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 bur ragweed, Hooker's bur-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.
- "Ambrosia acanthicarpa". Natural Resources Conservation Service PLANTS Database. USDA. Retrieved 8 January 2016.
- "BSBI List 2007" (xls). Botanical Society of Britain and Ireland. Archived from the original on 2015-02-25. Retrieved 2014-10-17.
- 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.
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