Cocklebur

The Cockleburs (Xanthium) are a genus of flowering plants in the family Asteraceae, native to the Americas and eastern Asia.

They are coarse, herbaceous annual plants growing to 50-120 cm tall. The leaves are spirally arranged, with a deeply toothed margin. Some species, notably X. spinosum, are also very thorny with long, slender spines at the leaf bases.

The flowers are of two types; One, in short terminal branches, produces only pollen. The other, in clusters in the axils of the leaves, produces seed.

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 8-20 mm long. It is covered with stiff, hooked spines, which sticks to fur and clothing and can be quite difficult to extract. These remarkable burred seeds have allowed this plant to be carried all over the world by unsuspecting travelers. This plant reproduces only by means of its seed.

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.
 * Selected species
 * Xanthium ambrosioides
 * Xanthium commune
 * Xanthium echinatum - Stinking Cocklebur
 * Xanthium inaequilaterum
 * Xanthium inflexum
 * Xanthium mongolicum
 * Xanthium occidentale - Noogoora Burr
 * Xanthium sibiricum
 * Xanthium speciosum
 * Xanthium spinosum - Spiny Cocklebur, Burreed, Bathurst Burr. South and Central America.
 * Xanthium strumarium - Clotbur, Rough Cocklebur, Large Cocklebur, Common Cocklebur. North America, extensively naturalized elsewhere. Syn. X. canadense, X. chinense,, X. glabratum

Dangers and uses
The Common Cocklebur (X. strumarium) is a native of North America where in the past the (now extinct) Carolina Parakeet 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 medicinal properties and for making yellow dye. The many species of this plant, which can be found in many areas, may actually be varieties of two or three species. Asian species are also used in Chinese traditional medicine.

This plant is a beneficial weed, repelling army worms and other pests from nearby domesticated plants.

There are two other minor uses for cockleburs. Because they readily attach to clothing, they can be used as "darts" in a cocklebur dart game. The burs can also be stuck together to make models.