Salsola tragus, often known by its synonym Kali tragus, is a species of flowering plant in the family Amaranthaceae. It is known by various common names such as prickly Russian thistle, windwitch, or common saltwort. It is widely known simply as tumbleweed because, in many regions of the United States, it is the most common and most conspicuous plant species that produces tumbleweeds. Informally, it may be known as Kali or Salsola: the latter being its restored genus, containing 54 other species, into which the obsolete genus Kali has been subsumed. For a brief period during its youth, it may be grazed, but afterward it becomes too spiny and woody to be edible for most wildlife and livestock (unless processed first). Mature specimens are often more than a meter in diameter. As its fruits mature, the diaspore of the plant dies, dries, hardens, and detaches from its root. This detached anatomical part of Salsola tragus is colloquially called "tumbleweed" (although there are many other plant species that also produce tumbleweeds). Once mature, dry, and detached from the plant, this tumbleweed will tumble (i.e., roll) due to the force of the wind. As this dead structure tumbles in the wind, it gradually degrades and falls apart, thereby spreading possibly as many as 200,000 seeds. If it comes to rest in a wet area, it can germinate rapidly, even with very little moisture. It has a high salinity tolerance. It can successfully compete with many native plants in certain environments, such as along seashores and especially in grasslands, deserts, or semiarid regions. Consequently, it now occupies a wide variety of habitats. Native to Eurasia, Salsola tragus has proven to be highly invasive as an introduced species and rapidly became a common ruderal weed of disturbed habitats throughout the world. The tumbleweed's tumbling is known to damage non-native plants and environments, and its highly flammable nature also sometimes helps wildfires spread, especially during windy conditions. An ignited tumbleweed may spread a fire across firebreaks and may even ignite buildings or structures that it stops against.
Taxonomy Linnaeus originally described the species as Salsola tragus; it is native to Eurasia, but in the 1870s, it appeared in South Dakota when flaxseed from Russia turned out to be contaminated with Salsola seeds. Although it is the best-known of this group of weeds and was once thought to be a single, well-defined species, it is now known to include more than one species and some hybrids. This has led to taxonomic confusion in dealing with species in the genera Salsola and Kali in America. Recent studies show that the population once assigned to Salsola tragus comprises three or more morphologically similar species that differ in flower size and shape. The group was widely assigned to the family Chenopodiaceae, but the Chenopodiaceae – including the genera Kali and Salsola – have since been included in the Amaranthaceae. They now are allocated to the Salsoloideae, a subfamily of the Amaranthaceae.
Description
Salsola 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 up to 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.
Ecology
Reproduction and dispersal
The plant becomes woody as the fruits develop. As they ripen, the plant begins to die, dry out, and become brittle. In that state, the base of the stem breaks off easily, particularly in high winds. The plant then rolls readily before the wind and disperses its seeds as a tumbleweed. A large specimen of Salsola tragus may produce some 200,000 seeds.
Invasive potential Salsola tragus has proven 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. The species has also 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 in those regions. It often is the first or even the only colonizer in conditions where no local species can compete successfully. Because it prefers sand and its tolerance of salinity, it commonly grows along sea beaches as well as in disturbed grassland and desert communities, especially in semiarid regions.
Edibility
The plant is edible when young, and its shoots can be harvested and eaten. As the plant matures, it becomes too woody, bitter, and spiny to be considered edible. The young shoots can be eaten raw in salads, and are reported to be even more flavorful when cooked as a pot herb. Young plants are also reported as good fodder for livestock. Some varieties of Russian thistle can contain above-average levels of oxalic acid, particularly in older plants, and people who are sensitive to oxalic acid should avoid the genus, as it is a severe allergen for some. Oxalates in certain vegetables contribute to gout and are a causative agent in certain types of kidney and bladder stones; therefore, K. tragus is not recommended for people with a history of such conditions or with diabetic kidney disease. People who have adverse reactions to eating spinach, which also can have high levels of oxalates, should avoid consumption of Russian thistle.
Ecology and agricultural management
… excerpt ends here. Continue reading the full article.
