BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Sisymbrium altissimum | Tumblemustard 



GENERAL BOTANICAL CHARACTERISTICS : 
Tumblemustard is an erect, rather freely branched, tall, weedy,
herbaceous annual or biennial that typically ranges in height from 11.7
to 58.5 inches (3-15 dm).  The lower leaves are large and deeply
divided; upper leaves are much reduced.  The root system consists of a
short taproot and poorly developed lateral roots [20].  At maturity the
stem frequently breaks off, allowing the aerial portion to be blown
about by the wind [11,24,25].  Plants are moderately resistant to
trampling by livestock [5].


RAUNKIAER LIFE FORM : 
   Thereophyte


REGENERATION PROCESSES : 
Tumblemustard regenerates entirely from seed.  Seed production is
prolific; large plants can produce an estimated 1.5 million seeds [25].
Seeds are produced in rigid, linear, branchlike siliques approximately 2
to 4 inches (5-10 cm) in length [11].  These seed pods are extremely
tough and do not dehisce readily.  Seeds are uniserate and somewhat
mucilaginous when wet.  Mucilaginous seeds are an adaptation to enhance
germination potential in arid environments by increasing adherence to
soil particles.  This sticky seed coating enables plants to establish on
bare soil.  On overgrazed sagebrush-grassland sites in Nevada
tumblemustard seed reserves were greatest in the litter beneath shrub
canopies, but the majority of plants became established on bare soil in
the shrub interspaces [29].  In fact, on sites with litter buildup
cheatgrass (Bromus tectorum) tends to replace mustard.  Most seeds
germinate in the late fall as soon as rainfall has become sufficient;
some continuous germination occurs the following spring.  Seeds
apparently acquire an environmentally induced dormancy over the cold
winter months which is very similar to that exhibited by cheatgrass
caryopses.  Seeds remain viable in nature for only a short time period
[25].

Tumblemustard is adapted to long-distance seed disperal.  Open-grown
plants assume a dense, rounded form; the entire plant can become
windblown, allowing for "tumbleweedlike" dispersal of seed.  These
highly mobile plants are able to disperse seeds at intervals over
widespread areas and to occupy disturbed areas which are extremely
disjunct in distrubution.  After initial plant establishment, seed
dispersal occurs primarily beneath parent plants; crowding produces
slender, open plants incapable of windblown mobility.  Dense stands are
rapidly established where disturbance is extensive.  Plants are able to
maintain dominance of a site for only a few years as continued crowding
rapidly eliminates plant survival and seed production [20].


SITE CHARACTERISTICS : 
Tumblemustard is an exotic weed species that inhabits disturbed areas
throughout the United States.  Anthropogenic sites such as railroad
rights-of-way, road shoulders, and abandoned farmland have historically
served as seed sources for the rapid invasion of gaps in the native
vegetation.

Within the Intermountain region, tumblemustard occurs on disturbed sites
in both sagebrush-grassland and pinyon-juniper communities [15,18,20,21]
and is favored on sites where a preponderance of bare soil results
following grazing, fire, or cultivation [6].  Tumblemustard does not
appear to be exacting in its site requirements.  It apparently is able
to occupy a variety of soil types and moisture regimes and is somewhat
tolerant of saline soils [7].  Plants will persist on continually
disturbed sites.  Common associates include Russian thistle (Salsola
kali) and cheatgrass.

Elevational ranges for several western states are presented below [7]:

      from 3,700 to 8,500 feet (1,128-2,591 m) in CO
           4,300 to 7,400 feet (1,311-2,256 m) in MT
           4,200 to 7,000 feet (1,280-2,134 m) in UT
           4,100 to 7,400 feet (1,250-2,256 m) in WY


SUCCESSIONAL STATUS : 
Tumblemustard invades disturbed sites within both sagebrush-grassland
and pinyon-juniper communities [15,18,29,30].  Piemeisel [20,21]
completed a classic study of succession on abandoned farmland in
southern Idaho.  His research indicates that tumblemustard frequency is
typically low the first year following disturbance.  During the second
and third years of secondary succession, plants are able to rapidly
increase and dominate sites.  In the absence of disturbance, cheatgrass
will establish itself and virtually eliminate tumblemustard within
approximately 2 years.


SEASONAL DEVELOPMENT : 
Although a winter annual over much of its range, Antos and others [1]
described tumblemustard as a summer annual within a foothills grassland
in northwestern Montana.  Plants can also function as biennials in some
situations [9].  Mechanisms responsible for life cycle diversity in this
species have not been addressed in the literature.

Seeds typically germinate in the fall as soon as rainfall is sufficient.
If germination is early and there is an extended initial growth period
before the onset of winter dormancy, plants form a dense rosette 2 to 4
inches (5-10 cm) in diameter.  Late germination results in overwintering
rosettes with diameters of only 0.4 inch (1 cm) [20].

Plants on abandoned farmland in south-central Idaho exhibited the
following generalized phenological pattern [21]:

          Growth initiation      September through November
          Winter dormancy        December through mid March
          Resumption of growth   April through May
          Maturity               June

Tumblemustard produces abundant flowers on numerous racemes; blooming
generally occurs from May through September [24].  Individual plants
typically flower over an extended period.  Flowers mature rapidly,
resulting in only a few blooming simultaneously.  Apparently flower and
seed phenology are unaffected by the desiccation of the lower basal
leaves [25].

Earliest and latest flowering dates for tumblemustard in several western
states are presented below [7]:

	State           Earliest Flowering       Latest flowering
         CO                    May                   September
         MT                    June                  August
         ND                    May                   August
         UT                    April                 July
         WY                    May                   August

Related categories for Species: Sisymbrium altissimum | Tumblemustard