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Erigeron canadensis
About Horseweed (Erigeron canadensis) 0 Nurseries Carry This Plant 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. 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. 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).
Plant Description
Plant Type
Plant Type
Annual herb

4.9 ft tall

Flower Color
Flower Color
White, Yellow

Wildlife Supported

Landscaping Information
Common uses
Common uses
Bee Gardens

Natural Setting
Annual Precipitation: 2.7" - 77.2", Summer Precipitation: 0.14" - 2.69", Coldest Month: 30.9" - 59.0", Hottest Month: 57.0" - 88.0", Humidity: 0.45" - 38.66", Elevation: -4" - 6921"

Alternative Names
Common Names: Canadian Horseweed

Sources include: Wikipedia. All text shown in the "About" section of these pages is available under the Creative Commons Attribution-ShareAlike License. Plant observation data provided by the participants of the California Consortia of Herbaria, Sunset information provided by Jepson Flora Project. Propogation from seed information provided by the Santa Barbara Botanical Garden from "Seed Propagation of Native California Plants" by Dara E. Emery. Sources of plant photos include CalPhotos, Wikimedia Commons, and independent plant photographers who have agreed to share their images with Calscape. Other general sources of information include Calflora, CNPS Manual of Vegetation Online, Jepson Flora Project, Las Pilitas, Theodore Payne, Tree of Life, The Xerces Society, and information provided by CNPS volunteer editors, with special thanks to Don Rideout. Climate data used in creation of plant range maps is from PRISM Climate Group, Oregon State University, using 30 year (1981-2010) annual "normals" at an 800 meter spatial resolution.

Links:   Jepson eFlora Taxon Page  CalPhotos  Wikipedia  Calflora

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