Cocklebur (Xanthium strumarium
) is a coarse, erect, annual plant belonging to the Asteraceae (Sunflower) family. Cocklebur is native to and found throughout North America and Eurasia. Cocklebur plants are most likely to be found in disturbed, poorly drained areas. Cocklebur attributes:
- Height: Grows to about 3 feet tall
- Young plants Cocklebur seedlings appear as a whitish-green stem with two strap-shaped green leaves.
- Leaves: Cocklebur has alternate, rough, broadly triangular to heart-shaped leaves.
- Stems: Cocklebur stems are round to slightly rubbed, covered with short white hairs along the surface, and are often speckled with purple.
- Fruits: Cocklebur fruits are small, hard, oval-shaped, 2-chambered burs that are covered with strong, hooked spines.
- Flowers: Cocklebur plants produce two different types of flowers depending on whether the plant is male or female. Male plants produce short, terminal branches of flowers along the upper half of the plant. Each male compound flower occurs on a short pedicel and is slightly rounded at the top. Female plants develop clusters of flowers within the axils of the leaves, in the lower half of the plant. Each female compound flower contains 2 pistillate florets, which are nearly enclosed by a prickly floral bract with a bur-like appearance. The female compound flowers are initially green, but turn brown as they mature and are slow to detach from the racemes. Both flower types bloom during the later summer or early fall.
- Root System: Cocklebur has a stout, rather woody taproot.
All parts of cocklebur are toxic to livestock, however horses are at greatest risk of poisoning when the plant is first emerging, during the early seedling stage. During this stage of growth, cocklebur contains higher levels of toxins, and is also more attractive to animals. Ingestion of 0.75% of the horse's body weight can result in signs of poisoning, occurring within a few hours. Death usually follows 24 to 48 hours later.
The primary toxin in cocklebur is carboxyatractyloside, a sulfated glycoside. Younger horses are more at risk of toxicity and most cases of poisoning in animals occur in the spring and summer. Horses are also at risk of impaction colic from consuming mature fruits during late summer/early fall.
Horses may develop acute or chronic toxicity as a result of consumption of cocklebur. In acute cases, death is usually due to liver failure and may occur within hours after onset of clinical signs. Horses that survive acute poisonings usually will develop signs of chronic liver disease.