Cuscuta spp., Dodder

Family

Convolvulaceae, the Morning-glory Family

Distinguishing Characteristics

All dodders are rapidly growing, twining, parasitic vines, without chlorophyll. These parasitic species have minimal plant structures, with roots present only on young plants and leaves inconspicuous or absent. The stems are yellowish or orange, threadlike, and fleshy, with tooth-like projections called “haustoria” that penetrate the phloem (sugar-transporting tissue) of the host plant. The flowers are tiny, about 1/8 inch in diameter, often borne in dense clusters, with white, somewhat bell-shaped, corollas that have five slightly reflexed lobes (as seen with magnification). The pistil has either two separate or united styles. The fruit is a whitish berry, opening by a cap-like lid in some species, or more commonly, disintegrating on the vine or on the soil and releasing the seeds gradually.

Distribution

The genus contains about 150 species with a worldwide distribution. In this country, one or more species is found in every state, except Alaska. Many species are restricted to a single host, but others have a wide host range. All species native to Florida belong in the latter category.

Occurrence in Florida

Eight species are native in Florida, and of these, Cuscuta pentagona is the most widely distributed, but at least one of these species is found in almost every county. Of the exotic species, only C. japonica has been collected in Florida and that only in Gadsden County. The native species include C.  americana, C. compacta, C. exaltata, C. gronovii, C. indecora, C. obtusiflora, C. pentagona, and C. umbellata.

Similar Species in Florida

When it is not flowering or fruiting, the love vine or woe vine, Cassytha filiformis in the Laurel family (Lauraceae), is virtually indistinguishable from dodders, but it is more tropical or subtropical in its distribution. The love vine contains some chlorophyll, and the stems are green when young, but quickly become orange. Stems emit a pungent odor when crushed. In contrast, the stems of dodders are orange from the beginning and are not aromatic when crushed. The fruits of the love vine are about 1/4 inch in diameter, green with black seeds, and are borne singly along the stem. Those of dodders are about 1/8 inch in diameter, whitish, and appear in dense clusters. In general, the love vine attacks woody plants while dodders infest herbaceous plants, but there are many exceptions.

Means of Dispersal

Dodders produce abundant seeds that must be scarified, by natural weathering or fungal attacks, before they will germinate. The seeds can remain viable in the soil for a period of 20 years or more.

Comments

Dodders are obligate parasites, completely dependent on their host plant for nutrition. They generally do not kill their host, but can substantially weaken it. A few plants, such as grasses and other monocots, appear to be immune from infestation. Dodders are difficult to control once established and move rapidly from plant to plant, especially in a nursery situation. Herbicides generally kill the host as well as the parasite. Manual removal can also be successful on a small scale, but vigilance is required, since overlooked pieces can regenerate the parasite. Plants of all species are frost-susceptible and perish during the winter, at least in northern Florida.

Florida’s noxious weed list excludes native species of Cuscuta, but all dodder species are considered plant pests that reduce the viability of nursery stock. Plant pests include any living stage (as well as reproductive parts) of parasitic plants that can injure or damage any plant. Parasitic plants in nursery stock are subject to quarantine to prevent the spread of the pest (F.S. 581.011).

Further Information

• Haynes, A.R., N.C. Coile, and T.S. Schubert. 1996. Comparison of Two Parasitic Vines: Dodder (Cuscuta) and Woe Vine (Cassytha). Botany Circular # 30. Division of Plant Industry, Gainesville, Florida.  https://www.fdacs.gov/content/download/12624/file/boteirc30 [ 913 kB ] [accessed September 22, 2015].