Name: Cuscuta epithymum Murray
Family: Convolvulaceae, the morning glory family. Some consider members of the genus Cuscuta to form a separate family, the Cuscutaceae.
Common Names: Clover Dodder, Lesser Clover Dodder, Lesser Dodder, Thyme Dodder (4,10). Common names for the genus Cuscuta: are Dodder, Love Vine, Angel’s Hair, Tangle Gut, Strangle Vine, Devil’s Gut, Witches’ Shoelaces (8).
Etymology: In Latin, Cuscuta means Dodder. However, Cuscuta is thought by some to have Arabic origins in the word “Kushkut.” The specific epithet suggests the plant that this dodder was found growing on: Thyme. The Greek prefix “epi“ means upon or over, and “thymum” is Latin for thyme (2,10,11,12).
Botanical synonyms (14): Cuscuta epithymum Sievers ex Ledeb., Cuscuta epithymum Webb & Berthel., Cuscuta epithymum Thuill., Cuscuta epithymum Bové ex Choisy
Quick Notable Features:
¬ Leafless, reddish-purple parasitic vine, usually found in a stringy mass over its host (8,10,18).
¬ Small white to pink flowers, even reddish (2,5,18).
¬ Herbaceous, usually an annual (5,8).
¬ Very small, rough seeds that are dull gray or light brown in color (3,4,5,8,18).
Plant Height: It has been reported that stems from a single dodder plant can reach a 0.5mile in length, if the host is large enough (9,18).
Subspecies/varieties recognized (13):
C. epithymum var. alba (J. Presl & C. Presl) Trab.
C. epithymum var. angustissima (Engelm.) Yunck.
C. epithymum var. kotschyi (Des Moul.) Engelm.
C. epithymum var. macranthera (Held. & Sartoni) Engelm.
C. epithymum var. obtusata Engelm.
C. epithymum var. rubella (Engelm.) Trab.
C. epithymum var. sagittanthera Engelm.
C. epithymum var. scabrella Engelm.
C. epithymum var. vulgaris Engelm
Most Likely Confused with: C. epithymum can be confused with other species in the genus Cuscuta. Nine other species of Cuscuta occur in Michigan. Worldwide, C. epithymum is often confused with Cuscuta europea and Cuscuta epilinum, its closest relatives (2,4,7). It might also be confused with morning glories (Ipomoea), especially the thinner-stemmed species.
Habitat Preference: C. epithymum is most commonly found growing on Red Clover or Thyme, but it may also parasitize other plants, including alfalfa. C. epithymum is most often found in agricultural areas throughout the warm and temperate regions of the world. However, it has also been reported in tropical areas such as Fiji and Tahiti, among others. C. epithymum occurs not only worldwide, but also in many habitats. Its optimal germination temperature in a greenhouse is 15º C. Under favorable conditions, this species is cabable of living through winter (1,3,5,10).
Geographic Distribution in Michigan: C. epithymum is documented from Oceana, Calhoun, Hillsdale, Washtenaw, Macomb, and St. Clair counties (1).
Complete Geographic Distribution: Native to Europe, Cuscuta epithymum can now be found throughout the world. In North America, it is found in the United States (CA, CT, IA, KY, MA, MD, ME, MI, MO, MT, ND, NE, NJ, NM, NV, NY, OH, OR, PA, RI, SD, VA,VT,WA,WV,WY) and Canada (BC, NB, ON) Cuscuta epithymum is known for infesting crops – particularly legumes, in Europe and around the world. It was spread globally, introduced by the seed trade (3,5,8,10).
Parasitism: Plant parasitism is a type of symbiotic relationship in which plants obtain nutrients directly from another plant. Although parasitic plants are commonly known to lack chlorophyll, some species have green organs, making them partially autotrophic. The physical link between the parasite and the host is called a “haustorium”, and often creates a xylem-to-xylem attachment. The parasite host can vary, ranging from the mycorrhizae of trees, to grasses and hardwood trees. The parasite often maintains open or partially open stomata, allowing transpiration to aid in extracting nutrients from the host. A parasitic plant may either be hemiparasitic, meaning it performs some photosynthesis and can survive on its own, or holoparasitic, meaning it performs no photosynthesis and depends entirely on the host for nutrients. Typically, holoparasitic plants do not contain chloroplasts (6,21,22).
Vegetative Plant Description: Upon germination, the seedlings, each with small anchorage roots, begin to actively bend around in a circle, in search of a host. Once a seedling finds a host, it attaches and begins to form haustoria. After locating a host, the anchorage roots die. The stems of Cuscuta epithymum are less than 0.4mm in diameter and vary from light red to dark purple. Very small alternate leaves may be present, but these do not serve a function. Cuscuta epithymum is holoparasitic and does not perform photosynthesis (3,5,8,21,22).
Climbing Mechanism: Stems of Cuscuta epithymum twine using their stems in a dextral orientation (3, KW pers. obs.). Although specific information for the climbing mechanism of Cuscuta epithymum was not found, the following information pertains to the genus of Cuscuta in general. Species of Cuscuta utilize two types of coiling: one in which the coils are tight with numerous haustoria, and the other in which coils are loose with few haustoria. Both types of coiling may be present in one individual plant (9). It has been observed that stems of Cuscuta species rarely twine more than three times around a single host branch (15).
Flower Description: The small flowers are sessile, 2-3mm long from base to corolla sinuses, white-pink to purplish, and borne in compact clusters. The calyx is shorter than or equal in length to the corolla tube, the corolla lobes are triangular and acute. The 5 stamens are shorter than the corolla lobes, with filaments longer than anthers. The ovary is globose, stigmas oblong, style and stigma are twice as long as the ovary (3,5,8,10,17).
Flowering Time: Mid-July to late September (21).
Pollinator: Cuscuta epithymum is capable of both cross-pollination and self- pollination. Many different species of insects may contribute to pollination. One study indicated that ants were some of the main pollinators, while another observed visits to the flowers by species of bees, wasps, flies and other insects, collectively from 8 families of insects (20, 21).
Fruit Type and Description: The fruit is a globose, circumscissile capsule, topped by the withered corolla. Fruits usually contain 4 seeds (3, 5, 8).
Seed Description: Seeds are very small, about 1mm in length. Rough, angled, and compressed-ovoid. The hilum is short, oblong, and transverse. The shape of a seed depends on how many seeds it developed with, because they develop alongside each other in the ovary. One Cuscuta epithymum plant was reported to produce 16,000 seeds (3,5,8,9).
Dispersal Syndrome: The genus Cuscuta is generally described as unspecialized or haphazard in dispersal. However, germination of the seeds of most parasitic plants require a signal from a suitable host; therefore, the dispersal syndromes of successful species of Cuscuta should ensure close proximity to the desired host (6, 9).
Distinguished by: Cuscuta epithymum can be distinguished from Cuscuta europea by its purplish stems and sessile stamens and the fact that C. europea does not occur in Michigan. Cuscuta epithymum can be distinguished from Cuscuta epilinum by its pink to red flowers, triangular calyx-lobes, spreading corolla lobes and included stamens. Although Cuscuta epithymum may be confused with some thin-stemmed species of Ipomoea and Fallopia, it is important to note that the flowers of C. epithymum are very small, where flowers of Ipomoea species are large and bell shaped. Also, one of the most important traits of C. epithymum is that it has only very small, scale-like, non-functioning leaves. Species of both Ipomoea and Fallopia have functional leaves that are much larger in size (2,5,7,9,10).
Other members of the family in Michigan: Calystegia (10), Convolvulus (2), Cuscuta (10) and Ipomoea (4) (source: 1).
Ethnobotanical Uses: In medieval times, the health benefits of dodders were believed to be determined by their respective hosts. C. epithymum occurred frequently on thyme. Thus, because thyme was considered – figuratively, not literally – a hot, dry plant, it was believed that C. epithymum was therapeutic because of its warm characteristics. It was also believed that when ground up and mixed with dog blood or other plants, C. epithymum would help keep an individual safe from evil spirits (12).
Phylogenetic Information: The Convolvulaceae are placed in the order Solanales. Solanales and Lamiales are a monophyletic group in the Asterid 1 clade. Within Convolvulaceae there are 3 – 4 distinct subfamilies. Cuscuta belongs to Convolvuloideae (16, 17).
Interesting Quotation or Other Interesting Factoid not inserted above: Cuscuta earned the common name “love vine” because of a Native American Pawnee belief. A girl would pluck part of a vine and throw it behind her while thinking of a certain someone. If, on the next day, the parasitic vine had reattached itself, it was a sign that the certain someone would be a good suitor. Perhaps similar to the “He loves me, he loves me not” idea in Western culture (21, 23).
Literature and websites used:
- Voss, E.G. 2004. Michigan Flora Part III: Dicots Concluded. Ann Arbor, Michigan: Cranbrook Institute of Science.
- Fernald, M. L. 1950. Gray’s Manual of Botany, 8th ed. New York: American Book Company.
- McGregor, R.L. 1986. Flora of the Great Plains. Lawrence, Kansas: The University Press of Kansas.
- USDA, NRCS. 2008. The PLANTS Database, Version 3.1, National Plant Data Center, Baton Rouge, LA 70874-4490. http://plants.usda.gov/ (February 25, 2011)
- Holm, L., J. Doll, E. Holm, J. Pancho, and J. Herberger 1997. World Weeds: Natural Histories and Distribution. New York, NY: John Wiley & Sons, Inc.
- Clark, W.D., R. Moore, and K.R. Stern 1995. Botany. Dubuque, Iowa: Wm. C. Brown Publ.
- Song, H. 2006. Flora of Pakistan. http://www.efloras.org/florataxon.aspx?flora_id=5&taxon_id=250013550
- Yuncker, T.G. 1965. Cuscuta. North American Flora II(4): 1-51.
- Kuijt, J. 1969. The Biology of Parasitic Flowering Plants. Los Angeles, CA: University of California Press.
- Beal, W.J. 1915. Michigan Weeds. Michigan Agricultural College, Experiment Station: University of Michigan. Bulletin 267 (2nd edition), 181p.
- Brown, R.W. 1956. Composition of Scientific Words. Washington, D.C: Smithsonian Institution Press.
- Costea, M. and F.J. Tardif 2004. Cuscuta (Convolvulaceae) – The strength of weakness: A history of its name, uses, and parasitism concept during ancient and medieval times. Sida 21: 369-378.
- Tropicos.org. Missouri Botanical Garden. 26 Apr 2011 http://www.tropicos.org
- The International Plant Names Index 2008. Published on the Internet http://www.ipni.org [accessed: March 2nd, 2011].
- Willis, J.C. revised 1966. Dictionary of the Flowering Plants and Ferns. Cambridge University Press.
- Stevens, P.F. Angiosperm Phylogeny Website. Version 7, May 2006. http://www.mobot.org/MOBOT/research/APweb
- Zomlefer, W.B. 1994. Guide to Flowering Plant Families. Chapel Hill, North Carolina: The University of North Carolina.
- Kruckeberg, A.R. 1991. The Natural History of Puget Sound Country. Seattle, Washington: University of Washington Press.
- Menninger, E.A. 1970. Flowering Vines of the World. New York, New York: Hearthside Press Incorporated.
- Gómez M. J. 1994. Importance of direct and indirect effects of the interaction between a parasitic Angiosperm (Cuscuta epithymum) and its host plant (Hormathophylla spinosa). Oikos 71(1): 97-106.
- Meulebrouk, K. 2009. Distribution, demography and metapopulation dynamics of C. epithymum in managed heathlands. Dissertationes de Agricultura. 50-53.
- UCLA Botanical Gardens, Textbook Section on Life Forms http://www.botgard.ucla.edu/
- Costea, M. 2007-onwards. Digital Atlas of Cuscuta (Convolvulaceae). Wilfrid Laurier University Herbarium, Ontario, Canada. http://www.wlu.ca/page.php?grp_id=2147&p=9047
Image Credits (all used with permission):
1) Image of stringy leafless stems courtesy of Gill Smith and Jane Smyth of the Ryedale Natural History Society taken at Gundale (http://www.ryenats.org.uk/gundale/gundaleindex.htm)
2) Image of twining courtesy of Gill Smith and Jane Smyth of the Ryedale Natural History Society taken at Gundale (http://www.ryenats.org.uk/gundale/gundaleindex.htm)
3) Image of flower cluster courtesy of D. L. Nickrent (Southern Illinois University) through the PhytoImages Website (http://126.96.36.199/index.html)
4) Image of seeds courtesy of Steve Hurst from USDA-NRCS PLANTS Database, plants.usda.gov.
5) Species distribution map, derived from the Michigan Flora Online.
Primary Author: Karie Whitman; Parasitism section by Lauren S. Sopher and Karie Whitman; additions by John Bradtke; editing by Robyn J. Burnham.
© Robyn J. Burnham, University of Michigan
For additional information on Michigan Plant Diversity species accounts, please contact Robyn J. Burnham via email: rburnham“at”umich.edu