tumbleweed, any of several plants, particularly abundant in prairie and steppe regions, that commonly break from their roots at maturity and, drying into a rounded tangle of light, stiff branches, roll before the wind, covering long distances and scattering seed as they go. The Russian thistle—Salsola tragus or Kali tragus of the family Chenopodiaceae (goosefoot family) and not a thistle—is one of the most frequent of the tumbleweeds. Naturalized from Asia, it has become a troublesome pest on Western prairies, although in drought years it may serve as forage in the spring before the spines form. Other Salsola species are also tumbleweeds. Some other common tumbleweeds, such as Amaranthus albus or A. graecizans, are members of the family Amaranthaceae (amaranth family), naturalized from tropical America and now common weed pests in Western agricultural fields. Others are the hedge mustards (species of Sisymbrium) and several other plants of the goosefoot family, e.g., the winged pigweeds (Cycloloma) and the bugseeds (Corispermum). Tumbleweeds of the family Chenopodiaceae and Amaranthaceae are classified in the division Magnoliophyta, class Magnoliopsida, order Caryophyllales.
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