ARS | Publication request: How many species of Salsola tumbleweeds (Russian thistle) occur in the Western USA?

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: September 11, 2011
Publication Date: N/A

Technical Abstract: Russian thistle or common tumbleweed, Salsola tragus (sensu lato), is an alien weedy annual plant that infests over 41 million hectares in the western United States. The taxonomy of this plant has had a long confusing history, with frequent misapplication of the species names kali and australis. Recent studies based on morphology, allozymes and molecular genetics indicate that "Russian thistle" comprises seven distinct species in North America. Salsola tragus is probably the most widespread species. Salsola collina occurs primarily east of the Rocky Mountains, S. paulsenii primarily in deserts, and S. kali is restricted to ocean shores and is not a rangeland weed. Salsola australis, sometimes reported as "type B", occurs primarily in California, South Africa and Australia, but has never been documented to occur in Eurasia. Almost all uses of this name before 2008 are probably misapplications. Polyploid hybrids include S. x gobicola (includes S. tragus and S. paulsenii ancestry), which is known from western USA and central Asia, and S. x ryanii (includes S. tragus and S. australis ancestry), which is known only from California. A gall forming midge, Desertovelum stackelbergi, from Uzbekistan (Sobhian et al. 2003. Biol. Control 28: 222-228) and a fungal pathogen, Colletotrichum gloeosporoides, from Hungary (Bruckart et al. 2004. Biol. Control 30: 306-311) had much higher rates of attack and damage to S. tragus than S. australis. Although it was previously believed that all species in the kali section of Salsola originated in Eurasia, the presence of 4 indigenous species in Australia suggests a separate clade (Borger et al. 2008. Aust. J. Bot. 56: 600–608). It is likely that S. australis is native to Australia.