BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Xanthium strumarium | Common Cocklebur 



GENERAL BOTANICAL CHARACTERISTICS : 
Common cocklebur is a native, broadleaved, taprooted, annual forb
[11,33].  Stems are erect, ridged, rough and hairy, and frequently
branched, resulting in somewhat bushy plants from 8 to 59 inches (20-150
cm) tall.  It has small, green unisexual flowers occurring in separate
clusters at the end of the branches and main stem.  The fruit is a
brown, hard, woody bur from 0.4 to 0.8 inch long and covered with stout,
hooked prickles.  Each fruit contains two seeds [32].


RAUNKIAER LIFE FORM : 
   Therophyte


REGENERATION PROCESSES : 
Common cocklebur reproduces by seed only.

Pollination and fruit production:  Pollen transfer is by wind.  The
plant is self-compatible and predominantly self-pollinated.  Common
cocklebur may also set seed without fertilization of the ovule.  Because
of self-compatibility and apomixis, local populations are often
genetically very similar.  A single, open-grown plant typically produces
400 to 500 fruits [14,32].

Fruit dispersal:  The fruits cling to the hide of animals and the
clothing of humans and are dispersed in that manner.  Fruits not
transported by animals fall from the plant during the fall or winter
[18,32].  In riparian habitats, fruits on the soil surface may later be
dispersed by water as they float for up to 30 days [32].  The fruit does
not dehisce, and thus seeds germinate within the fruit.

Seed viability, dormancy, and germination:  Seed viability is usually
high, at least 80 percent [32].  Each bur contains two seeds, one larger
than the other.  The large seed is nondormant and typically germinates
the first spring following production, while the smaller seed germinates
later in the season or, more frequently, the following year [32].
Occasionally, the two seeds germinate simultaneously.

Depth of burial also influences germination.  Seeds lying on the soil
surface and those buried more than 6 inches (15 cm) below the soil
surface rarely germinate.  In Illinois, seed buried in November at
various depths in silty loam soil began to emerge after April 1 and
continued emerging until May 19.  Maximum seedling emergence was from
seed buried at 1 or 2 inches (2.5 and 5.1 cm) [27].  Another study found
that 11 to 16 percent of common cocklebur seeds germinated after 30
months of burial at depths ranging from 3 to 9 inches (8-38 cm) [6].


SITE CHARACTERISTICS : 
Common cocklebur occurs primarily in disturbed, open habitats.  It grows
in cultivated fields, vacant lots, sandpits, and dry washes; on beaches
and sand dunes; and along the shores of ponds and rivers, especially
riverbeds left barren by receding floodwaters [14,18,28,32].  In
noncultivated settings, it primarily occupies beaches and dunes in
eastern North America and floodplains in the West.  In ruderal habitats,
such as agricultural fields, common cocklebur often occurs in dense
stands, but in natural habitats, such as along shorelines, it often
occurs as scattered individuals [18,32].

Common cocklebur is tolerant of a variety of soil conditions ranging
from moist clay to dry sand but grows best on compact sandy soil that is
slightly moist below the soil surface and contains a small amount of
organic matter [32].  It is tolerant of flooding at all growth stages
[32].

Herbaceous associates in various habitats are as follows [10,17,20,26]:

       Habitat                             Associated Herbs

dry, scoured washes within       wild mustard (Brassica campestris) 
southern California              white sweetclover (Melilotus albus)
chaparral (Ceanothus spp.-
Artemisia spp.)

moist and alkaline beds of       Canada wildrye (Elymus canadensis)
intermittent water courses in    prairie cordgrass (Spartina pectinata) 
the Missouri River Breaks of     foxtail barley (Hordeum jubatum)
Montana                          Mexican dock (Rumex mexicanus)
                                 yellow sweetclover (M. officinalis) 

cottonwood (Populus fremontii)   prairie cordgrass (Spartina pectinata)
bottomland along the South       cheatgrass (Bromus tectorum)
Platte River in Colorado         hemp dogbane (Apocynum cannabinum)
                                 curly dock (R. crispus)
                                 guara (Guara parviflora)
                                 poison hemlock (Conium maculatum)
                                 common reed (Phragmites australis)

coastal beaches and sandpits     sea-rocket (Cakile edentula)
of Massachusetts                 seaside goldenrod (Solidago sempervirens)


SUCCESSIONAL STATUS : 
Obligate Initial Community Species

Common cocklebur is a weed of ruderal (sandpits, old fields, cultivated
fields, etc.) and naturally disturbed habitats (beaches, dunes, and
floodplains) [1,18,28].  As a pioneer, it persists only as long as the
ground ramains mostly bare and the site remains unshaded.  It rarely
grows in sod, and plants will not flower or fruit in full shade [18,32].


SEASONAL DEVELOPMENT : 
Seed germination:  

  Illinois - April through mid-May, with lesser numbers through June.  
             Small germination flushes occur throughout the summer with
             adequate moisture [32].  

  southern Ontario - late May [32].

Flowering:  Flowering is controlled by photoperiod.  The plant will not
flower at all or only poorly when day length exceeds 14 hours.  Thus in
the northern portion of its range, flowering does not occur until late
summer [18].  Flowering time by state is as follows:

  Carolinas - July to frost [23]
  Colorado - July to October [5]  
  Kansas - July to November [1]
  Montana - August to September [5]
  North Dakota - July to September [5]
  Wyoming - July to September [34]
  Utah - July to September [34]

Seed dispersal:  Seeds ripen in the fall.  Fruits not removed by animals
fall off the plant in the winter or occasionally remain on the plant
until the next spring [18].

Related categories for Species: Xanthium strumarium | Common Cocklebur