Ludwigia hexapetala

Native to parts of North, Central, and South America, this perennial waterprimrose grows as an aquatic plant or sprawling subshrub. Creeping stems float across shallow water and root at their nodes, producing upright flowering shoots. Solitary, bright yellow flowers open above the water. The plant can expand into tangled mats along slow-moving rivers, pond margins, canals, and other wet habitats. It has become invasive in France, where dense growth can overtake wetland vegetation. Photographed in Colombia.