Cockleburs are coarse, herbaceous annual plants growing to 20–47 inches (51–120 cm) tall. The leaves are spirally arranged, with deeply toothed margins. Some species, notably X. spinosum, are also very thorny with long, slender spines at the leaf bases.
Unlike many other members of the family Asteraceae, whose seeds are airborne with a plume of silky hairs resembling miniature parachutes, cocklebur seeds are produced in a hard, spiny, globose or oval double-chambered, single-seeded bur 0.32–0.79 inch (0.81–2.01 cm) long. It is covered with stiff, hooked spines, which sticks to fur and clothing and can be quite difficult to extract. These burs are carried long distances from the parent plant during seed dispersal.
Cockleburs are short-day plants, meaning they only initiate flowering when the days are getting shorter in the late summer and fall, typically from July to October in the Northern Hemisphere. They can also flower in the tropics where the daylength is constant.
The number of species is disputed between different authors, with some recognising as few as three species in the genus.
Species names include:
- Xanthium ambrosioides Hook. & Arn.
- Xanthium argenteum Widder
- Xanthium cavanillesii Shouw
- Xanthium cloessplateaum D.Z.Ma
- Xanthium echinatum Murray - stinking cocklebur
- Xanthium inaequilaterum DC.
- Xanthium italicum Moretti
- Xanthium mongolicum Kitag.
- Xanthium orientale L.
- Xanthium sibiricum Patrin ex Widder
- Xanthium spinosum L. - spiny cocklebur, burreed, Bathurst burr (South and Central America)
- Xanthium strumarium L. - clotbur, rough cocklebur, large cocklebur, common cocklebur (North America, extensively naturalized elsewhere)
Toxicity and uses
The common cocklebur (Xanthium strumarium) is a native of North America where in the now extinct Carolina Parakeet once fed on the seeds. It has become an invasive species worldwide. It invades agricultural lands and can be poisonous to livestock, including horses, cattle, and sheep. Some domestic animals will avoid consuming the plant if other forage is present, but less discriminating animals, such as pigs, will consume the plants and then sicken and die. The seedlings and seeds are the most toxic parts of the plants. Symptoms usually occur within a few hours, producing unsteadiness and weakness, depression, nausea and vomiting, twisting of the neck muscles, rapid and weak pulse, difficulty breathing, and eventually death.
The plant also has been used for making yellow dye, hence the name of the genus (Greek xanthos = 'yellow'). The many species of this plant, which can be found in many areas, may actually be varieties of two or three species. The seed oil is edible to humans.
X. strumarium is known as cang er zi (苍耳子) in traditional Chinese medicine. According to some studies, an active ingredient in Xanthium selectively modulates superoxide anion generation by human neutrophils induced by N-formyl-methionine-leucine-phenylalanine (namely fMLP, acts as a strong chemoattractant), with an IC50 value of 1.72 µg/mL. Xanthium is also used to treat nasal and sinus congestion.
The spines and seeds of this fruit are rich in a chemical called carboxyatractyloside (CAT), formerly referred to as xanthostrumarin, which is the chemical that is responsible for most of the adverse effects from the use of cang er zi. CAT has been shown to be a growth inhibitor in Xanthium and other plants, serving two functions, delaying seed germination and inhibiting the growth of other plants. Most of the chemical is concentrated in the spines. When the bur is prepared as an herbal remedy, the spines are usually removed, reducing the CAT content of the finished product.
- Xanthium in The Plant List
- Lee, C. L., et al. (2008). "(-)-Xanthienopyran, a new inhibitor of superoxide anion generation by activated neutrophils, and further constituents of the seeds of Xanthium strumarium". Planta medica 74 (10): 1276–9. doi:10.1055/s-2008-1081295. PMID 18622908.
- English, J. (2010). "Natural Allergy Relief". Nutrition Review 4 (2). Retrieved 2012-01-03.
- Cutler, H. G. and R. J. Cole. (1983). Carboxyatractyloside: A compound from Xanthium strumarium and Atractylis gummifera with plant growth inhibiting properties. Journal of Natural Products 46(5) 609-13.
- Everitt, J. H., et al. (2007). Weeds in South Texas and Northern Mexico. Lubbock: Texas Tech University Press. ISBN 0-89672-614-2