Polygonum ramosissimum is a North American species of herbaceous annual plants in the buckwheat family,[2] widespread across much of Canada and the United States, where it is commonly called bushy knotweed.

[3] It is susceptible to downy mildew caused by the oomycete species Peronospora americana.

The greenish-yellow, rarely pink or white marked flowers, are on pedicels that are longer than the calyx.

The seeds are produced in fruits called achenes, which are egg-shaped, dark brown and around 3 mm (0.12 in) long.

Polygonum ramosissimum has great morphological variability,[6] which is notable on the same plant, between flowers and fruits produced early in the blooming season verses those produced late in the season, plants also show great variation over geographical areas.