Salsola tragus (*)
Salsola tragus L.
* Cent. pl. II::13. 1756 (Amoen. acad. 4:310. 1759)
Salsola tragus is a species of flowering plant in the amaranth family known by the common name prickly Russian thistle, or simply Russian thistle. It is perhaps the most common species of tumbleweed, and may be known by this general name. This plant is native to Eurasia but it has long been present in North America as an introduced species and a common weed of disturbed habitat; it is also naturalized throughout Central and South America and in parts of southern Africa and Australia. It was probably first introduced to the United States when a shipment of flaxseed from Russia was contaminated with its seed and delivered to South Dakota. It now occupies a great number of habitat types.
This is an annual herb forming a rounded, brambly clump of intricately branched, erect, curving stems growing up to a meter long. The green to red stems are hairless to hairy. They are lined with rigid, leathery, needlelike, spine-tipped leaves up to 5 centimeters long. The inflorescence is an interrupted series of flowers, with one flower and a spiny bract per leaf axil. The flower is surrounded by a disclike array of wide, winged sepals which are whitish to bright pink in color. A large plant can produce 100,000 minute seeds.
The plant dries out as the fruits develop, then breaks off at the base of the stem and is carried about by the wind, the dry fruits and seeds dropping off as it rolls. This is the plant's method of biological dispersal.
1. ^ a b Flora of North America
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