A rounded, bushy, much branched annual. 1/2 to 3 feet tall, reproducing by seed. Stems are usually red or purple striped. Leaves are alternate; the first are long, string-like and soft, with later leaves short, scale-liked and tipped with a stiff spine. Inconspicuous green flowers are borne in axils of upper leaves, each flower accompanied by a pair of spiny bracts.
Seeds are spread as mature plants break off at ground level and are scattered by the wind as tumbleweeds. Rapid germination and seeding establishment occur after only a brief and limited amounts of precipitation. Since Russian thistle was introduced (from Russia) in the late 1800's, it has become one of the most common and troublesome weeds in the drier regions of the U.S. It is well adapted to cultivated dry land agriculture, but is also found on disturbed wastelands, overgrazed rangeland, and even some irrigated cropland. Barbwire Russian thistle (S. paulsenii Litv.) is a similar in overall appearance but is generally more course and robust, with broader and more rigid spine-tipped leaves.
Russian thistle synonyms include:
S. kali L., S. kali L. var. tenuifolia Tausch, S. kali L. var. ruthenica (Iljin) Soo, and S. pesitfer A. Nels. |
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