Creeping Water Primrose
Ludwigia peploides glabrescens
Evening Primrose family (Onagraceae)

Description: This perennial plant is –2' long. It either floats on water or sprawls across the ground. The stems are light green to red (often the latter), glabrous to sparsely pubescent, and terete. Alternate leaves along these stems are 1–3" long and –1" across; they are elliptic, oblong-elliptic, oblanceolate, or oblong-oblanceolate in shape and smooth along their margins. The leaves are usually glossy green in appearance, although sometimes they develop patches of red or yellow. The upper leaf surface is glabrous, while the lower leaf surface is glabrous to sparsely pubescent. The leaf bases taper gradually into slender petioles about –2" long. Individual flowers develop from the axils of the middle to upper leaves on erect to semi-erect pedicels about 1–3" long. Each flower is about 1" across, consisting of 5 yellow petals, 5 light green sepals, 10 yellow stamens, and a narrowly cylindrical pistil with a single style. The petals are obovate in shape with pale pinnate nerves, while the smaller sepals are lanceolate. Compared to the size of the flower, both the stamens and style are relatively short. Between the apex of the pedicel and the bottom of the pistil, there is a pair of tiny bractlets (about 1.0–1.5 mm. in length). The blooming period occurs from late spring to early fall, lasting several months. The flowers are diurnal.

Afterwards, the flowers are replaced by cylindrical seed capsules about 1–1" long. Each seed capsule has 5 narrow cells, and each cell contains a row of seeds. The seeds are enclosed in chunky outer coatings (endocarps); they are about 1.0-1.5 mm. in length. The root system is fibrous and fleshy. When the nodes of the stems lie on wet ground, they are capable of developing new fibrous roots, from which new plants are produced vegetatively. Sometimes the root system produces small bladders that keep individual plants more buoyant in the water. This plant often forms large colonies.

Cultivation: The preference is full sun, wet conditions, and muddy soil, although this plant can adapt to shallow water as a floating aquatic. Creeping Water Primrose (Ludwigia peploides glabrescens) can spread aggressively in shallow wetlands and muddy areas. It is potentially invasive.

Range & Habitat: Creeping Water Primrose is locally common and native to southern Illinois, while in the rest of the state it is uncommon and probably adventive in most areas (see Distribution Map). This species is slowly spreading northward. Habitats include borders of ponds, shallow areas of lakes, sluggish streams, swamps, marshes, and ditches. In some of these habitats, Creeping Water Primrose can become the dominant shoreline plant, forming large colonies.

Faunal Associations: The flowers are cross-pollinated primarily by bees, including honeybees, digger bees (Eucerine), and Halictid bees. Other visitors, such as flies and skippers, are less effective at cross-pollination. These insects obtain nectar and/or pollen from the flowers. Some insects feed destructively on Creeping Water Primrose. This includes the flea beetles, Altica litigata and Lysathia ludoviciana, and a leafhopper, Draeculacephala inscripta. The Mallard and possibly other ducks feed on the seed capsules. Because of the large dense colonies that this plant often forms, it provides good cover along shorelines for various insects, frogs, and other wetland wildlife.

Photographic Location: Muddy shore of a pond in southern Illinois.

Comments: Creeping Water Primrose has showy flowers and attractive foliage. Unfortunately, it is sometimes too aggressive for its own good. It can be distinguished from other Ludwigia spp. by its larger 5-petaled flowers and sprawling semi-aquatic habit. Across its range in the United States and tropical America, different varieties of this species have been described, although only var. glabrescens has been found in Illinois. This variety can be distinguished by its more glabrous foliage. Another scientific name of this wetland plant is Jussiaea repens glabrescens, while an alternative common name is Creeping Primrose Willow.