''Polygonum ramosissimum'' is a North American species of herbaceous annual plants in the

buckwheat family The Polygonaceae are a family of flowering plants known informally as the knotweed family or smartweed—buckwheat family in the United States. The name is based on the genus ''Polygonum'', and was first used by Antoine Laurent de Jussieu in 1789 ...

,''Polygonum ramosissimum''
United States Department of Agriculture plants profile, retrieved 14 July 2008 widespread across much of Canada and the United States, where it is commonly called bushy knotweed. It is susceptible to downy mildew caused by the oomycete species '' Peronospora americana''.

Description

''Polygonum ramosissimum'' has erect stems growing (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

ocrea An ochrea (Latin ''ocrea'', greave or protective legging), also spelled ocrea, is a plant structure formed of stipules fused into a sheath surrounding the stem, and is typically found in the Polygonaceae The Polygonaceae are a family of flower ...

e of racemes that are up to 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 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 long. The achenes also have a smooth shiny surface. The late season achenes are larger, from 4 to 15 mm long.Flora of North America, ''Polygonum ramosissimum'' Michaux, 1803. Bushy knotweed
/ref> ;Subspecies 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. The following names are widely recognized. *''Polygonum ramosissimum'' subsp. ''prolificum'' (Small) Costea & Tardif *''Polygonum ramosissimum'' subsp. ''ramosissimum'' In

Maryland Maryland ( ) is a state in the Mid-Atlantic region of the United States. It shares borders with Virginia, West Virginia, and the District of Columbia to its south and west; Pennsylvania to its north; and Delaware and the Atlantic Ocean to ...

, the species is listed as endangered or

extirpated Local extinction, also known as extirpation, refers to a species (or other taxon) of plant or animal that ceases to exist in a chosen geographic area of study, though it still exists elsewhere. Local extinctions are contrasted with global extinct ...

from the state, in

Pennsylvania Pennsylvania (; ( Pennsylvania Dutch: )), officially the Commonwealth of Pennsylvania, is a state spanning the Mid-Atlantic, Northeastern, Appalachian, and Great Lakes regions of the United States. It borders Delaware to its southeast, ...

it has been exterminated from the state, and

New Hampshire New Hampshire is a U.S. state, state in the New England region of the northeastern United States. It is bordered by Massachusetts to the south, Vermont to the west, Maine and the Gulf of Maine to the east, and the Canadian province of Quebec t ...

lists it as threatened.

References

External links

photo of herbarium specimen at Missouri Botanical Garden, collected in Missouri in 1918
{{Authority control ramosissimum Flora of Canada Flora of the United States Plants described in 1803 Taxa named by André Michaux