Xanthium
| cocklebur | |
|---|---|
 |
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| Xanthium strumarium | |
| Scientific classification | |
| Kingdom: | Plantae |
| (unranked): | Angiosperms |
| (unranked): | Eudicots |
| (unranked): | Asterids |
| Order: | Asterales |
| Family: | Asteraceae |
| Tribe: | Heliantheae |
| Genus: |
Xanthium L. |
| Type species | |
|
Xanthium strumarium L. |
|
| Synonyms | |
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Xanthium (cocklebur) is a genus of flowering plants in the sunflower tribe within the daisy family, native to the Americas and eastern Asia.
Cockleburs are coarse, herbaceous annual plants growing to 20–47 inches (51–119 cm) tall. The leaves are spirally arranged, with deeply toothed margins. Some species, notably Xanthium spinosum, are also very thorny with long, slender spines at the leaf bases.
The flower heads 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 0.32–0.79 inches (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 by help of animals (zoochorous).
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.
Over 200 names have been proposed for species, subspecies, and varieties within the genus. Most of these are regarded as synonyms of highly variable species. Some recognize as few as two or three species in the genus. The Global Compositae Checklist recognizes the following
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