Dodders are parasitic plants that usually look like a hairlike mass of yellow or orange, seemingly leafless, wiry, vining stems wrapping around the stems of other plants. At first, you might not think they are plants at all.
Dodders are parasitic on the aboveground portions of plants. In Missouri, they are nonwoody annual vines. Dodder stems are hairless, twining, and often form tangled mats. They may be greenish yellow, yellow, or orange. They attach to the tissues of host plants by suckerlike structures called haustoria.
The leaves are not very apparent. They are very small, about 1/8 inch long, alternate, stalkless, usually resembling scales. Leaf shape varies with species.
The bell-shaped flowers are small and in clusters. They may be smooth or they may have warty or bumpy textures. The calyxes (joined sepals) are 3–5 lobed, sometimes divided deeply enough to be separate sepals. Petals are white or greenish. The 2-celled ovary has 2 styles. Our species bloom June or July through September or October.
The fruits are papery-walled, 2-celled capsules, usually with a slight space between the 2 stigmas. The capsules of Missouri species break open irregularly. Seeds usually 2–4 per fruit, brown. A single plant can produce thousands of tough-coated seeds.
Most dodders parasitize a wide variety of host species, and identifying the host species is usually not an aid in identifying the various dodder species.
Missouri has 10 dodder species. To separate them, you must use a hand lens to carefully examine tiny details of the flowers, such as how deeply divided the calyces are; whether the flowers are on stalks or are sessile; whether the surface of the flowers is bumpy or smooth; the number of lobes on the calyces and corollas; the shape of the calyx and corolla lobes; and so on.
- Field dodder (Cuscuta campestris). Scattered statewide, mostly in moist habitats but also along field edges and other disturbed habitats. Parasitizes a wide variety of mostly nonwoody plants.
- Buttonbush dodder (C. cephalanthi). Scattered nearly statewide, on stream banks, bottomland forests, and wet prairies. Parasitizes both woody and nonwoody plants.
- Compact dodder (C. compacta). Scattered, mostly in the southeastern quarter of the state, in bottomland forests, swamps, and banks of streams and sinkhole ponds. Parasitizes both woody and nonwoody plants.
- Hazel dodder (C. coryli). Relatively uncommon and widely scattered, on stream banks, bottomland forests, and prairies. Parasitizes both woody and nonwoody plants.
- Cusp dodder (C. cuspidata). Scattered in the southern half of the state, mostly on banks of rivers, streams and ponds, but also in wet prairies and sometimes as a weed in fields. Parasitizes a wide variety of nonwoody plants.
- Rope dodder (C. glomerata). Scattered, in a variety of habitats, including wet and dry prairies, various forest types, fens, and roadsides. Parasitizes a wide variety of nonwoody plants.
- Common dodder (C. gronovii). This is one of the most common species of dodder in the state. Scattered to common statewide, except in the northernmost counties, in bottomland forests, swamps, fens, gravel bars, banks of streams, and along the margins of ponds, lakes, and sinkhole ponds. Also sometimes found along railroad tracks, as a weed in fields, and in other disturbed habitats. Parasitizes a wide variety of woody and nonwoody plants.
- Large alfalfa dodder, or pretty dodder (C. indecora). Introduced along railroad tracks in St. Louis city, but apparently also native to the state, based on historical collections in Barry, Franklin, and McDonald counties, where it was said to grow on low ground or rocky areas. Parasitizes a wide variety of usually nonwoody plants.
- Field dodder, or five-angled dodder (C. pentagona). This is one of the most common species of dodder in the state, and it is probably the most commonly encountered dodder in prairies and glades. Scattered statewide on stream banks, swamps, and a variety of dry and wet prairie, glade, and forest types. Also frequently a weed in fields and along railroads. Parasitizes a wide variety of woody and nonwoody plants.
- Smartweed dodder (C. polygonorum). Scattered statewide, along streams and ponds and in swamps, bottomland forests, rich upland forest slopes, and wet areas in prairies. Parasitizes a wide variety of mostly nonwoody plants.
Similar species: Several other members of the morning glory family commonly have climbing and/or twining habits, but they have green leaves and are not parasitic. Missouri has about 15 native or naturalized, climbing and/or twining species in the morning glory family, in the genera Calystegia, Convolvulus, Ipomoea, and Jacquemontia.
Habitat and Conservation
Missouri’s dodders are generally found in moist, wet, disturbed, and (frequently) open or borderline habitats, such as along streams, shores, roads, and railroads, in and near crop fields, prairies, swamps, glades, and forests. See the list of species above for each type’s particular habitats.
Dodders are found nearly worldwide and are most diverse in the tropics and subtropics. Globally, there are some 150 to 200 species. At one time, they were classified as having their own family, the Cuscutaceae, but researchers have determined they belong in the morning glory family.
Contrary to some reports, dodders do produce chlorophyll, but they do so in reduced quantities. In spring, a newly germinated dodder seed must reach a suitable host plant within about a week, or it will die. Once the young dodder comes in contact with a host plant, it twines around it and develops haustoria: suckerlike organs with modified roots that penetrate the host’s stem to draw moisture and nourishment from the host plant’s vascular system. At that point, the dodder’s root in the soil is no longer needed and withers away.
Some species of dodder are important agricultural pests and have been spread as contaminants in crop seeds. Certain dodders may parasitize crops such as soybeans, alfalfa and clover, melons, tomatoes, asparagus, and more. The parasitism may weaken or kill the host plant and may reduce yields. Also, the parasitism might open the door to other plant diseases or insect pests.
Dodder may parasitize ornamental plants, too, such as petunias, impatiens, chrysanthemums, nasturtiums, and dahlias. If dodder comes up in a place you don’t want it, remove it and the host plant before it sets seed: once in the host plant, it’s hard to kill; and the seeds, once they’re developed, can remain dormant in the soil for many years. In some species and circumstances, dodder seeds may survive in the soil for up to 20 years.
In English, the word dodder is both a noun and a verb. Although they’re spelled the same way today, apparently these began as two different words. The verb, meaning “to wobble weakly or progress feebly,” is from the Middle English dadiren. Linguists call this a frequentive verb, with its repeated “d” sounds and using the same ending as words like teeter, totter, glimmer, putter, and blabber. The noun, referring to the plant, was doder in Middle English and is related to a 13th-century Germanic word toter, which referred to egg yolk as well as the yolk-colored plant.
More word fun: dodders have several other colorful common names in English, including angel hair and witch’s hair; devil’s gut/hair/ringlet; beggarweed, fireweed, goldthread, hairweed, scaldweed, and more. It seems these plants have struck people as bizarre for a long, long time!
Why the name "love vine"? In Native American and pioneer folklore, dodders have been used as a way to determine the faithfulness of one's sweetheart. In some accounts, a piece of dodder is tossed behind one's back; it is later revisited to see if it's become attached to a plant and is still alive — if it is, then the lover is faithful. Vance Randolph reported that in the Ozarks, a young woman simply placed the piece of dodder onto a weed: "if it flourishes, her lover is faithful, and if it withers he is not to be trusted."
A very wide variety of plants may be parasitized by dodders. Some of the common nonwoody plants include members of the sunflower family (such as ragweeds, New World asters, goldenrods, thoroughworts/snakeworts, crownbeards, sneezeweeds, ironweeds, fleabane daisies, cockleburs, and sunflowers), plus smartweeds/knotweeds, spurges, milkweeds, nettles, water willow, St. John’s-worts, tick trefoils, clovers, jewelweeds, and many more. Some of our dodders may also use woody hosts, such as button bush, willows, trumpet creeper, poison ivy, hazelnut, New Jersey tea, and grapes.
Our Missouri dodders are annual plants, germinating early in the season, growing and reproducing, then dying when winter comes. In the tropics and other warm regions, where dodders are not killed by freezing weather every winter, dodders can survive for years, growing up into the tops of trees. But here in our temperate zone, dodders are generally low-growing plants, since they have to regrow from seed each year.
Apparently, mammals do not seem to feed on dodders much. Some types of bees and other insects visit the small flowers for nectar, and certain types of aphids suck the juices of dodders.