Common cocklebur

Xanthium strumarium L.

Images above: Upper left: Common cocklebur seedling (Antonio DiTommaso, Cornell University). Upper right: Common cocklebur streaked stem and immature burs (Scott Morris, Cornell University). Bottom: Common cocklebur mature plant (Scott Morris, Cornell University).


Other common names:  clotbur, cocklebur, broad-leaved cocklebur, clotbur, sheep-bur, ditch-bur, button-bur, noogoora bur, heartleaf cocklebur, rough cocklebur

Family:  aster family, Asteraceae

Habit:  Erect summer annual herb.

Description:  Seedlings have short, thick stems with purple at the base.  Seed leaves are lance shaped, 2” by 0.5” (5.1 by1.3 cm) and narrower at each end, hairless, thick, dark green above and light green below.  The first pair of true leaves is opposite, triangular to egg shaped with a rounded tip, and slightly toothed, with three prominent surface veins.  All other young leaves are alternately attached, distinctly toothed, egg shaped with a pointed tip, and covered in rough, short hairs.  The stem becomes green and covered with upward pointing hairs as the plant develops.  Fully mature stems are green, 1-4 ft (30.5-122 cm) tall, highly branched, hairy, and flecked with purple-brown to black spots.  Ridges are present on the stem.  Upright hairs cause leaves to feel abrasive and gritty.  Leaves are alternate, 1-6” (2.54-15.2 cm) long, and oval to triangular or heart-shaped.  Edges are wavy, irregularly toothed, and slightly lobed into 3 to 5 sections: the two lobes near the leaf junction with the stalk give the leaf a heart shaped base and the ones near the leaf tip may be slightly pointed.  The leaf stalk is 0.75-3” (1.9-7.6 cm) long.  The semi-woody, broad, and sturdy taproot can reach 4 ft (122 cm) deep.  Heads of either all male or all female green flowers appear in leaf axils near branch tips, but both sexes occur on the same plant.  Individual flowers are inconspicuous.  Male heads are 0.2-0.3” (0.51-0.76 cm) across and are subtended by 1 to 3 rows of small green bracts.  Individual male flowers are round and short-lived, dropping off after shedding pollen.  Female flowers are contained within small, green, immature burs.  Fruit is a woody, brown, egg-shaped to elliptical bur.  Each bur is approximately 1” (2.54 cm) long by 0.7” (1.78 cm) or less wide, is covered in hard 0.1-0.25” (0.25-0.64 cm) spines, and has two beaklike projections at the tip.  Each bur contains two oblong, pointed, light brown to black seeds, covered in a papery, silver-black membrane.  Each bur contains one large and one small seed, 0.31-0.60” (0.79-1.52 cm) long by 0.2-0.3” (0.51-0.76 cm) wide.

Similar species:  Four species are sometimes mistaken for common cocklebur: jimsonweed (Datura stramonium L.), spiny cocklebur (Xanthium spinosum L.), common burdock (Arctium minus Bernh.) and great burdock (Arctium lappa L.).  Jimsonweed can be confused for cocklebur at the seedling stage, but can be distinguished by its hairless stems, singly veined leaves, and unpleasant odor.  Spiny cocklebur has yellow spines at the leaf nodes, more slender leaves, and beakless burs.  Common burdock and great burdock also produce burs, but have larger 20” by 16” (50.8 by 40.6 cm) leaves, and burs that break into individual, spined fruits.


Common cocklebur is an extremely competitive weed due to fast emergence and rapid growth supported by the large seed. Populations of 1-3 plants per 10 square ft can cause soybean yield losses of 52-75% (Weaver and Lechowicz 1982). Common cocklebur emerges faster and in higher numbers (Norsworthy and Oliveira 2007c) and is more competitive (Bararpour and Oliver 1998) under tillage than no-tillage conditions, so no-tillage grain production will be less favorable to this weed. Because the seedlings can emerge from deep in the soil, tine weeding and rotary hoeing have limited effectiveness. Cultivate row crops early, close to the row, and repeat regularly until the crop is too large to tolerate tractor traffic. If plants set seed before harvest, collect or destroy the seeds during combining. Electrocution with a Weed ZapperTM controlled most plants that were reproductive and growing above a crop canopy, while it reduced viability of the majority of seeds present during treatment (Schreier et al. 2022).

Because the seeds do not persist well in the soil, rotation to a sod crop for several years will help control this weed.  Rotation to a winter grain will also help because the burs do not mature by grain harvest.  Disk the field and plant a cover crop after grain harvest to prevent re-sprouting from the shoot bases and subsequent seed production.

 Soil solarization so that mid-day soil temperatures reach 149-156 °F (65-69 °C) will eliminate a high proportion of common cocklebur seeds (Egley 1983).

Common cocklebur often establishes first on unmanaged areas, so eradicate it quickly from these areas before it can invade your tilled fields.


Origin and distribution:  Common cocklebur is probably native to North, Central and South America, and possibly also to southern Europe and South Asia. It also occurs in Africa and has been introduced into Australia.  The natural habitat of this species is along river banks and beaches, and it has colonized agricultural fields, roadsides and other disturbed habitats in more recent times.  (Blais and Lechowicz 1989, Weaver and Lechowicz 1982)

Seed weight: small (upper) seed, 50 mg; large (lower seed), 60 mg (Weaver and Lechowicz 1982).  Burs can vary considerably in size (Wasson et al. 2002).  A large proportion of small and intermediate sized burs have either no seeds or only one seed; for large burs containing two seeds, seed weight was 50 mg for the small seed and 75 mg for the large seed (Zimmerman and Weis 1983). 

Dormancy and germination:  Burs usually contain two seeds, and these differ in size and dormancy (Weaver and Lechowicz 1982, Zimmerman and Weis 1983).  The smaller (upper) seed often sits closer to the tip of the bur and is usually dormant.  The larger (lower) seed usually germinates the next spring following an afteripening period.  The smaller seed usually does not germinate until summer or the following year; this dormancy is apparently due to germination inhibitors in the seed coat and inability of oxygen to pass through the seed coat.  Germination of both types of seeds is promoted by microbial decay or mechanical seed coat damage.  The seeds do not require light for germination (Norsworthy and Oliveira 2007a, Stoller and Wax 1974).   A daily temperature alternation of 27 °F (15 °C) increased germination over that at constant temperatures (Norsworthy and Oliveira 2007a).  Germination was greatest with warm, fluctuating temperatures of 86/68 °F (30/20 °C) to 91/77 °F (33/25 °C) (Weaver and Lechowicz 1982, Norsworthy and Oliveira 2007a).  Under a constant temperature regime, highest germination occurred at 95-104 °F (35-40 °C), but constant soil temperatures of this magnitude are unlikely to occur under natural field conditions (Norsworthy and Oliveira 2007a).

Seed longevity:  Based on measurements at 6 to 30 months, common cocklebur seed viability declines at about 50% per year (Egley and Chandler 1978).  In Arkansas, no common cocklebur seeds were viable three years after being shed (Bararpour and Oliver 1998).  In Nebraska, some seeds buried in plastic capsules survived for 9 years (Burnside et al. 1996).

Season of emergence:  Most emergence occurs in mid-spring to early summer, with occasional pulses of seedlings appearing later in the summer as well (Bararpour and Oliver 1998, Doll 2002, Norsworthy and Oliveira 2007c, Stoller and Wax 1973, Weaver and Lechowicz 1982, Werle et al. 2014, Zimmerman and Weis 1984).  Emergence is dispersed more evenly from late-spring throughout summer under no-tilled than tilled conditions (Norseworthy and Oliveira 2007c).  The lowest average soil temperature required for emergence was 63 °F (17 °C) and the minimum alternation in day-to-night soil temperature required for emergence was 14 °F (7.5 °C) (Norsworthy and Oliveira 2007b). 

Emergence depth:  Common cocklebur emerges well from 0.4 to 4” (1 to 10 cm) of soil and a few seedlings can emerge from as deep as 6” (15 cm) (Stoller & Wax 1973, Weaver and Lechowicz 1982).   Seeds usually cannot take up enough water to germinate when they are on the soil surface due to poor contact between the large seeds and soil (Bararpour and Oliver 1998).

Photosynthetic pathway:  C3 (Weaver and Lechowicz 1982)

Sensitivity to frost:  Common cocklebur tolerates only light frost (Weaver and Lechowicz 1982).

Drought tolerance:  Common cocklebur is drought tolerant.  Roots can extend 7 ft (2.1 m) laterally and 4 ft (1.2 m) deep, allowing access to water throughout the soil profile (Weaver and Lechowicz 1982).  Common cocklebur is an aggressive competitor partially because of its capacity to take up more water than other crops or weeds under similar growth conditions (Jones and Walker 1993, Patterson and Flint 1983).  It can maintain photosynthesis and transpiration under drought stress better than soybean, but its growth and reproduction is reduced by prolonged drought (Mortensen and Coble 1989).

Mycorrhiza:  Common cocklebur is considered a strong mycorrhizal host (Vatovec et al. 2005).

Response to fertility:  Common cocklebur is highly responsive to N.  In high N conditions, it will store excess N as nitrate and later use it to increase seed production (Weaver and Lechowicz 1982).  It grows well at pH 5.2 to 8.0 (Weaver and Lechowicz 1982).

Soil physical requirements:  The species grows in a wide range of soil types from coarse sand to heavy clay (Holm et al. 1977, Weaver and Lechowicz 1982).  It can tolerate flooded as well as dry soil conditions (Weaver and Lechowicz 1982).

Response to shade:  Shade reduces growth and delays flowering of common cocklebur (Kaul 1971).  In the absence of root competition, shade from a soybean leaf canopy reduced cocklebur water uptake, leaf area and weight (Jones and Walker 1993).  Cocklebur has the capacity to maintain functionality of lower leaves within the shade of a crop canopy by adjusting leaf metabolism accordingly (Regnier et al. 1988).  It also has the potential to alter upper leaf growth to increase light capture in response to reduced light levels on lower leaves (Regnier and Harrison 1993). 

Sensitivity to disturbance:  Very rapid growth and ability to emerge from deep layers in the soil make common cocklebur insensitive to tine weeding and rotary hoeing.  Small plants regrow quickly from buds at the base of lower leaves if plants are trampled or clipped.  Once flowers have been pollinated, the burs will produce mature seeds even if the shoot or branch is severed from the roots.  (Weaver and Lechowicz 1982)

Time from emergence to reproduction:  Plants flower as days shorten and generally flowering begins in August regardless of age or size (Wasson et al. 2002, Weaver and Lechowicz 1982).  Seed maturation continues until a killing frost.  Flowering initiated 16 weeks after emergence in Arkansas (Bararpour and Oliver 1998) and Wisconsin (Doll 2002), but 10 weeks after emergence in Quebec (Blais and Lechowicz 1989).  Seeds become viable early in development.  A few seeds are viable when burs begin to form, but the majority are viable when burs are fully elongated about 3 weeks later (Clay and Griffin 2000).  In India, time from appearance of first flowers to ripening of first fruit was 23 days (Kaul 1971).

Pollination:  Common cocklebur primarily self pollinates, but up to 12% of flowers are cross pollinated by wind dispersed pollen (Weaver and Lechowicz 1982).

Reproduction:  Vigorous, open grown plants produce between 500 and 5,400 burs, each of which usually contains two seeds.  However, in dense stands, plants produced only 71 to 586 burs per plant (Weaver and Lechowicz 1982).  In pure stands in Arkansas, individual plants produced 4,500 burs (= 9,000 seeds) (Bararpour and Oliver 1998), whereas in Quebec, plants produced 1,300 to 3,500 seeds (Blais and Lechowicz 1989).  Individual cocklebur plants produced 900 burs (= 1,800 seeds) when grown with soybeans in North Carolina (Mortensen and Coble 1989).  The number of burs depends entirely on the size of the plant at the time flowering begins (Weaver and Lechowicz 1982).  Seeds shattered at the time of soybean harvest ranged from 6 to 61% across eight site-years (Schwartz-Lazaro et al. 2021).

Dispersal:  The spiny burs cling to animal fur, clothing, grain sacks, etc.  They tangle particularly well in sheep's wool and are dispersed when the animals or wool is transported.  The burs float well and are readily dispersed in streams, lakes, irrigation ditches and flooded fields. (Weaver and Lechowicz 1982)

Common natural enemies:  The moth, Phaneta imbridana, lays eggs on the bur wall, and the larvae bore in and eat the seeds (Hare 1977).  The fly, Euaresta aequalis, pierces the bur wall and lays its eggs directly on the developing seeds (Hare 1977).  Together these insects killed from 3-84% of the seeds in New York.  Population variation in bur characteristics greatly affects seed mortality, with long spines inhibiting the fly and thick bur walls inhibiting the moth (Hare 1980).  Two stem beetles burrow down through the stem and overwinter in the root, but they only affect seed set in the branches that they actually damage (Weaver and Lechowicz 1982).  The rust, Puccinia xanthii, is common in the U.S.A. and affects only cocklebur and ragweed species (Weaver and Lechowicz 1982).  It causes deformed leaves, early leaf drop, cracks on the stem, reduced plant size and reduced seed viability.  Spores overwinter on dead plants which offers some possibility for deliberately spreading the disease using powdered diseased plants.

Palatability:  People do not consume common cocklebur, but the seeds have been used in herbal medicine.  The seed leaves (cotyledons) are highly toxic to livestock (Burrows and Tyrl 2006).  Larger plants have good nutritional value for livestock but are rough and unpalatable (Weaver and Lechowicz 1982).  Crude protein was higher during mid-summer and digestibility was higher during most of the season than that of a mixed tall fescue and legume standard (Bunton et al. 2020).  Common cocklebur was unpalatable to grazing sheep (Marten and Andersen 1975). 

Notes:  The pollen of cocklebur produces hay fever symptoms in sensitive individuals, and contact with the stems can also cause dermatitis in some individuals (Weaver and Lechowicz 1982).


  • Bararpour, M. T., and L. R. Oliver.  1998.  Effect of tillage and interference on common cocklebur (Xanthium strumarium) and sicklepod (Senna obtusifolia) population, seed production, and seedbank.  Weed Science 46:424-431.
  • Blais, P. A., and M. J. Lechowicz.  1989.  Variation among populations of Xanthium strumarium (Compositae) from natural and ruderal habitats.  American Journal of Botany 76:901-908.
  • Bunton, G., Z. Trower, C. Roberts, and K. W. Bradley.  2020.  Seasonal changes in forage nutritive value of common weeds encountered in Missouri pastures. Weed Technology 34:164–171.
  • Burnside, O. C., R. G. Wilson, S. Weisberg, and K. G. Hubbard.  1996.  Seed longevity of 41 weed species buried 17 years in eastern and western Nebraska.  Weed Science 44:74-86.
  • Burrows, G. E., and D. J. Tyrl.  2006.  Handbook of Toxic Plants of North America. Blackwell: Ames, IA.
  • Clay, P. A., and J. L. Griffin.  2000.  Weed seed production and seedling emergence responses to late-season glyphosate applications.  Weed Science 48:481-486.
  • Doll, J.  2002.  Knowing when to look for what: Weed emergence and flowering sequences in Wisconsin.
  • Egley, G. H.  1983.  Weed seed and seedling reductions by soil solarization with transparent polyethylene sheets.  Weed Science 31:404-409.
  • Egley, G. H., and J. M. Chandler.  1978.  Germination and viability of weed seeds after 2.5 years in a 50-year buried seed study.  Weed Science 26:230-239.
  • Hare, J. D.  1977.  The biology of Phaneta imbridana (Lepidoptera:Tortricidae), a seed predator of Xanthium strumarium (Compositae).  Psyche 84:179-182.
  • Hare, J. D.  1980.  Variation in fruit size and susceptibility to seed predation among and within populations of the cocklebur, Xanthium strumarium L.  Oecologia 46:217-222.
  • Jones, R. E. Jr., and R. H. Walker.  1993.  Effect of interspecific interference, light intensity, and soil moisture on soybean (Glycine max), common cocklebur (Xanthium strumarium), and sicklepod (Cassia obtusifolia) water uptake.  Weed Science 41:534-540
  • Kaul, V.  1971.  Physiological-ecology of Xanthium strumarium Linn. IV. Effect of climatic factors on growth and distribution.  New Phytologist 70:799-812.
  • Marten, G. C., and R. N. Andersen.  1975.  Forage nutritive value and palatability of 12 common annual weeds.  Crop Science 15:821-827.
  • Mortensen, D. A., and H. D. Coble.  1989.  The influence of soil water content on common cocklebur (Xanthium strumarium) interference in soybeans (Glycine max).  Weed Science 37:76-83.
  • Norsworthy, J. K., and M. J. Oliveira.  2007a.  Light and temperature requirements for common cocklebur (Xanthium strumarium) germination during after-ripening under field conditions.  Weed Science 55:227-234.
  • Norsworthy, J. K., and M. J. Oliveira.  2007b.  A model for predicting common cocklebur (Xanthium strumarium) emergence in soybean.  Weed Science 55:341-345.
  • Norsworthy, J. K., and M. J. Oliveira.  2007c.  Tillage and soybean canopy effects on common cocklebur (Xanthium strumarium) emergence.  Weed Science 55:474-480.
  • Patterson, D. T., and E. P. Flint.  1983.  Comparative water relations, photosynthesis, and growth of soybean (Glycine max) and seven associated weeds.  Weed Science 31:318-323.
  • Regnier, E. E., and S. K. Harrison.  1993.  Compensatory responses of common cocklebur (Xanthium strumarium) and velvetleaf (Abutilon theophrasti) to partial shading.  Weed Science 41:541-547.
  • Regnier, E. E., M. E. Salvucci, and E. W. Stoller.  1988.  Photosynthesis and growth responses to irradiance in soybean (Glycine max) and three broadleaf weeds.  Weed Science 36:487-496.
  • Schreier, H., M. Bish, and K. W. Bradley. 2022. The impact of electrocution treatments on weed control and weed seed viability in soybean. Weed Technology 36:481–489.
  • Schwartz-Lazaro L. M., L. S. Shergill, J. A. Evans, M. V. Bagavathiannan, S. C. Beam, M. D. Bish, J. A. Bond, K. W. Bradley, W. S. Curran, A. S. Davis, W. J. Everman, M. L. Flessner, S. C. Haring, N. R. Jordan, N. E. Korres, J. L. Lindquist, J. K. Norsworthy, T. L. Sanders, L. E. Steckel, M. J. VanGessel, B. Young, and S. B. Mirsky.  2021.  Seed-shattering phenology at soybean harvest of economically important weeds in multiple regions of the United States. Part 1: Broadleaf species. Weed Science 69:95–103.
  • Stoller, E. W., and L. M. Wax.  1973.  Periodicity of germination and emergence of some annual weeds.  Weed Science 21:574-580.
  • Stoller, E. W., and L. M. Wax.  1974.  Dormancy changes and fate of some annual weed seeds in the soil.  Weed Science 22:151-155.
  • Vatovec, C., N. Jordan, and S. Huerd.  2005.  Responsiveness of certain agronomic weed species to arbuscular mycorrhizal fungi.  Renewable Agriculture and Food Systems 20:181–189.
  • Weaver, S. E., and M. J. Lechowicz.  1982.  The biology of Canadian weeds.  56.  Xanthium strumarium L.  Canadian Journal of Plant Science 63:211-225.
  • Werle, R., L. D. Sandell, D. D. Buhler, R. G. Hartzler, and J. L. Lindquist.  2014.  Predicting emergence of 23 summer annual weed species.  Weed Science 62:267-279.
  • Wasson, J. J., P. J. Patrick, and L. M. Wax.  2002.  Variation among U.S. accessions of common cocklebur (Xanthium strumarium).  Weed Technology 16:171-179.
  • Zimmerman, J. K., and I. M. Weis.  1983.  Fruit size variation and its effects on germination and seedling growth in Xanthium strumarium.  Canadian Journal of Botany 61:2309-2315.
  • Zimmerman, J. K., and I. M. Weis.  1984.  Factors affecting survivorship, growth, and fruit production in a beach population of Xanthium strumarium.  Canadian Journal of Botany 62:2122-2127.