Polygonum polygaloides subsp. esotericum
Modoc county knotweed, Modoc County Knotweed
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Family: Polygonaceae · Type: Herb · Native
Conservation status: CNPS 1B.3
Polygonum polygaloides subsp. esotericum (Modoc county knotweed) is a native California herb in the Polygonaceae family.
Modoc county knotweed is a rare (CNPS 1B.3) California native annual found in the Modoc Plateau near Goose Lake and Sierra Valley in seasonally wet places and pinyon/juniper woodland at elevations around 1,500 meters. Flowering from June to August, this delicate plant produces white to pink flowers in narrow cylindric clusters 2 to 10 millimeters long. Growing with slender stems 5 to 12 centimeters tall, it forms compact, low-growing populations in seasonal wetland habitats. Its small leaves have appressed bracts 4 to 8 millimeters long with prominent green veins and rigid lance-elliptic shapes. The fruit is a dark-brown, lanceolate seed 2 to 2.5 millimeters long with a subtle net-like surface texture.
Habitat and range
Habitat: Vernal pools, seasonally wet places, pinyon/juniper woodland
Elevation: +- 1500 m.
California counties: Modoc, Sierra, Plumas, Shasta
Bloom period
Polygonum polygaloides subsp. esotericum blooms Jun-Aug.
Conservation status
CNPS 1B.3
How to tell it apart
vs Euphorbia: Polygonum has swollen stem joints with papery sheaths; Euphorbia has milky sap when broken.; vs Persicaria: Hold node sheaths to light—Polygonum's are translucent and split; Persicaria's are opaque and intact.; vs Eriogonum: Polygonum has papery sheaths at nodes; Eriogonum has flowers in cup-like involucres.; vs Acmispon: Polygonum has swollen stem nodes; Acmispon has compound leaves with 3-5 leaflets.; vs Atriplex: Polygonum has papery stem sheaths; Atriplex has mealy or scurfy coating on leaves.
Frequently asked questions
Is Polygonum polygaloides subsp. esotericum native to California?
Yes. Polygonum polygaloides subsp. esotericum is native to California (recorded as native).
When does Polygonum polygaloides subsp. esotericum bloom?
Polygonum polygaloides subsp. esotericum blooms Jun-Aug.
Where in California does Polygonum polygaloides subsp. esotericum grow?
Polygonum polygaloides subsp. esotericum occurs in Modoc, Sierra, Plumas, Shasta, at elevations of +- 1500 m..
What plant family does Polygonum polygaloides subsp. esotericum belong to?
Polygonum polygaloides subsp. esotericum is in the Polygonaceae family, genus Polygonum.
Is Polygonum polygaloides subsp. esotericum rare or endangered?
Polygonum polygaloides subsp. esotericum carries California Rare Plant Rank 1B.3, state rank S3.
Related species
Other California species in the same genus, family, or bioregion.
Sources: Jepson eFlora · CalPhotos · CDFW CNDDB
Last updated 2026-10-07
Data from The California Species Project — 14,000+ California species with verified data from CNPS, CDFW, USFWS, Cal-IPC, and more.