Ludwigia palustris (Water Purslane)
|Also known as:
|Water Primrose, Marsh Purslane, Marsh Seedbox
|Onagraceae (Evening Primrose)
|part shade, sun; shallows, shorelines, mudflats
|July - September
|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 stalkess and single in the leaf axils all along the stem. Petals are absent; the calyx is cup-shaped, yellowish green to pinkish, up to 1/8 inch (1.5 to 3.5 mm) long with 4 pointed, semi-oval to triangular lobes flaring outward. The 4 short stamens alternate with the 4 lobes of a nectary disc, with a single style in the center.
Leaves and stems:
Leaves are opposite, up to 1¾ inches (45 mm) long and about 1 inch wide, spoon-shaped with a blunt to pointed tip, the lance to egg-shaped blade abruptly tapered to a narrowly 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, 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 less than a ¼ inch (2 to 5 mm) 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. Grand Redstem (Ammannia robusta) also has more erect stems, leaves more linear-oblong, flowers in tight clusters of up to 5 per axil, petals (when present) are obvious and pink to lavender, and is primarily found along the banks, mudflats and back waters of rivers from the Red River, through the Minnesota River valley, and down the Mississippi River to about where it joins the Cannon River. 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, and, while the flowers are somewhat similar, it has alternate leaves that are lance linear, and grows more erect rather than sprawling.
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- 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
- roots forming at the nodes
Photos by K. Chayka taken in Anoka County. Photos by Peter M. Dziuk taken in Anoka and Pine counties.
Have you seen this plant in Minnesota, or have any other comments about it?