Conyza canadensis

Conyza canadensis
File:Conyza-canadensis-plant.jpg
photo taken in Netherlands in 1984
Scientific classification
Kingdom:	Plantae
(unranked):	Angiosperms
(unranked):	Eudicots
(unranked):	Asterids
Order:	Asterales
Family:	Asteraceae
Tribe:	Astereae
Genus:	Conyza
Species:	C. canadensis
Binomial name
Conyza canadensis (L.) Cronquist
Synonyms
Synonymy Erigeron canadensis L. Aster canadensis (L.) E.H.L.Krause 1905 not (L.) Kuntze 1891 Caenotus canadensis (L.) Raf. Caenotus pusillus (Nutt.) Raf. Conyzella canadensis (L.) Rupr. Erigeron myriocephalus Rech.f. & Edelb. Erigeron pusillus Nutt. Erigeron setiferus Post ex Boiss. Leptilon canadense (L.) Britton & Brown Leptilon canadense (L.) Britton & A.Br. Leptilon pusillum (Nutt.) Britton Marsea canadensis (L.) V.M.Badillo Senecio ciliatus Walter Trimorpha canadensis (L.) Lindm.

File:CanadianFleabaneEssentialOil.png

Canadian fleabane (Conyza canadensis) essential oil in a clear glass vial

Conyza canadensis (sometimes called Erigeron canadensis L.) is an annual plant native throughout most of North America and Central America. It is also widely naturalized in Eurasia and Australia. 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.

Description

Conyza canadensis is an annual plant growing to 1.5 m (60 inches) tall, with sparsely hairy stems. The leaves are unstalked, slender, 2–10 cm 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.

Conyza canadensis can easily be confused with C. sumatrensis, which may grow to a height of 2 m, and the more hairy C. bonariensis which does not exceed 1 m (40 inches). Conyza 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.

Distribution and habitat

Horseweed originated in North America and is very widespread there, but has spread to inhabited areas of most of the temperate zone of Asia, Europe, and Australia. It is much the most common of the alien Conyza species in Britain, and is found from northern Scotland to Cornwall. It is the only one of the British Conyza species that grows as a weed of arable land: the others are casuals of waste and disturbed ground in towns and by roads and railways. It is not invasive of any natural or semi-natural habitats.

Weed status

Horseweed is commonly considered a weed, and in Ohio it has been declared a noxious weed. It can be found in fields, meadows, and gardens throughout its native range. Horseweed infestations have reduced soybean yields by as much as 83%. It is an especially problematic weed in no-till agriculture, as it is often resistant to glyphosate and other herbicides. Farmers are advised to include 2,4-D or dicamba in a burndown application prior to planting to control horseweed. Horseweed was the first weed shown to be glyphosate resistant in 2001. Experiments show that horseweed can develop resistance to 2,4-D.

Uses

The Zuni people insert the crushed flowers of C. canadensis var. canadensis into the nostrils to cause sneezing, relieving rhinitis. 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.

References

• A. Davis, K. Renner, C. Sprague, L. Dyer, D. Mutch (2005). Integrated Weed Management. MSU.
• ISBN 0-89672-614-2

External links

• Conyza canadensis, ITIS Report

• Conyza-canadensis-seeds.jpg
• Canadese fijnstraal plant Conyza canadensis.jpg