Carnegiea gigantea, Giant Saguaro

Southwest Desert Flora

Home to the plants of the Sonoran, Chihuahuan and Mojave Deserts

Cirsium ochrocentrum, Yellowspine Thistle

Conyza canadensis, Canadian Horseweed

Conyza canadensis, Canadian Horseweed, Southwest Desert Flora Conyza canadensis, Canadian Horseweed, Southwest Desert Flora Conyza canadensis, Canadian Horseweed, Southwest Desert Flora     Conyza canadensis, Canadian Horseweed, Southwest Desert Flora Conyza canadensis, Canadian Horseweed, Southwest Desert Flora     Conyza canadensis, Canadian Horseweed, Southwest Desert Flora

Scientific Name: Conyza canadensis
Common Name: Canadian Horseweed
Also called: Horseweed Fleabane, Horseweed and Mares Tail (Spanish: Cola de Zorra, Jarilla, Cola de Caballo, Hierba del Caballo)
Family: Asteraceae, Sunflower Family
Synonyms: (Erigeron canadensis)
Status: Native
Duration: Annual or perennial.
Size: Up to 5 feet.
Growth Form: Shrub; tall, erect, rigid stem with long white hairs, branches grow out horizontally and upward with numerous flower heads.
Leaves: Green; alternate around the stem but not whorled, numerous leaves, lower leaves oblanceolate to linear, 3 to 4 inches long, bend downward, entire or toothed, upper leaves smaller, sessile.
Flower Color: White or cream; yellow disk flowers, ray flowers with tiny florets, flower heads small, flowering branches spread out in open dense arrays; fruit is an achene with tufts of white or brown hairs, seeds wind dispersed.
Flowering Season: July to October.
Elevation: 1,000 to 7,000 feet.
Habitat Preferences: Variety of habitats, upper and lower deserts, chaparral, pinyon-juniper, disturbed areas, irrigated crop lands, roadsides.
Recorded Range: Found throughout the United States, Canada, Baja California and north and central Mexico. Introduced in AK and Hi. Throughout all of Arizona.

U.S. Weed Information: Conyza canadensis is listed in: Weeds of Kentucky and adjacent states: a field guide, Weeds of the Northeast, Weeds of Nebraska and the Great Plains, Weeds of the United States and Canada, and Weeds of the West. Plants included here may become weedy or invasive.
Invasive/Noxious Weed Information: No data available.
Wetland Indicator: Conyza canadensis is on the USDA 2012 National Wetland Plant List.
Threatened/Endangered Information: The state of Indiana, Division of Nature Preserves, 2002, Endangered, threatened, and rare vascular plant species documented from Indiana lists Conyza canadensis var. pusilla, Fleabane as Extirpated.

Genus Information: 6 species in Conyza throughout North America. 2 species are found in Arizona. There are 3 varieties of Conyza canadensis;
Conyza canadensis var. canadensis, Canadian Horseweed,
Conyza canadensis var. glabrata, Canadian Horseweed and
Conyza canadensis var. glabrata, Canadian Horseweed.

Comments: Canadian Horseweed in a common plant quite unattractive in appearance and weedy by its habitat preferences for disturbed or waste lands and often in open barren areas. Horseweed has minimal wildlife value except for the wide variety of insects they seem to attract.

Multiple ethno-botanical uses have been identified such as for sunburn control, chronic diarrhea and a decoction of the roots and leaves taken for stomach pain. See full species account from Native American Ethnobotany, University of Michigan, Dearborn.

Date Profile Completed: 6/28/2012; Updated, 07/25/2015
References:
U.S. Dept. of Agriculture, Natural Resources Conservation Service on-line database
Arizona Flora, Kearney, Thomas H., Peebles, Robert H., 1960, University of California Press, Berkley and Los Angeles, as Erigeron canadensis.
The Jepson Manual, Citation: http://ucjeps.berkeley.edu/interchange/I_treat_indexes.html, Thu Jun 28 09:44:36 2012
John L. Strother, FNA | Family List | FNA Vol. 20 | Asteraceae | Conyza, Flora of North America Editorial Committee, eds. 1993+. Flora of North America North of Mexico. 16+ vols. New York and Oxford. (accessed 06/28/2012)
SEINet for synonyms, scientific names and recorded geographic locations, http://swbiodiversity.org/seinet/
US Weed Info, KY - Haragan, P.D. 1991. Weeds of Kentucky and adjacent states: a field guide. The University Press of Kentucky. Lexington, Kentucky.
N'EAST - Uva, R.H., J.C. Neal, & J.M. DiTomaso. 1997. Weeds of the Northeast. Cornell University Press. Ithaca, New York.
NE&GP - Stubbendieck, J., G.Y. Friisoe, & M.R. Bolick. 1994. Weeds of Nebraska and the Great Plains. Nebraska Department of Agriculture, Bureau of Plant Industry. Lincoln, Nebraska.
SWSS - Southern Weed Science Society. 1998. Weeds of the United States and Canada. CD-ROM. Southern Weed Science Society. Champaign, Illinois.
WSWS - Whitson, T.D. (ed.) et al. 1996. Weeds of the West. Western Society of Weed Science in cooperation with Cooperative Extension Services, University of Wyoming. Laramie, Wyoming.
T&E info - Indiana: Conyza canadensis var. pusilla – fleabane – Extirpated