Polygonum is a genus of about 130 species of flowering plants in the buckwheat and knotweed family Polygonaceae. Common names include knotweed and knotgrass. In the Middle English glossary of herbs Alphita, it was known as ars-smerte. There have been various opinions about how broadly the genus should be defined. For example, buckwheat has sometimes been included in the genus as Polygonum fagopyrum. Former genera such as Polygonella have been subsumed into Polygonum; other genera have been split off.
Polygonum arenastrum, commonly known as equal-leaved knotgrass, is a summer annual flowering plant in the knotweed family Polygonaceae. Other common names include common knotweed, prostrate knotweed, mat grass, oval-leaf knotweed, stone grass, wiregrass, and door weed, as well as many others. It is native to Europe and can be found on other continents as an introduced species and a common noxious weed. Knotweed was first seen in North America in 1809 and is now seen across much of the United States and Canada.
Persicaria lapathifolia, known as pale persicaria, is a plant of the family Polygonaceae. It is closely related to Persicaria maculosa and as such is considered a weed in Britain and Europe. Other common names for the plant include pale smartweed, curlytop knotweed, and willow weed. It is a species complex made up of a great many varying forms, sometimes considered varieties. The environment also has a strong influence on the morphology of an individual plant.
Polygonum ramosissimum is a North American species of herbaceous annual plants in the buckwheat family, 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.
Polygonum bolanderi is an uncommon California species of flowering plant in the buckwheat family known by the common name Bolander's knotweed.
Polygonum californicum is a species of flowering plant in the buckwheat family known by the common name California knotweed. It is native to the west coast of the United States from Washington, Oregon, and northern and central California in the Coast Ranges and Sierra Nevada foothills as far south as Napa and Tulare Counties. It can be found in many types of open habitats.
Polygonum marinense is a rare North American species of flowering plants in the buckwheat family known by the common name Marin knotweed. It is endemic to California, where it is known from just a few locations north and east of San Francisco Bay.
Polygonum minimum is a species of flowering plant in the knotweed family known by the common name broadleaf knotweed. It is native to much of western North America where it can be found in mountainous regions. It grows in the subalpine and alpine climates of high mountain ranges from Alaska to Arizona and New Mexico.
Polygonum polygaloides is a North American species of flowering plants in the buckwheat family known by the common names milkwort knotweed and polygala knotweed. It is native to much of western North America, where it can be found in many types of moist habitat. It is a variable species, usually divided into a number of subspecies.
Polygonum shastense is a species of flowering plant in the knotweed family known by the common name Shasta knotweed. It is native to sections of southwestern Oregon, northwestern Nevada, and northern and central California, where it grows in rocky and gravelly mountainous habitat up to 3300 meters (11,000 feet) elevation. It is most common in the Sierra Nevada. The species name refers to its occurrence on Mount Shasta in Shasta County, California.
Bistorta bistortoides is a perennial herb in the buckwheat and knotweed family Polygonaceae. The species name remains unresolved.
Erigeron tenuis is a North American species of flowering plant in the family Asteraceae known by the common name slender-leaf fleabane. It is native to the south-central part of the United States from central Texas to the Florida Panhandle, north as far as Missouri and Kansas.
Polygonum achoreum, common names Blake's knotweed, leathery knotweed or striate knotweed, is a North American species of plants in the buckwheat family. It is widespread across much of Canada and the northern United States.
Polygonum argyrocoleon, common names silver-sheath knotweed and Persian knotweed, is an Asian species of plants in the buckwheat family. It is native to Siberia, western China, Central Asia, and the Middle East. It has also become naturalized in parts of the United States, primarily the Southwest, and northwestern Mexico.
Polygonum majus is a North American species of flowering plant in the buckwheat family known by the common name wiry knotweed. It grows in the western United States and western Canada, from British Columbia south as far as the Sierra Nevada of northwestern Inyo County in California, east as far as Montana. Knotweed is a spreading, wiry annual weed that rarely grows higher than a few inches. The leaves are tiny, oblong, bluish-green, and 14 inches broad and 1 inch long. The flowers are tiny and unobtrusive, whitish-green in colour, and appear in the leaf axils in the fall. Knotweed may grow into a dense mat with a diameter of up to three feet, strangling out ideal grass and plants. The branches of this evergreen plant form a strong, wiry mat that reaches barely a few centimeters above the earth. They appear constantly, and gardeners are always fighting them. We cultivate the soil by tilling and enriching it. We plant our flowers and veggies, but the weeds make the most of our efforts. We believe we've got situation under control, but then we walk around to discover different things growing where we didn't expect it: knotweed sprawls down our walkways and up between our patio's paving stones.
Polygonum nuttallii is a North American species of flowering plant in the buckwheat family known by the common name Nuttall's knotweed. It grows in the Pacific Northwest, in British Columbia, Washington, and Oregon.
Polygonum oxyspermum is a coastal species of flowering plant in the buckwheat family. It is native to Europe, primarily along the shores of the Atlantic, the North Sea, and the Baltic Sea, from France and Ireland to Finland and Russia. It is also naturalized in eastern Canada and in the US State of Maine.
Polygonum patulum, called tree hogweed, is a species of flowering plant in the knotweed family. It is native to the Mediterranean region, eastern Europe, the Caucasus, Siberia, Central Asia, Mongolia, and the Province of Xinjiang in northwestern China. It has also become sparingly naturalized in scattered locations in Australia and North America.
Polygonum utahense, the Utah knotweed, is an unresolved name for a putative North American species of plants in the buckwheat family. It has been found only in the States of Utah and Arizona in the southwestern United States.
Slender knotweed can refer to multiple plants:
