Ambrosia psilostachya, also known as Cuman ragweed, American wormwood, and perennial ragweed, is a species of flowering plant in the sunflower family. Native to North and Central America, this plant can grow up to six feet tall and has greenish-yellow flowers that bloom in late summer and early fall. Although ambrosia psilostachya is an important source of food for some animals, its pollen can cause severe allergic reactions in humans. Some synonyms for ambrosia psilostachya include ghostweed, western ragweed, and prairie ragweed. Other closely related species of ambrosia include ambrosia artemisiifolia (common ragweed) and ambrosia trifida (giant ragweed).