''Erigeron canadensis'' (

synonym A synonym is a word, morpheme, or phrase that means precisely or nearly the same as another word, morpheme, or phrase in a given language. For example, in the English language, the words ''begin'', ''start'', ''commence'', and ''initiate'' are a ...

''Conyza canadensis'') is an annual plant native throughout most of

North America North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...

and

Central America Central America is a subregion of North America. Its political boundaries are defined as bordering Mexico to the north, Colombia to the southeast, the Caribbean to the east, and the Pacific Ocean to the southwest. Central America is usually ...

. It is also widely naturalized in

Eurasia Eurasia ( , ) is a continental area on Earth, comprising all of Europe and Asia. According to some geographers, Physical geography, physiographically, Eurasia is a single supercontinent. The concept of Europe and Asia as distinct continents d ...

and

Australia Australia, officially the Commonwealth of Australia, is a country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...

. 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 EPSP inhibitor, inhibiting the plant enzyme 5-en ...

resistance, reported in 2001 from

Delaware Delaware ( ) is a U.S. state, state in the Mid-Atlantic (United States), Mid-Atlantic and South Atlantic states, South Atlantic regions of the United States. It borders Maryland to its south and west, Pennsylvania to its north, New Jersey ...

Description

''Erigeron canadensis'' is an

annual Annual may refer to: *Annual publication, periodical publications appearing regularly once per year **Yearbook **Literary annual *Annual plant *Annual report *Annual giving *Annual, Morocco, a settlement in northeastern Morocco *Annuals (band), a ...

herbaceous plant Herbaceous plants are vascular plants that have no persistent woody stems above ground. This broad category of plants includes many perennials, and nearly all annuals and biennials. Definitions of "herb" and "herbaceous" The fourth edition o ...

growing to tall, with sparsely hairy stems. The

leaves A leaf (: leaves) is a principal appendage of the stem of a vascular plant, usually borne laterally above ground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", while the leaves, stem, ...

are unstalked, slender, long, and up to wide, with a coarsely toothed margin. They grow in an alternate spiral up the stem, and the lower ones wither early. The

flower head A pseudanthium (; : pseudanthia) is an inflorescence that resembles a flower. The word is sometimes used for other structures that are neither a true flower nor a true inflorescence. Examples of pseudanthia include flower heads, composite flowers ...

s are produced in dense

inflorescence In botany, an inflorescence is a group or cluster of flowers arranged on a plant's Plant stem, stem that is composed of a main branch or a system of branches. An inflorescence is categorized on the basis of the arrangement of flowers on a mai ...

s and are in diameter. Each individual flower has a ring of white or pale purple

ray florets Asteraceae () is a large family of flowering plants that consists of over 32,000 known species in over 1,900 genera within the order Asterales. The number of species in Asteraceae is rivaled only by the Orchidaceae, and which is the larger fa ...

and a centre of yellow

disc floret Asteraceae () is a large family of flowering plants that consists of over 32,000 known species in over 1,900 genera within the order Asterales. The number of species in Asteraceae is rivaled only by the Orchidaceae, and which is the larger fa ...

s. The fruit is a cypsela tipped with dirty white down. ''Erigeron canadensis'' can easily be confused with ''

Erigeron sumatrensis ''Erigeron sumatrensis'' (syn. ''Conyza sumatrensis'') is an annual herb probably native to South America, but widely naturalised in tropical and subtropical regions, and regarded as an invasive weed in many places. In the British Isles it is kn ...

'', which may grow to a height of , and the more hairy ''

Erigeron bonariensis ''Erigeron bonariensis'' is a species in the family Asteraceae, found throughout the tropics and subtropics as a pioneer plant; its precise origin is unknown, but most likely it stems from Central America or South America. It has become naturaliz ...

'', which does not exceed . ''E. canadensis'' is distinguished by

bract In botany, a bract is a modified or specialized leaf, associated with a reproductive structure such as a flower, inflorescence axis or cone scale. Bracts are usually different from foliage leaves in size, color, shape or texture. They also lo ...

s that have a brownish inner surface with 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

and

and is widespread in its native range.Biota of North America Program, 2014 county distribution map, ''Erigeron canadensis''
It has spread to inhabited areas of most of the temperate zone of Asia, Europe, and

. It is found in

Britain Britain most often refers to: * Great Britain, a large island comprising the countries of England, Scotland and Wales * The United Kingdom of Great Britain and Northern Ireland, a sovereign state in Europe comprising Great Britain and the north-eas ...

from northern

Scotland Scotland is a Countries of the United Kingdom, country that is part of the United Kingdom. It contains nearly one-third of the United Kingdom's land area, consisting of the northern part of the island of Great Britain and more than 790 adjac ...

Cornwall Cornwall (; or ) is a Ceremonial counties of England, ceremonial county in South West England. It is also one of the Celtic nations and the homeland of the Cornish people. The county is bordered by the Atlantic Ocean to the north and west, ...

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

China China, officially the People's Republic of China (PRC), is a country in East Asia. With population of China, a population exceeding 1.4 billion, it is the list of countries by population (United Nations), second-most populous country after ...

Weed status

Horseweed is commonly considered a weed, and in

Ohio Ohio ( ) is a U.S. state, state in the Midwestern United States, Midwestern region of the United States. It borders Lake Erie to the north, Pennsylvania to the east, West Virginia to the southeast, Kentucky to the southwest, Indiana to the ...

Oregon Oregon ( , ) is a U.S. state, state in the Pacific Northwest region of the United States. It is a part of the Western U.S., with the Columbia River delineating much of Oregon's northern boundary with Washington (state), Washington, while t ...

, and some other locations, it has been declared a

noxious weed A noxious weed, harmful weed or injurious weed is a weed that has been designated by an agricultural or other governing authority as a plant that is harmful to agricultural or horticultural crops, natural habitats or ecosystems, or humans or lives ...

. It was the first weed to have developed

resistance, reported in 2001 from

. It can be found in fields, meadows, and gardens throughout its native range. Horseweed infestations (specifically of 105 plants per 10 ft²) 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. Soy is a staple crop, the world's most grown legume, and an important animal feed. Soy is a key source o ...

yields by as much as 83%, with one estimate claiming it can reduce yields by up to 90%. Severe infestations have reduced sugar beet yields by 64%. It is an especially problematic weed in no-till agriculture, as it is often resistant to

and other

herbicides Herbicides (, ), also commonly known as weed killers, are substances used to control undesired plants, also known as weeds.EPA. February 201Pesticides Industry. Sales and Usage 2006 and 2007: Market Estimates. Summary in press releasMain page f ...

. Farmers are advised to include

2,4-D 2,4-Dichlorophenoxyacetic acid is an organic compound with the chemical formula . It is usually referred to by its ISO common name 2,4-D. It is a systemic herbicide that kills most broadleaf weeds by causing uncontrolled growth, but most gra ...

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

in a burndown application prior to planting to control horseweed.

Uses

The

Zuni people The Zuni (; formerly spelled ''Zuñi'') are Native American Pueblo peoples native to the Zuni River valley. The Zuni people today are federally recognized as the Zuni Tribe of the Zuni Reservation, New Mexico, and most live in the Pueblo o ...

insert the crushed flowers of ''E. canadensis'' var. ''canadensis'' into the

nostrils A nostril (or naris , : 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 turbinates, ...

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 a ...

, 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, irritant ...

. Other Native Americans have 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.

Gallery

Standard form

Erigeron canadensis from Antalya by D Merrick 08.jpg, General form, may be light green, inflorescence fairly tight Erigeron canadensis from Britain by D Merrick 15.jpg, Stemmy form Erigeron canadensis from Antalya by D Merrick 05.jpg, Flower head, hairless or mostly so, ray petals small but conspicuous, base of head not widely bulging Erigeron canadensis from Antalya by D Merrick 06.jpg, Flower head, angled Erigeron canadensis from Antalya by D Merrick 02.jpg, Flower head face on Erigeron canadensis from Antalya by D Merrick 07.jpg, Individual flowers in the head Erigeron canadensis from Britain by D Merrick 13.jpg, Hair profile of leaf, projecting at base usually, directed forward at tip Erigeron canadensis from Antalya by D Merrick 03.jpg, Leaf tip with forward hairs not curving inward Erigeron canadensis from Antalya by D Merrick 04.jpg, Leaf surfaces not hairy Erigeron canadensis from Antalya by D Merrick 01.jpg, Leaf bases near stem showing projecting hairs Erigeron canadensis from Antalya by D Merrick 09.jpg, May become large

Other forms

Erigeron canadensis from Antalya by D Merrick 107.jpg, Biennial growing in sand by a river from a surviving stem Erigeron canadensis Kurşunlu in Antalya by D Merrick 02.jpg, Biennial with ad-hoc branching Erigeron canadensis Kurşunlu in Antalya by D Merrick 01.jpg, Form with broken biennial stem top Erigeron canadensis from Antalya by D Merrick 105.jpg, Unusual spike-like form growing in winter Conyza-canadensis-seeds.jpg, seeds Canadese fijnstraal plant Conyza canadensis.jpg,

References

External links

{{Authority control canadensis Flora of Northern America Plants used in traditional Native American medicine Plants described in 1753 Ruderal species Taxa named by Carl Linnaeus