Salsola collina
Salsola tragus
slender Russian-thistle, slender saltwort, tumbleweed
prickly Russian thistle, prickly saltwort, Russian-thistle, soude roulante, southern Russian thistle, tumbleweed
erect, rarely ascending, branched above base (occasionally with slender branches near base);
branches straight or slightly arcuate.
erect, rarely ascending, profusely branched from or near base (rarely simple in underdeveloped specimens);
branches arcuate, proximal ones occasionally ± prostrate.
alternate;
blade filiform to narrowly linear, 1–2 mm wide, less than 1 mm wide in herbarium specimens, usually not fleshy, sometimes semi-amplexicaul at base, apex with soft bristle (rarely subspinescent).
alternate;
blade filiform or narrowly linear, less than 1 mm wide in herbarium specimens, not fleshy, not swollen at base, apex subspinescent (spine less than 1.5 mm).
not interrupted, dense, 1-flowered (rarely 2–3-flowered), often also in axils of proximal leaves and branches, lower ones tightly enclosed in bracts and bracteoles, forming gall-like caducous balls at maturity;
bracts alternate, strongly imbricate and appressed at maturity, base not distinctly swollen, apex acuminate into subulate spine.
interrupted at maturity (at least proximally), 1-flowered (rarely 2–3-flowered with lateral flowers mostly abortive);
bracts alternate at maturity, not imbricate, reflexed, not distinctly swollen at base, ± abruptly narrowing into mucronulate-spinose apex.
bracteoles becoming connate basally and adnate to perianth segments;
perianth segments wingless or with narrow, erose wing at maturity, apex acute, weak and flaccid, glabrous; fruiting perianth ca. 2–5 mm diam. 2n = 18.
bracteoles distinct or occasionally connate at base in proximal flowers;
perianth segments with prominent, membranous wing at maturity (two inner wings usually much smaller than the other three), apex weak, obtuse to weakly acuminate or reflexed, glabrous; fruiting perianth ca. 4–10 mm diam. 2n = 36.
Salsola collina
Salsola tragus
Salsola collina was reported for the first time for North America from Minnesota by J. W. Moore (1938). It was collected in Kansas in 1923 (R. E. Brooks et al. 1976), but misidentified. Later it was discovered in Colorado, Iowa, and Missouri (V. L. Cory 1948; W. Schapaugh 1958; V. Muhlenbach 1979). Reports of S. collina for Arizona and New York are based on specimens cited by S. Rilke (1999). Its actual distribution seems to be underestimated due to the common and constant confusion with deviant forms of S. tragus. In the future, S. collina may be expected to occur within the major portion of the present range of S. tragus.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Salsola tragus probably was introduced to South Dakota in 1870 or 1874 in flaxseed imported from Russia (J. C. Beatley 1973c; C. W. Crompton and I. J. Bassett 1985; S. L. Mosyakin 1996). Now this noxious weed occupies almost all of its potential range in North America. It seems, however, to be quite rare in the southeastern part of the United States.
Salsola tragus has been known in North American and European botanical literature under numerous names (for detailed synonymy see S. L. Mosyakin 1996 and S. Rilke 1999). Judging from the photographs of the Linnaean specimen of S. tragus (LINN 315.3), which should be regarded as a lectotype, it is the correct name for the widespread, narrow-leaved, weedy representative of the S. kali aggregate (Á. Degen 1936–1938, vol. 2; N. N. Tzvelev 1993; S. L. Mosyakin 1996; S. Rilke 1999).
In the present circumscription, Salsola tragus is an extremely polymorphic species consisting of several more or less distinct races (subspecies or segregate species). Several varieties may be recognized within S. tragus, many of them are just morphological variants of little or no taxonomic value.
Studies using allozymes and DNA-based molecular markers in some North American and Eurasian representatives of Salsola tragus indicate that there are at least two cryptic genetically divergent populations (F. J. Ryan and D. R. Ayres 2000). More studies may clarify distribution, origin, and taxonomic status of these infraspecific taxa (or cryptic species).
In spite of being a noxious weed, Salsola tragus is an additional forage source for livestock in arid rangelands. The mature plant may break off at the stem base to form a tumbleweed.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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