Ludwigia peruviana

Native from southern Mexico through tropical America, this upright perennial wetland shrub can reach about 10 feet tall. It grows along creek banks, in marshes and in still or slow-moving water. Its yellow flowers usually have four petals and last for one day. The reddish-brown seed capsules retain their sepals and are square in cross-section. In New South Wales, Australia, introduced plants form dense colonies that obstruct waterways and displace native aquatic vegetation. Seeds travel in flowing water and on birds, while broken root or stem pieces can establish new colonies downstream. Photographed in the Sierra Nevada de Santa Marta, Colombia.