Salsola paulsenii
(barbwire Russian thistle)

Pictures

Identity

Preferred Scientific Name

• Salsola paulsenii

Preferred Common Name

• barbwire Russian thistle

International Common Names

• Chinese: chang ci zhu mao cai

Summary of Invasiveness

Russian thistles or tumbleweed of the genus Salsola are annual weeds, mostly native to Europe and Asia, but introduced globally. Salsola infests many tens of millions of hectares, especially in North America. S. paulsenii is a coarse, spiny annual weed native to Central Asia and introduced to North America. It tends to be found in drier and more lowland desert areas in the western USA as compared to other weedy Salsola species, with which it is often confused. S. paulsenii can be controlled by cultivation and chemicals, and a number of biological control agents have been tested. However, it is likely to remain a troublesome weed unless biocontrol eventually offers a viable option.

Taxonomic Tree

• Domain: Eukaryota
•     Kingdom: Plantae
•         Phylum: Spermatophyta
•             Subphylum: Angiospermae
•                 Class: Dicotyledonae
•                     Order: Caryophyllales
•                         Family: Chenopodiaceae
•                             Genus: Salsola
•                                 Species: Salsola paulsenii

Notes on Taxonomy and Nomenclature

The genus Salsola is in the Chenopodiaceae, subfamily Salsoloideae, tribe Salsoleae (USDA-ARS, 2015); however, some authorities place it in the Amaranthaceae family (The Plant List, 2013, Missouri Botanical Gardens, 2015).

No synonyms are recorded for S. paulsenii in the Plant List (2013), but the synonym S. pellucida Litv. is noted in Missouri Botanical Gardens (2015), along with two subspecies, subsp. praecox (Litv.) Rilke, and subsp. oreophila Kinzik. The Plant List recognizes S. pellucida an accepted species.

S. paulsenii is also known as Kali paulsenii (Akhani et al., 2007), based on a major reclassification of the genus that has not been generally accepted. Akhani et al. (2007) split the genus Salsola into five new genera, based on the sections that were raised to the rank of genus. Although these genera are found in the literature, the broader limits of the genus Salsola are still generally accepted. Taxonomic confusion still surrounds many Salsola species.

Akhani et al. (2014) continued to argue that the correct generic name is Kali, describing the origins of the generic names Salsola L. and Kali Mill., and stating that the latter is legitimate name, published independently from Salsola, even though the original generic boundaries are by and large the same. This was countered, however, by Mosyakin et al. (2014), with a proposal to conserve the name Salsola (Chenopodiaceae s.str.; Amaranthaceae sensu APG), with Salsola kali as the conserved type.

Amongst species in Salsola sect. kali, commonly known collectively as the tumbleweeds, S. paulsenii is a relatively distinct species, unlike S. kali, S. tragus, S. australis and others that have a confused taxonomy, with numerous changes in synonomy and species limits.

Even over 40 years ago, Beatley (1973) observed that Russian thistle (S. kali) populations widespread in the western USA appeared to consist of two distinct species: S. paulsenii on disturbed land below 1200 m, especially on limestone-derived soils, and S. iberica, which is abundant on disturbed land above 1800 m, especially on sandy soils of volcanic origin. It was noted, however, that hybridization was frequent, with various degrees of introgression (Beatley, 1973).

Nonetheless, Smith et al. (2013), presented a clear distinction between the exotic and invasive species present in North America, based on recent studies on morphology, allozymes and molecular genetics. These indicated that what is often known as Russian thistle comprises seven distinct species, with S. tragus probably the most widespread, S. collina Pall. mainly east of the Rocky Mountains, S. paulsenii Litv. primarily in deserts, S. kali restricted to ocean shores and is not a rangeland weed, and S. australis R. (sometimes known as ‘type B’) mainly in California, South Africa and Australia; S. australis has never been documented to occur in Eurasia. Polyploid hybrids include S. x gobicola (including S. tragus and S. paulsenii) that is known in western USA and central Asia, and S. x ryanii (including S. tragus and S. australis), known only from California.

Although it was previously believed that all species in the kali section of Salsola originated in Eurasia, the presence of four indigenous species in Australia suggests a separate clade, and it is likely that S. australis is native to Australia. However, other taxonomic listings, such as the Plant List (2013), GRIN (USDA-ARS, 2015) and Tropicos (Missouri Botanical Gardens, 2015) tend to include S. tragus and S. australis and at least some of their noted varieties as synonyms of S. kali.

Using alloenzymes and DNA-based molecular markers, Ryan and Ayres (2000) confirmed the distinction between two accessions of S. tragus [S. kali subsp. tragus] (one from California, USA, and the other from the native range of France and Turkey), and S. paulsenii. Analysis confirmed the genetic distinctness of the two isoenzymic phenotypes of S. tragus, and that S. paulsenii was markedly different from both types. Further analysis (Ayres et al., 2009) reconfirmed as distinct species S. tragus and S. paulsenii, as well as the recently identified S. kali subspecies austroafricana, possibly native to South Africa.

Molecular analyses also identified as an additional taxon a new allopolyploid hybrid between S. tragus and S. kali subsp. austroafricana, and another as a complex hybrid involving S. tragus, S. paulsenii and S. kali subsp. austroafricana.

Description

Adapted from Flora of North America Editorial Committee (2014):

S. paulsenii is a small annual herb, 10-80 cm tall, sometimes to 1 m, glabrous or sparsely papillose to hispid. Stems are erect, rarely ascending or prostrate, and are profusely branched from or near the base, with straight or arcuate branches. Leaves are alternate; the blade filiform to narrowly linear and usually less than 1 mm wide, sometimes to 2 mm wide, fleshy or not, not swollen at base, apex subspinose or spinescent. Inflorescences distinctly interrupted at maturity, 1-flowered (rarely 2-3-flowered with lateral flowers mostly abortive); bracts alternate, not imbricate, strongly reflexed at maturity, base not distinctly swollen, narrowing into spinose apex. Flowers comprised of spreading or reflexed bracteoles, distinct or connate near base, spinescent; perianth segments prominently winged (two wings usually reduced to small, almost subulate winglike appendages, apex long-acuminate or long-subulate and spinose, forming slender columnar beak distal to wings at maturity, glabrous; with the fruiting perianth 7-12 mm in diameter.

Plant Type

Distribution

S. paulsenii is native to a large part of Central Asia, from southern European Russia (Dagestan, Kalmykia, Orenburg, Rostov and Volgograd) to Mongolia and western China (Xinjiang), and from Kazakhstan in the north to Pakistan in the south (USDA-ARS, 2015).

It has been widely introduced, and is especially prevalent in the western USA, particularly California, Oregon, Nevada, Utah, Arizona, Colorado, New Mexico and Texas (USDA-NRCS, 2015). It is likely to be present in many more countries than those listed in the Distribution table, such as Mexico; its distribution is likely to become clearer following taxonomical clarification of the genus. However, it is not reported in Australia (CHAH, 2015), Pacific islands (PIER, 2015) or the Caribbean (Kairo et al., 2003).

Distribution Table

The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.

History of Introduction and Spread

Salsola is thought to have been introduced to North America from Eurasia in the 1800s. S. paulsenii was first reported from North America by Munz (1968), and details of its establishment and early spread, distribution and morphology were discussed by Beatley (1973), Fuller (1986) and Rilke (1999).

For an indication of rates of spread, in six years between 1973 and 1979 the frequency of S. paulsenii in a degraded plant community in Nevada increased from 79% to almost total canopy cover of 98%, whereas the cover of S. iberica disappeared completely, falling from 11% to 0% (Evans and Young, 1980).

Risk of Introduction

S. paulsenii is a declared noxious weed in California (USDA-NRCS, 2015), and closely related Salsola species are declared noxious in many other US states and Canadian provinces. S. paulsenii is adapted to range of dry, cold and temperature climates, and has the potential to invade large areas around the world if it was introduced. No Salsola species should be intentionally introduced to any new areas for any purposes, and care should be taken to reduce any risks of accidental introduction, such as with the movement of hay made from S. paulsenii or hay containing its seeds.

Habitat

In its native range, S. paulsenii is a widespread rangeland and agricultural weed. Where introduced, it is also a rangeland and agricultural weed, especially in sandy soils, disturbed natural and semi-natural plant communities, semi-deserts, deserts, eroded slopes, sand dunes and sandy waste places. Beatley (1973) observed S. paulsenii to be common in western USA on disturbed land below 1200 m, especially on limestone-derived soils. It dominates severely degraded native plant communities in the most arid portions of the Great Basin (western USA) and southwest USA.

Habitat List

Biology and Ecology

Genetics

S. paulsenii is a tetraploid species with a chromosome number reported as 2n = 36 (Zakharyeva, 1985; Wang et al., 2008). Ploidy levels may be a useful means for separating it from some other species of Salsola that are diploid or have higher ploidy levels. Reports of a chromosome number of 2n = 18 for S. paulsenii are probably erroneous and based on misinterpretation of data (Flora of North America Editorial Committee, 2014). Other forms conventionally named as ‘Salsola X’ and ‘S. paulsenii lax form’ with 2n = 54 (e.g. Arnold, 1972; Ryan and Ayres, 2000) are probably of hybrid origin.

Reproductive biology

S. paulsenii reproduces by seed, which can only survive for up to two years in the soil. S. paulsenii seed has temperature related after-ripening requirements, but these are less stringent and break down sooner after maturity than S. kali seed. The shorter after-ripening requirements allow for germination during the winter months, giving S. paulsenii a distinct competitive advantage under arid conditions with winter precipitation and summer drought (Young and Evans, 1979b). S. paulsenii is more suited than S. iberica to arid environments because S. paulsenii can germination at a broader temperature range and sooner after maturity, is more rapid at low temperatures and during the first 10 days of incubation, and because seed dehiscence occurs without the uprooting and tumbling of the plants (Young and Evans, 1979b).

Seed production of S. paulsenii was correlated strongly with herbage yield and weakly with plant density, and was markedly lower than S. iberica (Evans and Young, 1980). Later studies by Evans and Young (1982) on seed germination and seedbed ecology of S. paulsenii and S. iberica confirmed that both exhibited temperature related after-ripening requirements after maturity in autumn and winter, and once requirements has been met both species germinated well at a wide range of temperatures. However, S. paulsenii seeds did not germinate well under very low osmotic potentials. Seedling establishment was increased by soil and litter coverage and by favourable microtopography of the soil surface.

Specific adaptations of S. paulsenii include earlier maturation and seed dispersal, seed dispersal under parent plants, and less specific temperature related after-ripening requirements as compared to S. iberica; but even with these characteristics, S. paulsenii establishment was lower in arid environments compared with S. iberica (Evans and Young, 1982).

Physiology and phenology

Most Salsola species exhibit C4 photosynthesis. Four species from Central Asia were investigated by Pyankov et al. (2000) to determine the structural and functional relationships in photosynthesis of cotyledons compared to leaves, using anatomical and biochemical criteria. These included S. paulsenii from section Salsola, S. richteri from section Coccosalsola, S. laricina from section Caroxylon, and S. gemmascens from section Malpigipila. Results show that all species have a C4 type of photosynthesis in leaves with a Salsoloid type Kranz anatomy, whereas both C3 and C4 types of photosynthesis were found in cotyledons. S. paulsenii (and S. richteri) have NADP- (NADP-ME) C4 type biochemistry with Salsoloid Kranz anatomy in both leaves and cotyledons (Pyankov et al., 2000).

S. paulsenii flowers in spring and summer.

Environmental requirements

S. paulsenii is adapted to range of dry, cold and temperature climates. Native to Central Asia, it can tolerate great extremes in both diurnal and annual temperature, tolerating cold and frost as well as daily highs above 40ºC. The native range is often characterized by low rainfall areas, and it can also tolerate long dry seasons.

Where introduced, it is commonly found in sandy soils, eroded slopes and sand dunes, in dry areas, up to 1900 m altitude. It has been observed that S. paulsenii is similar in ecological requirements to S. kali (Young and Evans, 1979b).

The transport of aqueous-soluble solutes in dust was investigated in Nevada, USA, and it was concluded that increases in potassium, nitrate, ammonium, sulphur and salt content of aeolian dust were likely to be responsible for the invasion of S. paulsenii (Blank et al., 1999).

Climate

Rainfall

Soil Tolerances

Soil drainage

• free

Soil reaction

• acid
• alkaline
• neutral

Soil texture

• light
• medium

Special soil tolerances

• infertile
• saline
• shallow
• sodic

Means of Movement and Dispersal

Natural dispersal

S. paulsenii seeds dehisce and disperse without the plants having to uproot and tumble, as is the case with most forms of S. kali, S. iberica and other species (Young and Evans, 1979b).

Vector transmission (biotic)

In Nevada, S. paulsenii seed was found in the caches of nocturnal, seed-eating rodents of the Heteromyidae family, of which Dipodomys merriami was the main species, and the survival rates of seedlings in caches was significantly higher than that of single seedlings (Longland, 1995). It is thus considered likely that other small mammals as well as other species could be responsible for local dissemination of S. paulsenii seed.

Accidental introduction

Being present in rangeland and pastures, S. paulsenii seed is a potential seed contaminant, especially with the cutting and transportation of hay.

Pathway Causes

Pathway Vectors

Plant Trade

Impact Summary

Economic Impact

S. paulsenii is an important weed in southwestern USA and, along with other Salsola species, the economic impact on agriculture, rangeland management and control in protected areas is likely to be significant.

Risk and Impact Factors

• Invasive in its native range
• Proved invasive outside its native range
• Has a broad native range
• Abundant in its native range
• Highly adaptable to different environments
• Tolerates, or benefits from, cultivation, browsing pressure, mutilation, fire etc
• Pioneering in disturbed areas
• Highly mobile locally
• Fast growing
• Has high reproductive potential
• Has propagules that can remain viable for more than one year
• Has high genetic variability

• Monoculture formation
• Negatively impacts agriculture
• Reduced native biodiversity

• Competition - monopolizing resources
• Rapid growth

• Highly likely to be transported internationally accidentally
• Difficult to identify/detect as a commodity contaminant
• Difficult to identify/detect in the field
• Difficult/costly to control

Uses

Although S. paulsenii, S. iberica and hybrids of the two are aggressive weeds of dry areas in the western USA, they have been used for making hay and silage in bad years with very few reports of ill effects (Fowler et al., 1979). It chemically comparable to many cultivated forages and appears amenable to cultural modification of its nutritive properties, and the considerable variability among intergrades between these species is an advantage.

Uses List

Animal feed, fodder, forage

• Forage

Similarities to Other Species/Conditions

S. paulsenii is similar to S. tragus sensu stricto. Intermediate forms are known, and S. paulsenii × S. tragus hybrids have been identified, identical with S. × gobicola. Forms conventionally named as ‘Salsola X’ and ‘S. paulsenii lax form,’ with 2n = 54 (e.g. Arnold, 1972; Ryan and Ayres, 2000), are probably also of hybrid origin.

S. paulsenii is also noted to be similar in flowers and fruits to S. tragus and S. vermiculata, but it is easily distinguished from them by its shrubby perennial habit and oblong to ovate leaves with round tips (Flora of North America Editorial Committee, 2014). Crompton and Bassett (1985) provided a key that separates the closely related species S. paulsenii, S. kali, S. collina and S. pestifer.

Prevention and Control

Physical/mechanical control

Cultivation can effectively control S. paulsenii, but must be repeated for at least two years until all seeds in the seedbank loose viability, as well as ensuring that no more seeds are re-introduced.

Biological control

The eriophyid mite, Aceria salsolae (Acari: Eriophyidae), was collected in Greece and evaluated for host plant specificity as a prospective biological control agent of invasive alien tumbleweeds in the USA, including S. paulsenii, S. tragus, S. collina and S. australis. The mite does not form galls, but is a vagrant that inhabits leaf and flower bud crevices, and feeding damage stunts the plant. The mite was able to multiply only on species in the Salsola section Kali subsection Kali, which includes the alien weeds Salsola collina, Salsola kali and Salsola paulsenii. It did not damage or multiply on Salsola soda, which is in a different section, nor on Halogeton glomeratus, which is in the same tribe. The mite reduced plant size by 66% at 25 weeks post-infestation under artificial conditions (Smith, 2005). Further studies concluded that there would be no significant risk to non-target plants as a result of using A. salsolae as a biological agent to control Salsola species in North America (Smith et al., 2009).

The search for biological control agents on related species continues, and a recent study found that a gall forming midge, Desertovelum stackelbergi Mamaev from Uzbekistan and a fungal pathogen, Colletotrichum gloeosporoides (Penz) from Hungary had much higher rates of attack and damage to S. tragus than S. australis (Smith et al., 2013). It is also clear that different agents have different impacts on closely related species, and so further work on taxonomic elucidation is required.

Chemical control

Herbicides found to be effective with other Salsola species, especially S. kali and close relatives, are likely to be effective for the control of S. paulsenii.

References

Akhani H; Edwards G; Roalson EH, 2007. Diversification of the old world Salsoleae s.l. (Chenopodiaceae): molecular phylogenetic analysis of nuclear and chloroplast data sets and a revised classification. International Journal of Plant Sciences, 168(6):931-956. http://www.journals.uchicago.edu/IJPS/home.html

Akhani H; Greuter W; Roalson EH, 2014. Notes on the typification and nomenclature of Salsola and Kali (Chenopodiaceae). Taxon, 63(3):647-650. http://www.ingentaconnect.com/content/iapt/tax/2014/00000063/00000003/art00013

Ayres D; Ryan FJ; Grotkopp E; Bailey J; Gaskin J, 2009. Tumbleweed (Salsola, section Kali) species and speciation in California. Biological Invasions, 11(5):1175-1187. http://www.springerlink.com/content/q785758119m43062/?p=4401958f27c2470391b4cef788abbd0b&pi=8

Beatley JC, 1973. Russian thistle (Salsola) species in western United States. Journal of Range Management, 26(3):225-226.

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CHAH (Council of Heads of Australasian Herbaria), 2015. Australia's virtual herbarium. Australia: Council of Heads of Australasian Herbaria. http://avh.ala.org.au

Crompton CW; Bassett IJ, 1985. The biology of Canadian weeds. 65. Salsola pestifer A. Nels. Canadian Journal of Plant Science, 65(2):379-388.

Evans RA; Young JA, 1980. Establishment of barbwire Russian thistle in desert environments. Journal of Range Management, 33(3):169-173.

Evans RA; Young JA, 1982. Russian thistle and barbwire Russian thistle seed and seedbed ecology. Agricultural Research Results, ARS, USDA, No.ARR-W-25. 40pp.

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PIER, 2015. Pacific Islands Ecosystems at Risk. Honolulu, USA: HEAR, University of Hawaii. http://www.hear.org/pier/index.html

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Smith L, 2005. Host plant specificity and potential impact of Aceria salsolae (Acari: Eriophyidae), an agent proposed for biological control of Russian thistle (Salsola tragus). Biological Control, 34(1):83-92. http://www.sciencedirect.com/science/journal/10499644

Smith L; Cristofaro M; Lillo Ede; Monfreda R; Paolini A, 2009. Field assessment of host plant specificity and potential effectiveness of a prospective biological control agent, Aceria salsolae, of Russian thistle, Salsola tragus. Biological Control, 48(3):237-243. http://www.sciencedirect.com/science/journal/10499644

Smith L; Hrusa GF; Gaskin JF, 2013. How many species of Salsola tumbleweeds (Russian thistle) occur in the Western USA? In: Proceedings of the XIII International Symposium on Biological Control of Weeds, Waikoloa, Hawaii, USA, 11-16 September, 2011 [ed. by Wu, Y.\Johnson, T.\Sing, S.\Raghu, S.\Wheeler, G.\Pratt, P.\Warner, K.\Center, T.\Goolsby, J.\Reardon, R.]. Hilo, USA: USDA Forest Service, Pacific Southwest Research Station, Institute of Pacific Islands Forestry, 177.

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Principal Source

Draft datasheet under review

Contributors

30/04/15 Original text by:

Nick Pasiecznik, consultant, France

Distribution Maps