Polygonum ramosissimum is a herbaceous annual plant species native from most of North America, were it is commonly called Bushy knotweed.

Description

Plants have erect stems growing 30 to 100 cm (sometimes to 200 cm) tall, with yellowish-green to blue-green colored 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 15 cm 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 3 mm long and 5-parted with the outer three sepals longer than the inner sepals. The seeds are produced in fruits called achenes, which are ovoid in shape, dark brown in color and around 3 mm long. The achenes also have a smooth shiny surface. The late season achenes are larger, from 4 to 15mm long.

There are a number of forms and two subspecies, that vary in flower and foliage coloration. Polygonum ramosissimum has great morphological variability, 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.

In Maryland it 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.