Ludwigia grandiflora, large-flower primrose-willow, is an emergent perennial aquatic plant native to South America and parts of North America. It is officially classified as a noxious weed or invasive plant in North Carolina, South Carolina and Washington. This species is sometimes broken down into two subspecies, Ludwigia grandiflora ssp. grandiflora and Ludwigia grandiflora ssp. hexapetala.
Foliage
The leaves L. grandiflora attach alternately to the pubescent stems. In early growth stages the leaves usually have a rounded shape growing rosette-like around the villous stem. Once L. grandiflora begins to flower, the leaves lengthen, becoming much more lanceolate to elliptic in shape. Leaves are pilose.
Flowers
L. grandiflora has large yellow flowers that arise from the leaf axils. Each flower has 5-6 petals. Flowers are about 1-2 inches (2-5 cm) in diameter. The floral tube is noticeably shorter than the pedicel.
Fruit
The fruit of L. grandiflora is a cylindrical capsule that is divided into 5 chambers. Fruits have a woody endocarp (inner layer). The seeds are embedded in the endocarp. Estimates put seed production at 10,000 seeds for every square meter of L. grandiflora. L. grandiflora also reproduces from plant fragments. The fragments float and are easily spread by the current or wind blowing along the surface of the water.
Ecological Threat
Ludwigia grandiflora has been introduced to new areas in North America. It has also been introduced to Great Britain, Europe, Australia, Asia and Africa. It grows quickly, covers large areas and forms very dense mats. L. grandiflora is able to grow in riparian as well as aquatic habitats. This plant can significantly alter habitats it invades by outcompeting native species, reducing water oxygen levels and blocking light.