Ludwigia palustris (Water Purslane)
|Also known as:||Water Primrose, Marsh Purslane, Marsh Seedbox|
|Family:||Onagraceae (Evening Primrose)|
|Habitat:||part shade, sun; shallows, shorelines, mudflats|
|Bloom season:||July - September|
|Plant height:||3 to 12 inches|
|Wetland Indicator Status:||GP: OBL MW: OBL NCNE: OBL|
|MN county distribution (click map to enlarge):|
|National distribution (click map to enlarge):|
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Flowers are upright, bell shaped and stalkless, paired in the opposite leaf axils all along the stem. Petals are absent; the calyx is yellowish green to pinkish, about 1/8 inch across face with 4 pointed, semi-oval to triangular lobes flaring outward. The 4 stamens and single central style are both very short and disintegrate quickly.
Leaves and stems:
Leaves are simple and opposite, 1 to 1½ inches long and up to ¾ inch wide, spoon-shaped with a blunt tip, the lance to egg-shaped blade abruptly tapered to a winged stalk. Leaf color ranges from dull to bright green to reddish bronze, especially in the stalks. Surfaces are glossy smooth and edges are toothless. Stems are succulent and weak, 3 to 12 inches long, smooth and often reddish, and many branched. When out of water the plant sprawls along the ground with just the branch tips ascending (decumbent). In the water, branches ascend towards the surface with just the tips out of water. Both in the water and out, roots are continuously forming at the nodes, forming mats.
Fruit is an elongated capsule just under a ¼ inch long and half as wide with weakly 4-angled sides. When mature, seeds are visible through the thin walled chamber below the sinuses between the calyx lobes.
Water Purslane is widespread throughout the northern hemisphere and common across the entire eastern half of the US and west of the rockies. It appears to like sandy or silty soils with continual moisture as found along lakes, ponds, streams and rivers, especially those that experience seasonal fluctuations in water levels that expose shallow shorelines or sand bars. It also thrives in the shallow waters of smaller streams or springs. It is not a big waters species and is absent from most of Minnesota's 10,000 lakes, but prefers the small lakes, ponds, wetlands and associated streams and rivers in east central Minnesota and the Anoka Sandplain. It can appear suddenly in response to excavations or other disturbances in this region.
There are several species with which it can be confused. Toothcup (Rotala ramosior) is more rare but can be found growing right beside it. It has weakly 4-angled stems with erect to ascending growth, more lance elliptic leaves, and the flowers have in-turned calyx lobes with small out-turned appendages between them, the petals (when present) white. Valley Redstem (Ammannia coccinia) also has more erect stems, leaves more linear-oblong, flowers in tight clusters of up to 5 per axil, and petals that, while extremely fleeting, are obvious and pink when present. Also it is only found along the clay banks, mudflats and back waters of the Minnesota river and other western rivers. False Loosestrife (Ludwigia polycarpa) is also found in the same east central counties as L. palustris though typically more often in open sedge meadows and marshes. While the flowers are somewhat similar, it has alternate leaves that are lance linear, and grows erect rather than sprawling.
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Where to buy native seed and plants ↓
- Water Purslane plant
- more plants
- flower stamens arching to the style
- a mat of Water Purslane in shallow water
- Water Purslane on a muddy shore
- rooting at the nodes
Photos by K. Chayka taken in Anoka County. Photos courtesy Peter M. Dziuk taken in Anoka and Pine counties.
Have you seen this plant in Minnesota, or have any other comments about it?