|K.. tragus in tumbleweed mode|
Salsola kali L. subsp. tragus
Kali tragus is a species of flowering plant in the family Amaranthaceae. It is known by various common names such as Russian thistle or tumbleweed, the latter because it is the commonest species of tumbleweed in many regions of the United States. Informally it also is known as "Salsola", which was its generic name until fairly recently.
Origin and distribution
Kali tragus is native to Eurasia but in the 1870s it appeared in South Dakota when flaxseed from Russia turned out to be contaminated with Kali seeds. It proved to be highly invasive as an introduced species and rapidly became a common ruderal weed of disturbed habitats in many regions of North America, particularly in the Midwest. It also has become naturalized in various regions of Central and South America and in parts of southern Africa and Australia. It now occupies a wide variety of habitat types and often is the first or even the only colonizer where no local species can compete successfully.
Kali tragus is an annual forb. In habit the young plant is erect, but it grows into a rounded clump of branched, tangled stems, each one typically about a metre long. Depending on the plant's genetics and condition, the leaves and stems may be green, red, or striped, and they may be hairless or pubescent. The leaves are tipped with spines that in most varieties are so sharp that the plants are best handled with gloves and other suitably protective clothing, though some genetic variants have only a hair at the tip. On the young plant leaves may be more than 5 cm long, succulent and more or less cylindrical; these juvenile leaves are deciduous and drop off as the plant matures. The leaves of the mature plant are persistent, leathery, broader and shorter than the young leaves (seldom more than 1 cm in length), rigid and spine-tipped. They remain on the stem till the plant dies at the end of the season. In the axil of the mature leaf there are two leaf-like bracts with a flower between them. The flower lacks petals, but is surrounded by a disk of wide, winged sepals, whitish to pink in color.
Reproduction and dispersal
A large specimen of Kali tragus may produce 200,000 seeds.
The plant becomes woody as the fruits develop. As they approach maturity it begins to die, dries out, becomes brittle, and readily breaks off at the base of the stem. Once that happens it readily rolls before the wind and disperses its seeds as a tumbleweed.
Ecology and agricultural significance
Kali tragus is a ruderal annual forb. It germinates rapidly even in very small amounts of moisture in arid conditions, when young it may be grazed, but that phase lasts for only a brief period, and generally at a time when other forage is relatively plentiful. After this it becomes a weed in most contexts. To begin with, as it matures it becomes too spiny and woody for for most stock to browse. As its fruits mature, the plant dies, dries and becomes brittle. It is in this state that it is likely to detach from its root and become a tumbleweed. As tumbleweeds go, it is very large, a metre or more in diameter, spiny, largely inedible, and fire hazard.
- Hossein Akhani, Gerald Edwards, Eric H. Roalson:Diversification Of The Old World Salsoleae s.l. (Chenopodiaceae): Molecular Phylogenetic Analysis Of Nuclear And Chloroplast Data Sets And A Revised Classification In: International Journal of Plant Sciences 168(6), 2007: 931–956
- Flora of North America
- Starr, F., K. Starr, and L. Loope.Salsola tragus in Hawaii. USGS. 2003.
- Shinn, C. H. The Russian Thistle in California. University of California Agricultural Experiment Station. Berkeley, May 1895. [ucanr.edu/repository/fileaccess.cfm?article=101707&p=BEMUBT]
|Wikimedia Commons has media related to Kali tragus.|
- Jepson Manual Treatment - Kali tragus
- USDA Plants Profile: Salsola tragus (Russian thistle)
- Washington Burke Museum - Salsola tragus
- Salsola tragus - U.C. Photo gallery
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