Acmella uliginosa

Native to tropical America and introduced widely across the tropics, this annual herb develops erect, sprawling or trailing stems and may reach about 3 feet tall. Small yellow to orange-yellow flowerheads rise singly on slender stalks, with a few short pale yellow rays around the central disk. It grows in damp ground, swampy places and grassland near rivers, and can become a weed in rice fields. In Colombia, it is recorded in the Andes and the Cauca and Magdalena valleys from about 160 to 5,600 feet. Photographed in Colombia.