Floating Mat Rooted Plants
hexapetala (Hook. & Arn.) Zardini, Gu, & Raven (synonym Jussiaea
uruguayensis), water primrose
Ludwigia palustris (L.) Ell., water purslane
These perennial herbs can be found creeping on the shoreline, floating on the water surface, or growing upright. Water primrose is a robust plant with bright yellow showy flowers and willow-like leaves. It is non-native and forms dense mats in sloughs along the lower Columbia River. Water purslane is smaller and has inconspicuous flowers and opposite leaves. Although these two species are closely related, they do not resemble each other in appearance.
Leaf: Water primrose: alternate, to 12 cm long, leaf stalks about 2 cm long, slightly hairy. Water purslane: reddish, opposite, elliptical, to 5 cm long, on stalks nearly as long as the leaf blades.
Stem: Lying flat, floating, or erect. Water primrose: to 2 m long, robust, often hairy. Water purslane: to 50 cm long, slender, not hairy, rather succulent.
Flower: Blooms throughout summer. Water primrose: yellow, showy, normally with 5 petals (15-30 mm) and 5 sepals (8-19 mm) on stalks originating from leaf bases. Water purslane: inconspicuous, stalkless, located in leaf base, 4 greenish outer sepals (1.1-2 mm), no petals.
Fruit: Water primrose: capsules, 3 cm long, hang on long stalks (to 6 cm) and contain many small seeds. Water purslane: 5 mm long four-sided capsules are upright on tiny stalks and contain many tiny seeds.
Root: Fibrous roots originate from lower stem joints and often trail into the water. Water primrose also produces white spongy root-like structures that hang in the water.
Propagation: Seeds; plant fragments.
Importance of plant: Provides food for muskrats and waterfowl. Water purslane is used in water gardens and has medicinal uses.
Distribution: Water primrose: South America, southern U.S., introduced to Europe and northern North America. Water purslane: nearly worldwide.
Habitat: Margins of lakes, ponds, ditches, and streams.
May be confused with: Water primrose is difficult to distinguish from other species of Ludwigia which may be introduced. Water purslane when not in flower or fruit is easily confused with other opposite leaved wetland plants such as American brooklime (Veronica americana), Lythrum portula, or Rotala ramosior.
Line Drawings: Ludwigia palustris
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