# Salsola tragus

**Chenopodiaceae**

**Russian thistle, tumbleweed**

*Salsola tragus* is an annual herb with glabrous to short stiff hairs.
Stems are generally branched and glabrous. Leaves are 8-52 mm in length
and are threadlike, becoming rigid. The bracts of inflorescences are
subcylindric and spiny. This species is found naturally in more or less
saline, littoral habitats along the Mediterranean Sea (Rilke and Reimann
1996). In California, this introduced weed is common in disturbed places
below 2700 m. The California Exotic Pest council (1995) included *S.
tragus* as a \"List 2\" species, indicating that it is a wildland weed
of secondary importance because it consists of localized populations in
early stages of invasion that lack the ability to dominate native
communities. *S. tragus* is generally considered to be a subspecies of
the widespread European halophyte *Salsola kali*, though the taxonomic
relationships between recognized subspecies is complicated by the
extreme polymorphism within this group. The characters used in major
studies of the taxonomy of this group have included habitat, shape,
thickness of leaves and bracts, color, indument, tepal lobes, and wings
(Allen 1968). The morphological variation observed within this section
of the genus *Salsola* is possible associated with salinity levels.
Teimann and Brecher (1995) and Rilke and Reimann (1996) reported
increasing succulence as a consequence of salt treatments in *S.
tragus*. Recent controlled growth studies of all three subspecies of *S.
kali* indicate that while they are ecologically differentiated in
Europe, morphological variation in growth form, prickliness, and
succulence are obscured by considerable habitat induced and phenological
variation. Until recently, *S. kali* tragus has been differentiated from
*S.k. iberica* by its succulent leaves, glabrous stems and fruits
without wings. The results of experiments by Rilke and Reimann (1996)
however, invalidate this differentiation, except for the leaf character,
and in general, these authors question the status of subspecies within
*S. kali*. Onal (1969) showed in laboratory experiments that accessions
of *S. kali* tragus grew better in moderately saline (0.5% NaCl) water,
while Eschel (1985) found that in sand grown plants 1.50 mmol/l NaCl
doubled the fresh weight of ssp. tragus. These authors conclude that *S.
kali* tragus is the most salt tolerant subspecies of *S. kali* (Reimann
and Breckle 1995).

In the United States, *S. tragus* is an important nonmycotropic
colonizing species in semiarid lands and may influence the abundance of
later seral species (Allen and Knight 1984, Allen 1992). During primary
succession on a windy ridge top in Wyoming, grass density was highest
where *S. kali* was most abundant, indicating thatI S. kali plays a
facultative role in succession at this site. Facilitation may be due to
reduced wind speeds or snow accumulation acting on the grass seedlings.
This facilitation effect might become competitive in late summer, and
future work is needed to sort out the relative effects of these two
processes (Allen and Allen 1988). Previous hypotheses of succession
indicated that an increased innoculum density would hasten the rate of
succession by making later seral species more competitive with early,
seral, nonmycotropic species (Reeves et al. 1979, Allen and Allen 1984).
However, where facilitation, rather than competition, drives succession,
myccorhizal fungi may have a different role. Myccorhizal inoculations
led to lower densities of *S. kali*, but no impact on myccorhizal
grasses. This had an apparent detrimental effect on succession at this
site (Allen and Allen 1988). *S. tragus* may also facilitate
colonization by adding oxalate leachate to the soil. Cannon et al.
(1995) found that leachate derived from *S. tragus* solubilized P from
that inorganic-bound soil P pool, making this P available to colonizing
plants.

A recent study by barrows (1997) indicates that *S. tragus* is a
positive component of the habitat of the threatened Coachella Valley
fringe-toed lizard (Uta inornata). Because it is a non-native species,
managers have expressed concern over the effects of *S. tragus* on this
lizard species. The data presented by barrows, however, show that *S.
tragus* is similar in appearance and microhabitat distribution as native
species used by U. inornata for shading, though *S. tragus* does not
provide a food source for the lizards, as native species do.

**References**

Allen, E.B. 1992. Evaluating community level processes to determine
reclamation success. In: Chambers, J.C., and G.L. Wade (eds). Evaluating
reclamation success: the ecological considerations: proceedings of a
symposium. Northeastern For. Serv. Expt. Sta. Gen. Tech. Rep. NE-164.

Allen, E.B. and M.F. Allen. 1984. Competition netween plants of
different successionAL stages: mycorrhizae as regulators. Can. J. Bot.
62: 2625-2629.

Allen E.B., and M.F. Allen 1988. Facilitation of succession by the
nonmycotropic colonizer *Salsola kali* (Chenopodiaceae) on a harsh site:
effects of myccorhizal fungi. Amer. J. Bot. 75: 257-266.

Allen, E.B. and D.H. Knight. 1984. The effects of introduced annuals of
secondary succession in sagebrush grassland. Southwest Naturalist
29:407-421.

Barrows, C.S. 1997. Habitat relationships of the Coachella Valley
fringe-toed lizard (*Uma inornata*).

Cannon, J.P. E.B. Allen, M.F. Allen. L.M. Dudley, and I.J. Jirimack.
1995. The effects of oxalates produced by *Salsola tragus* on the
phosphoprous nutrition of *Stipa pulchra*. Oecologia 102: 265-272.

Onal, M. 1969. Der Einflub des Natriumchlorids auf das Wachstun einiger
Halophyten. Revuew de la Faculte des Sciences de l\'University
d\'Istanbul. Serie B 34:313-326.

Reimann, C. and S.W. Breckle. 1995. Salt tolerance and ion relations of
*Salsola kali* L.: differences between ssp. *tragus* (L.) nyman and ssp.
ruthenica (iljin.) Soo. New Phytol 130: 37-45.

Rilke, S. and C. Reimann. 1996. Morphological and ecophysiological
differences between the subspecies of *Salsola kali* L. In Europe:
results of culture experiments. Flora 191: 363-376.