Cuscuta and Grammica
by Cheryl Miller
Ever seen this type of tangled mess on a desert tree, on the ground or over a shrub? This unattractive
clutter is actually a freeloading plant called Dodder, the common name for over 150 worldwide species
of the new Custcutaceae Family, previously part of the Morning Glory Family or Convolvulaceaes.
There are at least 20 species of Dodder growing on the Baja Peninsula with so minute differences, and so little research done on this registered invasive weed, that a singular discussion of each would yield little. So, we will discuss Dodder with its two botanical genera called Cuscuta and Grammica (distinctions made due to the stigma shape only), in general, as Dodder.
Dodder is a true parasite that, unlike mistletoe and other species of parasitic plants derives not only water and minerals from their host, but also their carbohydrates (food) through a process called haustoria. Dodder has little-to-no chlorophyll itself, so it is physically unable to photosynthesize which plants use to produce the carbohydrates necessary for life. Dodder therefore, depends entirely on the sustenance of the mother plant for all of its nutrients. A true “blood sucker”. In fact, although this plant reproduces from seeds that sprout in the earth, once established on a host plant, they readily lose their rooted connections in the soil, which whither, die and break off. Interesting, somewhat like an umbilical cord!
Dodder plants universally send out fine vines with clinging tendrils that wrap and secure themselves onto the surfaces of their host plant. The clinging tendrils always wrap in a counter-clockwise direction. At this point, the plant sends out leaf-like shoots that affix themselves to the host whereupon an enzyme chemical is secreted which breaks down the bark or outer sheath of the host plant, allowing the Dodder to literally suck the life juices out. Fascinatingly, this parasite rarely kills the host plant, no matter who infested it may be. But, Dodder causes Phtyoplasma, a cause of over 200 possible “yellow” diseases that do affect the quality of life of its host and often retards the size and growth of its host. In addition, should the host plant have any virus present in its system, the added burden of the Dodder weakens its resistance and can cause the disease to flourish. And in desert conditions where water is limited, significant damage to its host may occur.
The vines and tendrils, in Baja California species are most often yellow to cream color and very fine However, one species the Cuscuta gigantea, tend to be more green and are, as its name implies, “giant”, with diameters of up to ¼ of an inch. In Europe and some parts of the U.S., vines can be found in shades of orange, pink and red. So profuse is its growth, that the vines often overtake its host, blocking sunlight to leaves and earning itself names such as “devil’s guts”, “devil’s hair”, “devils ringlet”, “goldenthread”, “hairweed”, “strangleweed” “witches shoelaces” and “witch’s hair”. Vines grow so quickly, some as much as 4-5 inches a day, that is not unusual to find the vine at the top of trees, or over multiple trees and bushes.
On some species small, minute true leaves may occur, others produce only the leaf-type structures that affix themselves to the plant. Dodder flowers are also very miniscule ranging in color from white to pink to yellow to cream, but produced in vast quantities on each plant. Flowering periods are species dependant, but most bloom in early summer and produce seeds that have a hard coating that can survive in the soil for 5 to 10 years or more. The profuse production of these seeds almost insures that the host plant and its surroundings will see another visit from the Dodder the following year!
The Dodder, researchers have determined, uses airborne chemical clues to “sniff” out their hosts. This vampire actually smells its victim and grows towards it. In trials, wafted odors of a tomato plant and a wheat plant were directed toward seedlings. A chemical in wheat repelled the seedlings, while they visually turned and grew towards the tomato plant. Since the Dodder seedlings have less than 10 days to find and secure itself onto a host before it will die, this little animal-like behavior ensures its survival. But perhaps, the chemical in wheat can be used as a repellent in the future?
As Dodder species are host-specific, many of the specie distinctions originate in these preferences. For example, C. approximata, common from British Columbia to Baja California and east to the Dakotas, attacks alfalfa farms and becomes a serious problem. Since seed and plant products need to be tested for the
presence of the Dodder seed (among other weeds), an infestation can cripple the sellable yield of a farmers crop. Throughout the world, Dodder is considered an invasive weed. As a result many countries prohibited from importation of Dodder, its seed or its by-products; and are employing eradication techniques such as pre-emergent seed herbicides, removal of host plants and not replanting them for several years, planting immune crops such as soybean, and removal of the Dodder itself, especially before flowering or seed setting. However, some experts say (tongue in cheek) the only sure way to eradicate Dodder is with a flame thrower! In California, experts thought they had completely eradicated the C. reflexa for many years, only to find it remerge in a different county recently.
The only indigenous uses for this plant, documented and found, was in Brazil and England, none have been documented here in Mexico.
If you find this interesting, but harmful plant in your garden, don’t just stand there and gawk…get rid of it ASAP!