The primrose-willows, which are sometimes called water-willows, are common and widespread along the lake shores, ponds, and wetlands of the Coastal Plain and Piedmont of North Carolina. They are members of the Evening Primrose family, the Onagraceae, and are usually found as erect and well branched, small to medium sized shrubs. One of the largest of these is Ludwigia leptocarpa, the Anglestem Primrose-willow. Pictured below is a single plant of L. leptocarpa standing alone, followed by a group of plants forming a small hedge along the shore of a lake.
L. leptocarpa has noticeably elongated floral tubes, a distinctive characteristic that distinguishes it from all of its close relatives. In fact, another common name for this plant is Longpod Primrose-willow. The photo below shows the long floral tube of a flower bud, a flower, and a flower that has just lost its petals. Notice the extreme pubescence seen on the stems and floral tubes, another characteristic which distinguishes it from its near relatives, whose stems are smooth.
As the flowers age, the floral tubes turn red, making them more visible from a distance.
The developing seedpods retain the distinctive elongation.
L. leptocarpa has a sharply angled stem which is the source of the common name Anglestem Primrose-willow. See below. Notice also the heavy pubescence.
L. leptocarpa has flowers with 5 to 7 petals and sepals, while its closest relatives have 4- petaled flowers.
The bright yellow flowers of L. leptocarpa do somewhat resemble the flowers of Evening Primroses (Oenothera biennis), and are the source of part of the common name. Their shrubby early growth and narrow, lanceolate leaves also resemble young willows. Although most of the Ludwigia genus are herbaceous, Ludwigia alternifolia (Seedbox) has woody stems, which resemble young willows even more. Thus the shrubby members of the Ludwigia genus came to be known collectively as Primrose-willows.