// SPECIES PROFILE · PERENNIAL · NATIVE

Water knotweed

Polygonum amphibium

Water knotweed (Polygonum amphibium) is a perennial in the — family. Native range includes AR, KS, MO, OK. Hardy in zones 1a–11a. Blooms Jun–Sep.

// QUICK FACTS

Family: —
Group: perennial
Native range: Native to 47 U.S. states, including AK, AR, AZ, CA, CO, CT…
USDA hardiness: Zones 1a–11a
Mature size: —
Sun: Full sun
Water: High · moisture-loving
Bloom: Jun–Sep
Wildlife value: Pollinator and wildlife support
Ecological role: native species profile

Water knotweed (Polygonum amphibium) — *Polygonum amphibium* — Water knotweed. Photo by Svdmolen via Wikimedia Commons (CC BY 2.5).

Field Notes

[ growing · ecology · siting · care ]

Water knotweed (Polygonum amphibium) is a perennial in the — family. Native range includes AR, KS, MO, OK. Hardy in zones 1a–11a. Blooms Jun–Sep.

Why it's on this list: native species profile. Native-range data from the Lady Bird Johnson Wildflower Center (NPIN), cross-checked against iNaturalist observations. Part of Rooted Revival's regional native plant catalog — true natives for Oklahoma, Arkansas, Missouri and Kansas.

Companion Planting

[ guild · polyculture · cross-layer pairings ]

In the same native range, water knotweed pairs naturally with: Lady Fern (Athyrium filix-femina), Wild Strawberry (Fragaria virginiana), Yarrow (Achillea millefolium), Common selfheal (Prunella vulgaris).