South Dakota Native Plant Research
Polygonaceae : Polygonum amphibium

Polygonaceae : Polygonum amphibium


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Family Name


Common Name

Water smartweed, Swamp smartweed, Marsh smartweed

Native American Name

Lakota: táku šašála, pšitȟóla hú iyéčheča


Polygonum amphibium is a rhizomatous perennial herb, with floating, prostrate to erect stems, growing to 2 m in length, often hairless when rooted in water or with hairs when growing on dry land. The simple, alternate leaves are 3-20 cm long, 1-8 cm, wide with entire margins, hairy to smooth surfaces, blunt-tipped or tapered to a point, slightly tapered to rounded at the base, sessile to having long petioles on aquatic forms. At the node there is a sheath that can be brown and papery to forming a green collar around the stem. The inflorescence consist of 1 or 2 spike-like racemes, 5-10 cm long, either long and slender or short and more thimble-shaped depending on whether the plant is aquatic or terrestrial. The flowers have 5 pink tepals, 4-5 mm long, with 8 unequal stamens both included and exerted, and 2 styles. The fruit is a lenticular achene 2.54 mm long. Polygonum amphibium is a variable species, with both terrestrial (var. emersa) and aquatic forms (var. stipulacea) that have been formally recognized. In South Dakota both forms can be found, sometimes in the same location, and are treated here as part of a single complex. Water smartweed blooms from June into September in wet places throughout South Dakota.

Synonyms: Persicaria amphibia, Polygonum coccineum

Additional Notes

Marsh smartweed can be a nice, if somewhat aggressive, addition to a pond or wetland garden. It can rapidly spread as their stems root at the nodes wherever they come into contact with the soil. This species acts as host plant for several moth and butterfly species and attracts bees, butterflies and moths as pollinators.

Horticulture Notes

Seed collection: Collect achenes in late summer and fall.

Germination: Fall sowing in wet ground or spring planting of sandpaper scarified or 60-day cold moist treated seed.

Vegetative propagation: New plants arise from stems that tough the ground. They can be transplanted during the growing season.

Soils: Sands, loams to clays.

Water: Medium wet to shallow standing water.

Polygonaceae : Polygonum amphibium