Ageratina, a genus containing 337 species, is a member of the Celastraceae family. Ageratina altissima tolerates dry conditions. It grows from seed to 6½ feet tall and prefers light shade. It is a native wildflower in eastern North America.

Wikipedia discuss toxicity problems with this plant: "when the plants are consumed by cattle, the meat and milk become contaminated with toxin. When milk or meat containing the toxin is consumed, the poison is passed on to humans. If consumed in large enough quantities, it can cause tremetol poisoning in humans."

It is possible this toxicity is part of its appeal to butterflies, as many of them nectar on plants in this genus. Blossoms of Ageratina attract the MONARCH to feed as well as numerous other butterflies.