Ludwigia repens (6 stems)

Ludwigia repens is a species of flowering plant in the evening primrose family known by the common name creeping primrose-willow. It is native to parts of the Americas and it has the potential to spread easily and become naturalized in many areas. It is known as an aquatic weed in some regions. It is also cultivated as an aquarium plant. This is a mat-forming perennial herb with a creeping stem up to 30 centimeters long, rooting at nodes which come in contact with wet substrate. The leaves are oppositely arranged and up to 4 or 5 centimeters long.

The flower has four yellow-colored petals no more than 3 millimeters long nested on a base of four-pointed sepals which may be slightly longer. It makes a fine color contrast to the green shades in the aquarium. Plant in large groups to enhance the decorative effect and prune regularly to encourage bushy growth. The plant makes few demands, but if the light is insufficient the lower leaves tend to fall off. In strong light, the color becomes more intense.