Salsola tragus, often known by its synonym , 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 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, 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 ; it is native to Eurasia, but in the 1870s, it appeared in South Dakota when flaxseed from Russia turned out to be contaminated with 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 and in America. Recent studies show that the population once assigned to 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 and – have since been included in the Amaranthaceae. They now are allocated to the Salsoloideae, a subfamily of the Amaranthaceae.
Description
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 may produce some 200,000 seeds.
Invasive potential 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
is a ruderal annual forb. It germinates rapidly even with very little moisture in arid conditions. When young, it may be grazed freely, 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. One reason is that as they mature, most varieties become too spiny and woody for most stock to browse. Moreover, older foliage develops higher levels of oxalates, bitter tannins, and alkaloids, making it unpalatable. As its fruits mature, the plant dies, dries, and becomes hard and brittle. In this state, it is likely to detach from its root and become a tumbleweed. As tumbleweeds go, it is very large, often a metre or more in diameter, spiny, largely inedible to most livestock if unprocessed, and a fire hazard.; and However, in regions where there is plentiful winter rain, the moisture softens both the twigs and the spines, after which hardy breeds of livestock and some wildlife species once again will eat it.
has acquired a bad reputation for its spininess, its woodiness in maturity, and its general ecological competitiveness, augmented by its tumbleweed nature, which enables it to spread rapidly across open ground. Prince Gallitzin reported that on the journey out of his native Russia, he passed through southwest Siberia and found the Imperial government's irrigation project abandoned and the farms deserted, on account of K. tragus. Furthermore, Oryol Oblast and Kyiv Oblast were also especially infested. During the past century or more, the majority of the publications that dealt with the topic have discussed its pernicious nature, the increasing threats that the species poses, and how to combat its invasiveness; they largely have ignored its other attributes.
However, even early publications conceded that the plant is of value as forage in severely arid conditions where few other forage species are viable. As for its harmful competitiveness, most authors emphasised its invasiveness, though some did mention its value in regenerating overgrazed or otherwise abused land.
Apart from its value to domestic cattle and sheep in some regions, provides food and shelter for several wildlife species. Its nutritional value is high; it is rich in various minerals, Vitamin A, and phosphorus. It is a minor forage component for bison, mule deer, and wapiti. Pronghorn eat it with reluctance in drought conditions, but feed on it avidly under rainy conditions, especially in wet years. Prairie dogs consume it as a major food wherever they encounter it. Seed-eating birds and small mammals, such as rodents, feed on seeds.
offers shelter for some wildlife. Medium-sized deer species make some use of it, but it is mainly of value to small mammals and bird species that normally live close to the ground and shelter under bushes.
Some livestock species, such as camels and some breeds of stock that are adapted to semi-desert conditions, will brave the spines when forage becomes scarce. Many goats and some breeds of sheep such as karakul browse the bushes. The plant, like many members of the Amaranthaceae, is rich in high-quality proteins with a good balance of essential amino acids, the seed even more so.
Oxalic acid occurs in a wide range of plants, including S. tragus, as an adaptation to alkaline, relatively drier soils rich in calcite, gypsum, alumina, and/or other metal ions. Oxalic acid forms highly insoluble salts with calcium, aluminum, chromium, copper, lead, and many other transition metals. Oxalic acid is produced in specialized parenchyma cells called idioblasts. There it binds with excess calcium from plant tissue, forming needle-like crystals of calcium oxalate monohydrate inside such cells, called raphides. Calcium, along with other metal ions, is sequestered in idioblast cells, reducing its impact on the rest of the plant's tissues. Rhaphides also serve as a deterrent against insect predators, as the sharp crystals injure an insect's digestive tract.
and many related species, including some that are widely regarded as invasive weeds in other countries, are valued in their regions of origin. They are adapted to inhospitable environments that do not support many other forage species. In Uzbekistan, for example, stems, fruits, and leaves are nutritious year-round camel feed; sheep and goats prefer it in summer, but also to some extent in autumn and winter. The fruits are important for fattening camels, goats, and karakul sheep; the fruit may partially substitute for concentrates, especially in autumn and winter. In those regions, annual species are known as "solyanki"; they are important as drought- and salt-tolerant forage and form a dominant group in the flora and vegetation of the most challenging environments. Some are useful for stabilising shifting sands and for the rehabilitation of degraded rangelands, such as the saline soils of the red desert of Kyzyl Kum. Some of the species also invade ruderal sites or occur as weeds in cultivated fields.
Although has not yet received much recognition in contemporary first-world livestock nutrition, this might reflect short memories rather than a lack of evidence for its merits; during the Dust Bowl era, it was credited with rescuing beef cattle husbandry in North America. The usual hay crops had failed, and when all other sources failed, farmers fed their cattle on tumbleweed.
Salsola management and soil rehabilitation