North America Non-native Plant

Manyleg Knotweed

Botanical name: Polygonum polycnemoides

USDA symbol: POPO3

Life cycle: annual

Habit: forb

Native status: Non-native, reproduces and persists in the wild in the lower 48 states  

Manyleg Knotweed: An Uncommon Annual Worth Knowing About If you’ve stumbled across the name manyleg knotweed in your plant research, you’ve discovered one of the more mysterious members of the knotweed family. Polygonum polycnemoides isn’t your typical garden center find, and there’s a good reason for that – this annual ...

Manyleg Knotweed: An Uncommon Annual Worth Knowing About

If you’ve stumbled across the name manyleg knotweed in your plant research, you’ve discovered one of the more mysterious members of the knotweed family. Polygonum polycnemoides isn’t your typical garden center find, and there’s a good reason for that – this annual forb remains something of an enigma in the gardening world.

What Exactly Is Manyleg Knotweed?

Manyleg knotweed is an annual forb, which simply means it’s a non-woody plant that completes its entire life cycle in one growing season. As a forb, it lacks the woody stems you’d find on shrubs or trees, instead producing soft, herbaceous growth that dies back each winter. The plant gets its scientific name from the Greek words meaning many knees, likely referring to the jointed stems characteristic of the knotweed family.

Where Does It Grow?

This species has a rather limited presence in North America, currently documented in just two states: Idaho and New York. It’s considered a non-native plant that has established itself in these areas and reproduces without human intervention. The scattered distribution suggests this isn’t a particularly aggressive spreader, though information about its original native range remains unclear.

Should You Plant Manyleg Knotweed?

Here’s where things get interesting – and a bit frustrating for curious gardeners. While manyleg knotweed isn’t known to be invasive or harmful, there’s remarkably little information available about its garden performance, aesthetic qualities, or ecological benefits. This lack of documentation makes it difficult to recommend for most gardening situations.

Since this is a non-native species with limited ecological data, you might want to consider native alternatives that offer similar characteristics but with known benefits to local wildlife and ecosystems. Native annual wildflowers in the buckwheat family or other indigenous forbs would likely provide better support for pollinators and local wildlife.

The Challenge of Growing Unknown Plants

If you’re determined to grow manyleg knotweed, you’ll be venturing into largely uncharted territory. The specific growing conditions, care requirements, and propagation methods for this species aren’t well-documented in horticultural literature. This means you’d essentially be conducting your own garden experiment – which could be exciting for adventurous gardeners but frustrating for those seeking reliable results.

Native Alternatives to Consider

Instead of puzzling over this mysterious knotweed, consider these well-documented native options:

  • Wild buckwheat (Eriogonum species) – offers similar growth habits with known pollinator benefits
  • Native smartweeds (Persicaria species) – related plants with documented wildlife value
  • Annual wildflower mixes suited to your specific region

The Bottom Line

While manyleg knotweed might intrigue botanical enthusiasts and collectors of unusual plants, its limited documentation and non-native status make it a questionable choice for most gardens. The gardening world is full of well-researched, ecologically beneficial plants that will give you much more bang for your buck – and your time.

If you do encounter this plant in the wild, take a moment to appreciate its rarity and the mysteries that still exist in our botanical world. Sometimes the most interesting plants are the ones we can observe and wonder about, rather than necessarily bringing home to our gardens.

Manyleg Knotweed

Classification

Group

Dicot

Kingdom

Plantae - Plants

Subkingdom

Tracheobionta - Vascular plants

Superdivision

Spermatophyta - Seed plants

Division

Magnoliophyta - Flowering plants

Subdivision
Class

Magnoliopsida - Dicotyledons

Subclass

Caryophyllidae

Order

Polygonales

Family

Polygonaceae Juss. - Buckwheat family

Genus

Polygonum L. - knotweed

Species

Polygonum polycnemoides Jaubert & Spach - manyleg knotweed

Plant data source: USDA, NRCS 2025. The PLANTS Database. https://plants.usda.gov,. 2/25/2025. National Plant Data Team, Greensboro, NC USA