Poisonous Plants of the Southern United States - Page 15 Poisonous Plants of the Southern United States common cocklebur Xanthium pensylvanicum Coarse, widely branching, annual herb .2 to 1.7 in tall. Leaves alternate, simple, coarsely pubescent, shallowly 3 to 5 lobed.
Flowers green inconspicuous, male and female borne in separate clusters.
Fruit broadly cylindrical, to nearly spherical, spiny, 1.5 to 3 cm long including spines, two-seeded, greenish to brown at maturity. The toxic principle is the glycoside, hydroquinone. Mature plants are distasteful to animals and contain less of the toxin. They root up and ingest the two-leaf stage of the plant in the springtime. Symptoms include vomiting and gastrointestinal irritation with occasional diarrhea.