Acmella repens (Creeping spotflower)

Native from the central and southeastern United States through Mexico and Central America to Venezuela and Paraguay, and also to Cuba, this plant is a spreading perennial herb. It grows in wet ground beside swamps, ditches and low woodland. Its stems root where the lower nodes touch the ground, producing spreading patches. The mostly opposite leaves have pointed tips and toothed edges. Each flower head has short yellow petals surrounding a raised center packed with tiny tubular flowers. The outer flowers are female, while those in the center have both male and female parts. Photographed in Colombia.