Acmella ciliata

Native from Panama through tropical South America to northern Argentina, this herbaceous perennial grows about 1 to 3 feet tall. Its spreading or ascending stems can root where their joints touch the ground. The yellow flowerheads have a raised center of tiny disc flowers surrounded by five to ten ray flowers. It favors damp, disturbed places and has naturalized in India, Thailand, Sumatra and Sulawesi in Indonesia, Taiwan and Guangxi in southern China. It has a history of traditional use for toothache and other mouth complaints. Photographed in Ecuador.