Conyza canadensis
Encyclopedia
Conyza canadensis is an annual plant native throughout most of North America
and Central America
. Common names include Horseweed, Canadian Horseweed, Canadian Fleabane, Coltstail, Marestail and Butterweed.
It is an annual plant
growing to 1.5 m tall, with sparsely hairy stems. The leaves
are slender, 2–10 cm long and up to 1 cm broad, with a coarsely toothed margin. The flower
s are produced in dense inflorescence
s 1 cm in diameter, with a ring of white or pale purple ray florets and a centre of yellow disc florets.
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 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.
C. 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. C. canadensis is distinguished by bract
s that have a brownish inner surface and no red dot at the tip, and are almost free of the hairs found on the bracts of the other species.
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
and Central America
Central America
Central America is the central geographic region of the Americas. It is the southernmost, isthmian portion of the North American continent, which connects with South America on the southeast. When considered part of the unified continental model, it is considered a subcontinent...
. Common names include Horseweed, Canadian Horseweed, Canadian Fleabane, Coltstail, Marestail and Butterweed.
It is an annual plant
Annual plant
An annual plant is a plant that usually germinates, flowers, and dies in a year or season. True annuals will only live longer than a year if they are prevented from setting seed...
growing to 1.5 m tall, with sparsely hairy stems. The leaves
Leaf
A leaf is an organ of a vascular plant, as defined in botanical terms, and in particular in plant morphology. Foliage is a mass noun that refers to leaves as a feature of plants....
are slender, 2–10 cm long and up to 1 cm broad, with a coarsely toothed margin. The flower
Flower
A flower, sometimes known as a bloom or blossom, is the reproductive structure found in flowering plants . The biological function of a flower is to effect reproduction, usually by providing a mechanism for the union of sperm with eggs...
s are produced in dense inflorescence
Inflorescence
An inflorescence is a group or cluster of flowers arranged on a stem that is composed of a main branch or a complicated arrangement of branches. Strictly, it is the part of the shoot of seed plants where flowers are formed and which is accordingly modified...
s 1 cm in diameter, with a ring of white or pale purple ray florets and a centre of yellow disc florets.
Horseweed is commonly considered a weed, and in Ohio
Ohio
Ohio is a Midwestern state in the United States. The 34th largest state by area in the U.S.,it is the 7th‑most populous with over 11.5 million residents, containing several major American cities and seven metropolitan areas with populations of 500,000 or more.The state's capital is Columbus...
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
Dicamba
Dicamba is an herbicide. Brand names for formulations of this herbicide include Banvel, Oracle and Vanquish...
in a burndown application prior to planting to control horseweed.
Horseweed 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.
C. canadensis can easily be confused with C. sumatrensis
Conyza sumatrensis
Conyza sumatrensis is an annual herb native to North America but naturalised worldwide.In certain countries the plant has started to exhibit resistance to herbicides....
, which may grow to a height of 2 m, and the more hairy C. bonariensis
Conyza bonariensis
Conyza bonariensis is a species of Conyza, found throughout the tropics and subtropics as a weed; its precise native origin is unknown, but most likely Central America or South America...
which does not exceed 1 m. C. canadensis is distinguished by bract
Bract
In botany, a bract is a modified or specialized leaf, especially one associated with a reproductive structure such as a flower, inflorescence axis, or cone scale. Bracts are often different from foliage leaves. They may be smaller, larger, or of a different color, shape, or texture...
s that have a brownish inner surface and no red dot at the tip, and are almost free of the hairs found on the bracts of the other species.
External links
- canadensis, ITISItisItis may refer to* Integrated Taxonomic Information System, a partnership designed to provide consistent and reliable information on the taxonomy of biological species...
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