Erigeron canadensis

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Erigeron canadensis
In the Netherlands in 2004
Scientific classification edit
Kingdom: Plantae
Clade: Tracheophytes
Clade: Angiosperms
Clade: Eudicots
Clade: Asterids
Order: Asterales
Family: Asteraceae
Genus: Erigeron
E. canadensis
Binomial name
Erigeron canadensis
  • Aster canadensis (L.) E.H.L.Krause
  • Caenotus canadensis (L.) Raf.
  • Caenotus pusillus Raf.
  • Conyza canadensis (L.) Cronquist
  • Conyza parva Cronquist
  • Conyzella canadensis (L.) Rupr.
  • Erigeron myriocephalus Rech.f. & Edelb.
  • Erigeron paniculatus Lam.
  • Erigeron pusillus Nutt.
  • Erigeron ruderalis Salisb.
  • Erigeron strictus DC.
  • Inula canadensis Bernh.
  • Leptilon canadense (L.) Britton
  • Leptilon pusillum (Nutt.) Britton
  • Marsea canadensis (L.) V.M.Badillo
  • Senecio ciliatus Walter
  • Tessenia canadensis (L.) Bubani
  • Trimorpha canadensis (L.) Lindm.
Canadian fleabane (Erigeron canadensis) essential oil in a clear glass vial

Erigeron canadensis (synonym Conyza canadensis) is an annual plant native throughout most of North America and Central America. It is also widely naturalized in Eurasia and Australia.[2] Common names include horseweed, Canadian horseweed, Canadian fleabane, coltstail, marestail, and butterweed. It was the first weed to have developed glyphosate resistance, reported in 2001 from Delaware.[3]


Erigeron canadensis is an annual plant growing to 1.5 m (60 in) tall, with sparsely hairy stems. The leaves are unstalked, slender, 2–10 centimetres (0.79–3.94 in) long, and up to 1 cm (0.4 inches) across, with a coarsely toothed margin. They grow in an alternate spiral up the stem and the lower ones wither early. The flowers are produced in dense inflorescences 1 cm in diameter. Each individual flower has a ring of white or pale purple ray florets and a centre of yellow disc florets. The fruit is a cypsela tipped with dirty white down.[4]

Erigeron canadensis can easily be confused with Erigeron sumatrensis, which may grow to a height of 2 m, and the more hairy Erigeron bonariensis, which does not exceed 1 m (40 in). E. canadensis is distinguished by bracts that have a brownish inner surface and no red dot at the tip, and are free (or nearly free) of the hairs found on the bracts of the other species.[5][6][7]

Distribution and habitat[edit]

Horseweed originated in North America and is very widespread there,[2] but has spread to inhabited areas of most of the temperate zone of Asia,[8] Europe,[4][9] and Australia.[10] It is found in Britain from northern Scotland to Cornwall, growing as a weed of arable land and man-made environments. It considered invasive in China.[11]

Weed status[edit]

Horseweed is commonly considered a weed, and in Ohio, it has been declared a noxious weed.[12] It can be found in fields, meadows, and gardens throughout its native range. Horseweed infestations have reduced soybean yields by as much as 83%.[citation needed] It is an especially problematic weed in no-till agriculture, as it is often resistant to glyphosate[3] and other herbicides.[13] Farmers are advised to include 2,4-D or dicamba in a burndown application prior to planting to control horseweed.[citation needed]


The Zuni people insert the crushed flowers of E. canadensis var. canadensis into the nostrils to cause sneezing, relieving rhinitis.[14] Other Native Americans used a preparation of the plant's leaves to treat sore throat and dysentery.[15] A tincture can be made from the dried flowering tops of the plants.

Horseweed is a preferable material for use in the hand drill-method of making friction fire.[4]


  1. ^ a b "Erigeron canadensis L." Plants of the World Online. Royal Botanic Gardens, Kew. Retrieved 2020-08-16.
  2. ^ a b Biota of North America Program, 2014 county distribution map, Erigeron canadensis
  3. ^ a b VanGessel, Mark J. (2001). "Glyphosate-resistant horseweed from Delaware". Weed Science. 49 (6): 703–705. doi:10.1614/0043-1745(2001)049[0703:RPRHFD]2.0.CO;2. JSTOR 4046416.
  4. ^ a b c "Canadian Fleabane: Conyza canadensis". NatureGate. Retrieved 2013-12-31.
  5. ^ Conyza sumatrensis, International Environmental Weed Foundation
  6. ^ Green, Deane (31 August 2011). "Horseweed, Marestail". Retrieved 2014-08-09.
  7. ^ Flora of North America, Conyza canadensis (Linnaeus) Cronquist, Bull. Torrey Bot. Club. 70: 632. 1943. Vergerette du Canada
  8. ^ Flora of China, Erigeron canadensis Linnaeus, Sp. Pl. 2: 863. 1753. 小蓬草 xiao peng cao
  9. ^ Altervista Flora Italiana, Cespica canadese, avoadinha, Berufkraut, Erigeron canadensis L. includes photos and European distribution map
  10. ^ Atlas of Living Australia, Conyza canadensis (L.) Cronquist Canadian Fleabane
  11. ^ Wu, Bingde; Zhang, Huanshi; Jiang, Kun; Zhou, Jiawei; Wang, Congyan (2019). "Erigeron canadensis affects the taxonomic and functional diversity of plant communities in two climate zones in the North of China". Ecological Research. 34 (4): 535–547. doi:10.1111/1440-1703.12024.
  12. ^ "Erigeron canadensis, Conyza canadensis". Germplasm Resources Information Network (GRIN). Agricultural Research Service (ARS), United States Department of Agriculture (USDA). Retrieved 2017-12-18. {{citation}}: Check |url= value (help)
  13. ^ Kruger, Greg R.; Davis, Vince M.; Weller, Stephen C.; Johnson, William G. (2010). "Growth and Seed Production of Horseweed (Conyza canadensis) Populations after Exposure to Postemergence 2,4-D". Weed Science. 58 (4): 413–419. doi:10.1614/WS-D-10-00022.1. S2CID 55366555.
  14. ^ Stevenson, Matilda Coxe 1915 Ethnobotany of the Zuni Indians. SI-BAE Annual Report #30 (p.55).
  15. ^ Niering, William A.; Olmstead, Nancy C. (1985) [1979]. The Audubon Society Field Guide to North American Wildflowers, Eastern Region. Knopf. p. 377. ISBN 0-394-50432-1.

External links[edit]

Media related to Erigeron canadensis at Wikimedia Commons