Persicaria hydropiperoides (Mild Waterpepper)

Plant Info
Also known as: Swamp Smartweed
Family:Polygonaceae (Buckwheat)
Life cycle:perennial
Habitat:sun; wet; shallow water, shorelines, marshes, wet ditches
Bloom season:June - September
Plant height:2 to 3 feet
Wetland Indicator Status:GP: OBL MW: OBL NCNE: OBL
MN county distribution (click map to enlarge):Minnesota county distribution map
National distribution (click map to enlarge):National distribution map

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Detailed Information

Flower: Flower shape: 5-petals Cluster type: raceme Cluster type: spike

[photo of flowers] Slender spike-like raceme at the top of the stem and sometimes from the leaf axils in the upper plant. Spikes are ascending to erect and sometimes have a gap (interrupted) near the base. Flowers are about 1/8 inch across, greenish white to pink with 5 tepals (petals and similar sepals) and 8 pink-tipped stamens. Typically only a few flowers are open at a time.

Leaves and stems: Leaf attachment: alternate Leaf type: simple

[photo of leaves] Leaves are 2 to 8 inches long and to 1½ inches wide, narrowly to broadly lance-shaped, toothless, tapering to a pointed tip, on a stalk up to ¾ inch long. Surfaces are mostly hairless but with short appressed hairs on the veins and sometimes around the edges. The upper surface usually lacks the dark spot common on other related species.

[photo of ocreae] At the base of the leaf stalk is a brown, membranous sheath (ocrea) that extends up around the stem, with bristly hairs up to 1/3 inch long on its upper edge. The ocrea surface is hairless or variously covered in stiff hairs. Stems are simple or branching, mostly hairless or with a few stiff hairs in the upper plant, erect to sprawling and rooting at the nodes in the lower plant, potentially creating large colonies.

Fruit: Fruit type: seed without plume

Fruit is a 3-sided seed, dark brown to black, smooth and shiny.


The DNR considers Mild Waterpepper an historical species in Minnesota, though the few collections that have been made in the state have all been within the past 25 years. Its variability, especially in the degree of hairiness, may confuse it with other smartweeds that have pink, terminal spikes. The consistently 3-sided seeds most reliably distinguish it from the rest. It is also perennial, where most others are annual.

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More photos

Photos courtesy Vicky May taken in Fayetteville, Arkansas.


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