[2][3] Polygonum bidwelliae is endemic to California, where it is known from the northern Sacramento Valley and adjacent slopes of the southernmost Cascade Range in Butte, Shasta, and Tehama Counties.

[4] It grows in chaparral, woodland, and grassland habitat on volcanic soils.

[5] Polygonum bidwelliae is an annual herb producing an erect green, wiry, angled stem reaching 20 centimeters (8 inches) in height.

The leaves have relatively large stipules which form ochrea that sheath the stem, sometimes hiding the leaf bases.

Bright pink flowers occur in upper leaf axils.