''Erigeron canadensis'' ( synonym ''Conyza canadensis'') is an annual plant native throughout most of North America and

Central America Central America ( es, América Central or ) is a subregion of the Americas. Its boundaries are defined as bordering the United States to the north, Colombia to the south, the Caribbean Sea to the east, and the Pacific Ocean to the west. ...

. It is also widely naturalized in

Eurasia Eurasia (, ) is the largest continental area on Earth, comprising all of Europe and Asia. Primarily in the Northern and Eastern Hemispheres, it spans from the British Isles and the Iberian Peninsula in the west to the Japanese archipelago ...

and Australia. Common names include horseweed, Canadian horseweed, Canadian fleabane, coltstail, marestail, and butterweed. It was the first weed to have developed

glyphosate Glyphosate (IUPAC name: ''N''-(phosphonomethyl)glycine) is a broad-spectrum systemic herbicide and crop desiccant. It is an organophosphorus compound, specifically a phosphonate, which acts by inhibiting the plant enzyme 5-enolpyruvylshik ...

resistance, reported in 2001 from

Delaware Delaware ( ) is a state in the Mid-Atlantic region of the United States, bordering Maryland to its south and west; Pennsylvania to its north; and New Jersey and the Atlantic Ocean to its east. The state takes its name from the adjacent Del ...

Description

''Erigeron canadensis'' is an annual plant growing to 1.5 m (60 in) tall, with sparsely hairy stems. The leaves are unstalked, slender, 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

flower A flower, sometimes known as a bloom or blossom, is the reproductive structure found in flowering plants (plants of the division Angiospermae). The biological function of a flower is to facilitate reproduction, usually by providing a mechani ...

s are produced in dense

inflorescence An inflorescence is a group or cluster of flowers arranged on a Plant stem, stem that is composed of a main branch or a complicated arrangement of branches. Morphology (biology), Morphologically, it is the modified part of the shoot of sperma ...

s 1 cm in diameter. Each individual flower has a ring of white or pale purple

ray florets The family Asteraceae, alternatively Compositae, consists of over 32,000 known species of flowering plants in over 1,900 genera within the order Asterales. Commonly referred to as the aster, daisy, composite, or sunflower family, Compositae w ...

and a centre of yellow disc florets. The fruit is a cypsela tipped with dirty white down. ''Erigeron canadensis'' can easily be confused with '' Erigeron sumatrensis'', which may grow to a height of , 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.

Distribution and habitat

Horseweed originated in North America and is very widespread there,Biota of North America Program, 2014 county distribution map, ''Erigeron canadensis''
/ref> but has spread to inhabited areas of most of the temperate zone of Asia, Europe, and Australia. It is found in

Britain Britain most often refers to: * The United Kingdom, a sovereign state in Europe comprising the island of Great Britain, the north-eastern part of the island of Ireland and many smaller islands * Great Britain, the largest island in the United King ...

from northern

Scotland Scotland (, ) is a Countries of the United Kingdom, country that is part of the United Kingdom. Covering the northern third of the island of Great Britain, mainland Scotland has a Anglo-Scottish border, border with England to the southeast ...

Cornwall Cornwall (; kw, Kernow ) is a historic county and ceremonial county in South West England. It is recognised as one of the Celtic nations, and is the homeland of the Cornish people. Cornwall is bordered to the north and west by the Atlantic ...

, growing as a weed of arable land and man-made environments. It is considered invasive in China.

Weed status

Horseweed is commonly considered a weed, and in

Ohio Ohio () is a state in the Midwestern region of the United States. Of the fifty U.S. states, it is the 34th-largest by area, and with a population of nearly 11.8 million, is the seventh-most populous and tenth-most densely populated. The sta ...

, 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 The soybean, soy bean, or soya bean (''Glycine max'') is a species of legume native to East Asia, widely grown for its edible bean, which has numerous uses. Traditional unfermented food uses of soybeans include soy milk, from which tofu a ...

yields by as much as 83%. It is an especially problematic weed in no-till agriculture, as it is often resistant to

and other herbicides. Farmers are advised to include 2,4-D or

dicamba Dicamba (3,6-dichloro-2-methoxybenzoic acid) is a broad-spectrum herbicide first registered in 1967. Brand names for formulations of this herbicide include Dianat, Banvel, Diablo, Oracle and Vanquish. This chemical compound is a chlorinated de ...

in a burndown application prior to planting to control horseweed.

Uses

The Zuni people insert the crushed flowers of ''E. canadensis'' var. ''canadensis'' into the

nostrils A nostril (or naris , plural ''nares'' ) is either of the two orifices of the nose. They enable the entry and exit of air and other gasses through the nasal cavities. In birds and mammals, they contain branched bones or cartilages called turbi ...

to cause

sneezing A sneeze (also known as sternutation) is a semi-autonomous, convulsive expulsion of air from the lungs through the nose and mouth, usually caused by foreign particles irritating the nasal mucosa. A sneeze expels air forcibly from the mouth and ...

, relieving

rhinitis Rhinitis, also known as coryza, is irritation and inflammation of the mucous membrane inside the nose. Common symptoms are a stuffy nose, runny nose, sneezing, and post-nasal drip. The inflammation is caused by viruses, bacteria, irrita ...

. Other Native Americans used a preparation of the plant's leaves to treat sore throat and dysentery. 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 Fire making, fire lighting or fire craft is the process of artificially starting a fire. It requires completing the fire triangle, usually by heating tinder above its autoignition temperature. Fire is an essential tool for human survival and ...

. Image:Conyza-canadensis-seeds.jpg Image:Canadese fijnstraal plant Conyza canadensis.jpg

References

External links

{{Taxonbar, from1=Q21874197, from2=Q794305 canadensis Flora of North America Plants used in traditional Native American medicine Plants described in 1753 Ruderal species Taxa named by Carl Linnaeus