The ragweeds, the genus Ambrosia, in the sunflower family, Asteraceae, are all endemic to the Americas. Of the 22 species native to North America, only five are widespread (see USDA maps). But two species are in every one of the lower 48 states, annual ragweed Artemisia artemisifolia, and western ragweed, Artemisia psilostachya. They look very similar. The annual ragweed has always been a plant of disturbed areas, spending the winter as seeds, needing relatively open conditions to prosper during its one year of life. Human disturbances have given it many more places to grow. The other widespread ragweed, western ragweed, is a perennial, and is found in native ecosystems all across the United States.