OF THE WEEK
Dr. T. Ombrello - UCC Biology Department
Common names: Dodder, Love Vine, Knot Weed, Strangleweed, Stranglevine, Angelís Hair, Devilís-Guts, Goldthread, Pull-Down, Devilís Ringlet, Hellbind, Hairweed, Devilís Hair, Hailweed, Tangle Gut, and Witches Shoelaces.
Scientific name: Cuscuta spp.
Explanation of scientific name:
Cuscuta Ė The origin of this Arabic-based name is unknown.
|Dodder growing on a Salvia plant.|
growing on an Impatiens plant.
|Dodder growing on
Petunias and Crabgrass.
When most folks think of plants, and especially flowering plants (Angiosperms), they envision sedentary life forms capturing the sunís energy by way of photosynthesis in leaves filled with the green pigment chlorophyll. Almost all plants make their own food by this process, and synthesize all the macromolecules they need. They represent the largest group of autotrophic organisms on Earth. But, there are some notable exceptions to this generally held view of plant life, and Dodder is certainly one of the most interesting examples. Imagine a plant without leaves or roots, a plant consisting of yellow/orange stems that twine around and draw the life sustaining sap out of nearby green plants. Thatís Dodder!
Dodder is one of many often amusing and imaginative common names for the members of the genus Cuscuta (see above). These Morning Glory relatives are found around the world, and are represented by 170 very similar species. Some, like those found in NJ, are annuals. They grow each summer from seeds produced in previous years. The perennial types are found in tropical regions. These grow for many years, parasitizing shrubs and trees. I have seen a single Dodder plant cover the entire canopy of a sizable tree on the Caribbean island of St. Martin.
The orange/yellow Dodder vines are covering the trees and shrubs in this area on Peter Island of the British Virgin Islands.
The life history of Dodder plants is fascinating. In NJ, Dodder seeds germinate in the spring. The resulting plants are obligate parasites in that they must find a suitable host within a few days. If they donít, they die when the stored food in the seed is exhausted. Dodder seedlings find a host by waving their rapidly elongating stems in a clockwise fashion, hoping to contact a potential host. This motion is so slow that it requires time-lapse photography or careful observations over many hours to be perceptible. When contact is made with a solid object, the stem tightly twines around it. If the host is one that meets the needs of that Dodder (the various species have specific host preferences), modified adventitious roots called haustoria will grow from the stem, and slowly penetrate the host. The haustoria push and enzymatically digest their way in. A vascular connection develops soon thereafter, and essentially all the nutrients the Dodder plant needs are drawn from the host. Dodder does produce a bit of chlorophyll for photosynthesis in its buds, fruits, and stems. But the minimal quantity of it contributes a negligible amount to the nutrient requirements of the plant. After the vascular connection is completed, the lower portion of the Dodder stem dies, and all contact with the soil ends. The Dodder plant can move from plant to plant in its quest for resources. A thriving infestation is a tangled, clinging mass that looks as if someone has draped cooked spaghetti over the host plants. Rarely does the host plant die, but it does lose vigor and appears unhealthy.
From mid-summer through the fall, Dodder plants in NJ produce clusters of small white/yellow flowers less than 1/8 inch across. After pollination, 1/8-inch fruits develop, each containing 1-4 seeds. The seeds are dispersed by a variety of means, including but not limited to irrigation water, agricultural equipment, shoes, topsoil that is moved, and even through the digestive systems of mammals and birds. The seeds do not all germinate the following year. Some remain dormant for up to 5 years or more, insuring that Dodder may grow on the site even if the previous year could not support its growth. Dodder seeds in the ground seem to delay their germination if a suitable host plant is not growing nearby.
Dodder can be a noxious weed. It is included in the US Department of Agricultureís list of the 10 most problematic weeds in our country. It has earned that status because of its persistence as described above, and the fact that it is very difficult to eradicate once it becomes established in an area. Herbicides that could kill it will also kill the host plant it is growing on. Dodder is a serious pest on wild and cultivated plants including alfalfa, flax, clover, potato, blueberry, chrysanthemum, dahlia, petunia, salvia, coleus, and geranium. When alfalfa, clover, and onions are grown for seed, Dodder is especially problematic because its seeds are not easily separated from the crop seeds, and the contamination can result in the seed crop being unmarketable. Some plants, such as cereal grains, corn, and soybeans, will not support Dodder parasitism, and are rarely troubled by it. If its parasitic nature was not enough of a problem, Dodder can also be the vector of plant diseases. Dodder can pick up systemic diseases, to which it is immune, from host plants and pass them along to other host plants it encounters. Yellows, pear decline, and elm phloem necrosis are a few of the diseases known to be spread by Dodder.
Dodder appears regularly in our area. I find it growing just about every year on Union County Collegeís Cranford campus. If you find it on plants around your home it would be prudent to destroy it immediately. It is a weed in no danger of extinction that has the potential to be a gardenerís nightmare.