Polygonum californicum

California knotweed

Family: Polygonaceae · Type: annual · Native

California knotweed is a California native annual found in northwestern California, Cascade Range, Sierra Nevada, Central Valley, and southwestern Mountain Provinces in open places, including serpentine habitats, at elevations of 40 to 1,200 meters. Flowering from May to October, this plant produces delicate white to pink flowers with elliptic lobes in small axillary clusters. Growing with wiry, green stems 4 to 40 centimeters tall that are slightly angled and papillate-scabrous, it has an erect or widely spreading growth habit. Its linear leaves are extremely narrow, measuring 5 to 25 millimeters long and only 0.5 to 2 millimeters wide, with margins rolled under and a mucronate or weakly spine-tipped apex. The fruit is a shiny brown, narrowly elliptic structure 1.8 to 2.2 millimeters long.

Habitat: Open places (including serpentine)

Bloom period: May-Oct

Elevation: 40-1200 m

Bioregions: NW, CaR, SN, GV, sw MP

California counties: Mendocino, Butte, Tuolumne, Napa, Shasta, Lake, El Dorado, Placer, Amador, Fresno, Tehama, Madera, Mono, Siskiyou, Tulare, Yolo, Yuba, Sacramento, Calaveras, Glenn, Mariposa, Nevada, San Francisco, San Joaquin, Stanislaus, Sutter, Trinity, Sonoma, Humboldt, Lassen, Plumas

Data from The California Species Project — 14,000+ California species with verified data from CNPS, CDFW, USFWS, Jepson eFlora, Cal-IPC, and more.