University