Ambrosia acanthicarpa is a North American species of bristly annual plants in the (sunflower family. Members of the Ambrosia genus are called ragweeds. The species has common names including flatspine burr ragweed, annual burrweed, and annual bur-sage, and western sand-bur. The plant is common across much of the western United States and in the 3 Prairie Provinces of Canada.
This spiny, weedy plant grows in clumps of many erect stems which may reach over a meter in height. Its gray-green stems are covered in a coat of stiff, bristly hairs. The few rough leaves are several centimeters long. The racemes of flowers are more plentiful, with each hairy flower head a few millimeters wide. The spiny, burr-like pistillate heads have pointed, twisting bracts and the staminate heads are rounded. The species is adaptable and grows well in disturbed areas, easily becoming weedy.
- The Plant List Ambrosia acanthicarpa Hook.
- Biota of North America Program 2013 county distribution map
- Great Plains Flora Association. 1986. Flora of the Great Plains i–vii, 1–1392. University Press of Kansas, Lawrence.
- Flora of North America Vol. 21 Page 15 Ambrosia acanthicarpa Hooker, Fl. Bor.-Amer. 1: 309. 1833.
- Jepson Manual Treatment
- United States Department of Agriculture Plants Profile
- Calphotos Photo gallery, University of California
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