Polygonum ramosissimum is a North American species of herbaceous annual plants in the buckwheat family,[1] widespread across much of Canada and the United States, where it is commonly called bushy knotweed.[2] It is susceptible to downy mildew caused by the oomycete species Peronospora americana.[3]
Polygonum ramosissimum has erect stems growing 30to (sometimes to 200 cm or 80 inches) tall, with yellowish-green to blue-green foliage. The stems are freely branched with closed flowers produced in groups of (1) 2 to 3(5) flowers in the upper ocreae of racemes that are up to 15round=0.5NaNround=0.5 long, the inflorescences are spike-like. The greenish-yellow, rarely pink or white marked flowers, are on pedicels that are longer than the calyx. The calyx is around 3mm long and 5-parted with the outer three sepals longer than the inner sepals. The seeds are produced in fruits called achenes, which are egg-shaped, dark brown and around 3mm long. The achenes also have a smooth shiny surface. The late season achenes are larger, from 4 to 15 mm long.[4] [5]
In Maryland, the species is listed as endangered or extirpated from the state, in Pennsylvania it has been exterminated from the state, and New Hampshire lists it as threatened.[1]
