Longleaf primrose willow is a South American annual that found its way into wetlands across the southeastern United States with consequences still unfolding. Its narrow, willowy leaves are attractive enough, and the yellow flowers that appear from summer through winter catch the eye along drainage channels and slow-moving water. But the plant's talent for seed production is staggering: a mature specimen can generate up to 2.45 million seeds, dispersed by water, wind, and birds in every direction. It tolerates up to twelve inches of standing water and establishes readily in the sandy and silty substrates of marshes, swamps, and riparian corridors.

Dense colonies displace native vegetation, degrade fish habitat, and raise flood risk by restricting waterway flow. Spreading primarily by seed, eradication once established is a long-term project. If grown in a container for observational purposes, a five-gallon pot is the recommended containment, and it should never be sited near any natural waterway. In most contexts, knowing this plant on sight is more valuable than growing it.