Flower profile
Pink knotweed
Persicaria capitata
Pink knotweed (Persicaria capitata) is a low shrub in the Polygonaceae family, introduced in the lower 48 states, blooming mostly January–May across the U.S.
Pink knotweed is a wildflower that USDA PLANTS lists as introduced in the lower 48 states. In Hawaii it's most often seen in bloom in January–September.
*iNaturalist research-grade observations, as of October 17, 2026.
On our lists for: Hawaii
Quick look
Persicaria capitata, the pink-headed persicaria, pinkhead smartweed, pink knotweed, Japanese knotweed, or pink bubble persicaria, is an Asian species of plants in the genus Persicaria within the Polygonaceae family. It is native to Asia and grown as an ornamental in other countries. It has become naturalized in Australia, South Africa and a few scattered locations in the Americas.
- It belongs to the Polygonaceae family. iNaturalist
- USDA PLANTS describes it as an herb (forb) / a subshrub with a perennial life cycle. USDA PLANTS
- USDA PLANTS lists it as introduced in the lower 48 states and records it in 4 states. USDA PLANTS
- NatureServe lists it as not native to Hawaii. NatureServe
- In Hawaii, most iNaturalist sightings of it in flower come in January–September. iNaturalist
- iNaturalist has 1,726 research-grade sightings of it in Hawaii, ranking #21 among the 118 flowers on our Hawaii list. iNaturalist
When does it bloom?
In Hawaii, most flowering sightings come in January–September.
Conservation status
- Federal (U.S. ESA)
- Not listed No U.S. Endangered Species Act listing in the USFWS ECOS database. USFWS ECOS
- NatureServe global
- GNR Not yet ranked worldwide. NatureServe
- Hawaii
- Not listed Not on Hawaii threatened and endangered plants (HAR 13-107; the state list follows the federal list), DLNR Division of Forestry and Wildlife. NatureServe: SNA, not applicable (usually because it isn't native there) in Hawaii. HAR 13-107
- Rare elsewhere
- No other U.S. state ranks it S1, S2, SH or SX.
Checked October 17, 2026. Rankings and lists can change, so follow the links for the latest.
Can you eat it?
None of the sources we checked (NC State Extension (no page for this plant), USDA PLANTS) say whether it's edible or poisonous for people.
It isn't on the ASPCA plant list.
🌿 Never eat a wild plant unless you're certain of its ID; this isn't medical advice. Worried about a person? Call Poison Control at 1-800-222-1222. Worried about a pet? Call your vet.
Where does it grow?
USDA PLANTS records pink knotweed in 4 states.
recorded by USDA PLANTS on our state lists not recorded
See the full list of states
California, Hawaii, Louisiana, Oregon.
Hawaii counties with USDA records: Hawaii.
Names, range and relatives
Native status by region (USDA PLANTS): Hawaii: Introduced; Lower 48 states: Introduced.
County records: USDA PLANTS lists it in 7 counties across 4 states; the most are in California (4), Hawaii (1), Louisiana (1).
Other Persicaria on Bloomipedia (5): American jumpseed, Low smartweed, Mile-a-minute weed, Water smartweed, Spotted lady's thumb.
More from the Polygonaceae family (21 on Bloomipedia; most observed first): California buckwheat, Japanese knotweed, Sulfur buckwheat, Desert trumpet, American bistort, Cushion buckwheat, Devil's spineflower, Parsnipflower buckwheat.
More Hawaii flowers
Sources
- USDA, NRCS. PLANTS Database, profile POCA21.
- iNaturalist, Persicaria capitata: taxonomy, research-grade observation counts and “Flowering” annotations, retrieved October 17, 2026.
- Wikipedia, Persicaria capitata (lead quoted under CC BY-SA 4.0).
- Hawaii: Hawaii threatened and endangered plants (HAR 13-107; the state list follows the federal list), DLNR Division of Forestry and Wildlife.
- Hawaii: Hawaii noxious weed list (HAR 4-68).
- USFWS, ECOS species database (ESA listing check), October 17, 2026.
- NatureServe Explorer, Persicaria capitata (global and state ranks).
- Edibility and toxicity: no source found (marked "not well documented").
- Photo: florawhite via iNaturalist · CC BY 4.0 · resized.