Cyclachaena

(also Iva), a genus of herbs or shrubs of the family Compositae. The unisexual flowers are in small heads that form a panicled or other type of aggregate inflorescence. There are about 15 species, distributed in the Americas. (Four North American species are often classified in the separate genus Iva.) C. xanthifolia (or Iva xanthifolia), an annual reaching 2 m tall, has large-petioled ovate leaves and a large panicled aggregate inflorescence. The species was imported to Russia in the second half of the 19th century. It is found as a weed in the southern half of the European USSR and, less commonly, in other regions of the country. As a contaminant in hay, it is harmful to livestock; its pollen causes hay fever. The plant is relatively easy to uproot, but some other North American species are difficult to destroy.