Ambrosia artemisiifolia, with the common names common ragweed, annual ragweed, and low ragweed, is a species of the genus Ambrosia native to regions of the Americas. Taxonomy The species name, artemisiifolia, is given because the leaves were thought to bear a resemblance to the leaves of Artemisia, the true wormwoods. It has also been called the common names: American wormwood, bitterweed, blackweed, carrot weed, hay fever weed, Roman wormwood, short ragweed, stammerwort, stickweed, tassel weed. Distribution The plant is native to: North America across Canada, the eastern and central United States, the Great Plains, and in Alaska; the Caribbean on Cuba, Hispaniola, and Jamaica; and South America in the southern bioregion (Argentina, Chile, Paraguay, Uruguay), the western bioregion (Bolivia, Peru), and Brazil. The distribution of common ragweed in Europe is expected to expand northwards in the future due to climate change. It is the most widespread species of the genus in North America, to which most of the other species of Ambrosia are endemic. During the summer it causes allergic reaction in those that are susceptible. Description Ambrosia artemisiifolia is an annual plant that emerges in late spring. It propagates mainly by rhizomes, but also by seed. It is much-branched, and grows up to in height. The pinnately divided soft and hairy leaves are long. Its bloom period is July to October in North America. Its pollen is wind-dispersed, and can be a strong allergen to people with hay fever. It produces 2–4 mm obconic green to brown fruit. It sets seed in later summer or autumn. Since the seeds persist into winter and are numerous and rich in oil, they are relished by songbirds and upland game birds. Invasive species Common ragweed, Ambrosia artemisiifolia, is a widespread invasive species, and can become a noxious weed, that has naturalized in: Europe; temperate Asia and the Indian subcontinent; temperate northern and southern Africa and Macaronesia; Oceania in Australia, New Zealand, and Hawaii; and Southwestern North America in California and the Southwestern United States. A scientific study investigated the genomic basis of invasiveness in Ambrosia artemisiifolia, introduced to Europe in the late 19th century, by resequencing 655 ragweed genomes, including 308 herbarium specimens collected up to 190 years ago. In invasive European populations, the study found selection signatures in defense genes and lower prevalence of disease-inducing plant pathogens. Together with temporal changes in population structure associated with introgression from closely related Ambrosia