Ambrosia acanthicarpa
 Ambrosia acanthicarpa is a species of ragweed known by the common names flatspine burr ragweed annual burrweed and annual bur-sage. 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.