BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Salsola kali | Russian-Thistle 



GENERAL BOTANICAL CHARACTERISTICS : 
Russian-thistle is an exotic, annual, erect, xerohalophytic forb
[2,6,34].  It is highly branched and rounded in form, growing from 1 to
3 feet (3-10 m) in height and from 1 to 5 feet (3-17 m) in diameter.
The awl-shaped, spiny-tipped leaves bear small, inconspicuous flowers in
the leaf axils.  The small, winged seed, retained in the leaf axils
until after plant death, contains no endosperm tissue, but is instead
comprised of a spirally-coiled, complete embryo [34] already containing
some chlorophyll [56].  The root system consists of a taproot, reaching
0.3 foot (1 m) or more in depth, and extensive lateral roots.  Under
crowded conditions, roots are shallow [1].


RAUNKIAER LIFE FORM : 
   Therophyte


REGENERATION PROCESSES : 
Russian-thistle is a highly effective reproducer.  After seeds mature in
late fall the plant stem separates from the root [61].  The plant is
then blown by wind.  Seeds, held in the leaf axils, fall to the ground
as the plant tumbles [18].  Further dispersal is accomplished when wind
scatters the winged seeds.  The seed wings may aid in seed germination
by absorbing soil moisture.  One plant typically produces about 250,000
seeds, which remain viable for less than a year [61].  Fresh seed will
germinate at a very limited range of alternating day/night seedbed
temperatures:  68/41 degrees Fahrenheit (50/5 deg C) [62].  Over winter,
temperature restrictions disappear.  In spring, Russian thistle seeds
will germinate at virtually any conceivable seedbed temperature,
including alternating day/night temperatures of 122/29 degrees
Fahrenheit (50/-2 deg C) [63].  In tests conducted in a big sagebrush
community in Nevada, Evans and Young [23] noted the following
germination percentages at various nighttime minimum temperatures:

     Temperature (deg C)    Germination (%)    
           -3                     0               
            0                    26              
            3                    43               
            5                    56             
            7                    88            
            9                    78
           10                    88
           15                    78
           20                    66
           25                    29

At optimum temperatures (44 to 50 degrees Fahrenheit [7-10 deg C]),
germination is accomplished within minutes [55].  This extremely short
germination time aids in establishment in desert environments.
Germination is epigeal or hypogeal [63].  The spirally-coiled embryo
unwinds and pushes the root into the soil.  Embryos do not survive if
they germinate on compacted soil, or at a soil depth of greater then 5
inches (13 cm) [55].  Russian-thistle seedlings are poor competitors,
and do not establish well in crowded communities [61].


SITE CHARACTERISTICS : 
Russian-thistle grows in disturbed or unoccupied sites at elevations
from below sea level (in Death Valley, California) to 8,550 feet (2,606
m) [61].  It grows in any type of well-drained, uncompacted soil with a
sunny exposure [55,61].  It is most frequent, however, in alkaline or
saline soils due to reduced competition.  Russian-thistle cannot
tolerate saturated soil for extended periods of time [61].


SUCCESSIONAL STATUS : 
Obligate Intitial Community Species

Russian-thistle is a shade-intolerant initial colonizer in primary and
secondary succession.  It colonizes barren desert areas that cannot
support other flora [61], and invades many different disturbed plant
communities [9].  In disturbed big sagebrush communities,
Russian-thistle dominates for the first 2 years.  After this time plants
become overcrowded and stunted [49] and are often replaced by mustards
(Descurainia and Sisymbrium spp.)  [46].


SEASONAL DEVELOPMENT : 
The following seasonal development has been reported for
Russian-thistle:

     germinates:  late April - August [62]
     flowers:  June - August [31,34,61]
     seeds mature:  August - November [42,61]
     plant dies:  first fall frost [10,31]
     seeds disseminate:  late fall [10,61]
     

Related categories for Species: Salsola kali | Russian-Thistle