Ambrosia trifida, the giant ragweed, is a species of flowering plant in the sunflower family. It is native to North America, where it is widespread in Canada, the United States, and northern Mexico.[1] It is present in Europe and Asia as an introduced species, and it is known as a common weed in many regions.[3] Its common names include great ragweed, Texan great ragweed, giant ragweed, tall ragweed, blood ragweed, perennial ragweed, horseweed,[4] buffaloweed, and kinghead.[5]

Ambrosia trifida
Ambrosia trifida (inflorescences).jpg

Secure (NatureServe)
Scientific classification edit
Kingdom: Plantae
Clade: Tracheophytes
Clade: Angiosperms
Clade: Eudicots
Clade: Asterids
Order: Asterales
Family: Asteraceae
Genus: Ambrosia
A. trifida
Binomial name
Ambrosia trifida
  • Ambrosia aptera DC.
  • Ambrosia integrifolia Muhl. ex Willd.


This is an annual herb usually growing up to 2 m (6 ft 7 in) tall, but known to reach over 6 m (20 ft) in rich, moist soils. The tough stems have woody bases and are branching or unbranched.[5] Most leaves are oppositely arranged. The blades are variable in shape, sometimes palmate with five lobes, and often with toothed edges. The largest can be over 25 cm (9.8 in) long by 20 cm (7.9 in) wide. They are borne on petioles several centimeters long. They are glandular and rough in texture. The species is monoecious, with plants bearing inflorescences containing both pistillate and staminate flowers. The former are clustered at the base of the spike and the latter grow at the end. The fruit is a bur a few millimeters long tipped with several tiny spines.[1][6]

As a weedEdit

This species is well known as a noxious weed, both in its native range and in areas where it is an introduced and often invasive species.[7][8] It is naturalized in some areas, and it is recorded as an adventive species in others.[3] It grows in many types of disturbed habitat, such as roadsides, and in cultivated fields. Widespread seed dispersal occurs when its spiny burs fall off the plant and are carried to new habitat by people, animals, machinery, or flowing water. The plant is destructive to native and crop plants because it easily outcompetes them for light.[5]

As an allergenEdit

Also, interest is great in preventing the spread of this plant because its pollen is a significant human allergen.[9] It is one of the most familiar allergenic ragweeds, and residents of different regions begin to experience allergic symptoms as the plant spreads into the area.[10]


Native Americans had a number of uses for the plant as traditional medicine. The Cherokee used it as a remedy for insect stings, hives, fever, and pneumonia, and the Iroquois used it to treat diarrhea.[11]

Giant ragweed has been used successfully as a compost activator and an ingredient in sheet mulch gardens.[12]



  1. ^ a b c Ambrosia trifida. Flora of North America.
  2. ^ The Plant List Ambrosia trifida L.
  3. ^ a b "Ambrosia trifida". Germplasm Resources Information Network (GRIN). Agricultural Research Service (ARS), United States Department of Agriculture (USDA). Retrieved 22 December 2017.
  4. ^ Ambrosia trifida. Integrated Taxonomic Information System (ITIS).
  5. ^ a b c Ambrosia spp. Encycloweedia. California Department of Food and Agriculture.
  6. ^ Ambrosia trifida. The Jepson eFlora 2013.
  7. ^ Flora of China Vol. 20-21 Page 877 三裂叶豚草 san lie ye tun cao Ambrosia trifida Linnaeus, Sp. Pl. 2: 987. 1753.
  8. ^ Altervista Flora Italiana, Ambrosia trifida L. includes photos and European distribution map
  9. ^ Ghosh, B., et al. (1991). Cloning the cDNA encoding the AmbtV allergen from giant ragweed (Ambrosia trifida) pollen. Gene 101(2), 231-38.
  10. ^ Makra, L., et al. (2005). The history and impacts of airborne Ambrosia (Asteraceae) pollen in Hungary. Grana 44(1), 57-64.
  11. ^ Ambrosia trifida. Native American Ethnobotany. University of Michigan, Dearborn.
  12. ^ Stallings, Ben (2014-06-20). "Ragweed: Curse or Blessing, the Choice is Yours". Permaculture News. Permaculture Research Institute. Retrieved 27 June 2014.

External linksEdit