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Polygonaceae family

Marshpepper Knotweed Polygonum hydropiper

Marshpepper Knotweed is an introduced annual herb, found in Alaska, Canada, and Hawaii. It grows to 1.6 ft and blooms May in part shade – shade, with black fruit.

Growing & care

USDA PLANTS · TRY
Conditions
Sources · Conditions
USDA PLANTS — Sun · Soil & moisture
USDA — SoilPH — Soil pH
USDA PLANTS (DwCA, Zenodo 17903503) — Fertility Requirement / Soil Adaptation — Fertility need · Adapts to
USDA — Temp-Min °F — Hardiness
Sun
Part shade – shade
Soil & moisture
High moisture
Soil pH
5–7.5
Fertility need
Medium
Adapts to
Coarse (sandy), Medium (loam), Fine (clay)
Hardiness
USDA zone 13+
Size & form
Sources · Size & form
USDA PLANTS (DwCA, Zenodo 17903503) — Height, Mature — Height
USDA PLANTS (DwCA, Zenodo 17903503) — Growth Rate / Spread / Growth Form / Lifespan / Active Growth Period / Seed Period — Spread · Growth rate · Growth form · Active growth
USDA PLANTS — Lifespan
TRY Plant Trait Database (CC BY 4.0) · USDA PLANTS — Foliage
USDA PLANTS (DwCA, Zenodo 17903503) — Fruit/Seed Color / Fruit Persistence — Fruit
Height
1.6 ft
Spread
None — clumping
Growth rate
Rapid
Growth form
Single crown
Lifespan
Annual
Foliage
Broadleaf · medium texture
Active growth
Summer
Fruit
Black
In the garden
Sources · In the garden
USDA PLANTS (DwCA, Zenodo 17903503) — Propagation Method / Commercial Availability — Propagate by · In the trade
USDA PLANTS (DwCA, Zenodo 17903503) — Germination (cold stratification) — Seed starting
USDA PLANTS — Seed Period — Seeds ripen
USDA PLANTS (DwCA, Zenodo 17903503) — Foliage Texture / Browse Palatability / Resprout — Resprouts if cut
Propagate by
Seed
Seed starting
No stratification needed
Seeds ripen
Summer – Autumn seed-collection / harvest window
In the trade
Routinely available
Resprouts if cut
No
Herb layer — Sits in the herb of a layered food forest or polyculture.Open guide →
derived roles
The garden year bloom → fruit → fall colour
J
F
M
A
M
J
J
A
S
O
N
D
Bloom
Bloom (the flower's colour)
Bloom · May — USDA PLANTS (DwCA, Zenodo 17903503) — BloomPeriod
When to sow · for your area

Sow timing keys off your local last- and first-frost dates.

Species characteristics from USDA PLANTS (public domain) + TRY (CC BY) — general guidance, not a guarantee for your exact site. Deer "browsing" is documented palatability, not a deer-proof claim.

Wildlife & pollinators

How pollinator value is scored →
❧ Caterpillar hosts ~58 caterpillar species

Polygonum supports ~58 caterpillar species.

Native butterfly & moth caterpillars are the base of the terrestrial food web — most songbirds rear their young almost entirely on them. As a host for native Lepidoptera this is a strong genus.

Recorded feeding on Polygonum in North America, including:

Acronicta oblinita · Smeared Dagger Moth ✦ Agrochola helvola · Flounced Chestnut ✦ Haematopis grataria · Chickweed Geometer ✦ Hypena scabra · Black Snout ✦ Melanchra picta · Zebra Caterpillar Moth ✦ Orthonama centrostrigaria · geometer (inchworm) moth ✦
+ 8 more species →
Orthonama obstipata · geometer (inchworm) moth ✦ Papaipema nebris · Stalk Borer ✦ Prochoerodes transversata · geometer (inchworm) moth ✦ Simyra henrici · owlet moth ✦ Xanthotype sospeta · Crocus Geometer Moth ✦ Agrotis subterranea · owlet moth Anticlea multiferata · Many-Lined Carpet Apantesis nais · Nais Tiger Moth
Keystone count (genus-level) from Warren II 2026 (CC0) · Tallamy host-use records. Named species (a documented Nearctic sample, not exhaustive) from NHM HOSTS (CC0). ✦ = recorded on this exact species.
Species thumbnails re-hosted from iNaturalist — Creative Commons, credited per image (hover for credit). Click any species to see it on iNaturalist. Not exhaustive; many taxa have no openly-licensed photo yet.
How we know this (1) Methods & honest limits
Photosynthesis Direct fact

A recorded categorical fact: each species is tagged C3 (standard), C4 (heat/water-efficient) or CAM (succulent, night-time CO₂ uptake) — or a facultative combination. We only show a trait card for the noteworthy C4/CAM cases; C3 is the unremarkable majority, kept in the data but not surfaced as a card.

Kattge, J. et al. TRY plant trait database — Categorical Traits Dataset (2012).
Derived values are computed from open data by a published method — labelled, cited, and never shown as a direct observation. Full methodology →
Sources for this entry (24) Open & cited
[01] Scientific name & family — USDA PLANTS (DwCA, Zenodo 17903503)
[02] Growth habit & duration — USDA PLANTS (DwCA, Zenodo 17903503)
[03] Native status & distribution — USDA PLANTS (DwCA, Zenodo 17903503)
[04] Common name — USDA PLANTS (via GBIF)
[17] Invasive / introduced status — USDA PLANTS (DwCA, Zenodo 17903503) — native status
[19] Ecological value — Warren II 2026 (CC0) · Tallamy host-use counts
[21] Photosynthetic pathway — TRY Plant Trait Database (CC BY 4.0)
[23] Caterpillar host count — Warren II 2026 (Dryad, CC0) · Tallamy host-use counts
[24] Caterpillar species — NHM HOSTS (CC0)
Spot an error or have a better photo? Every field links to its source, and the whole dataset is open.
Cite this page Open data, please attribute

PlantKey’s data is open under CC BY-SA 4.0 — free to reuse and adapt, with attribution and the same licence. Photos keep their own per-image licence + credit (see Sources above).

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