Persicaria perfoliata is a synonym for Polygonum perfoliatum, a species of flowering plant in the buckwheat family. Common names include mile-a-minute weed, devil's tail, giant climbing tearthumb, and Asiatic tearthumb. It is a trailing herbaceous annual vine with barbed stems and triangular leaves. It is native to most of temperate and tropical eastern Asia, from eastern Russia in the north down to New Guinea and India in the south.
Persicaria perfoliata has a reddish stem that is armed with downward pointing hooks or barbs which are also present on the underside of the leaf blades. The light green leaves are shaped like an equilateral (equal-sided) triangle and alternate along the narrow, delicate stems. Distinctive circular, cup-shaped leafy structures, called ocreas, surround the stem at intervals. Flower buds, and later flowers and fruits, emerge from within the ocreas. Flowers are small, white and generally inconspicuous. The fruits are attractive, metallic blue and segmented, each segment containing a single glossy, black or reddish-black seed.
Persicaria perfoliata as a weed generally colonizes open and warm areas, along the edges of woods, wetlands, stream banks, and roadsides, and uncultivated open fields, resulting from both natural and human causes, dense wooded areas where the overstory has opened up increasing the sunlight to the forest floor. Natural areas such as stream banks, parks, open space, road shoulders, forest edges and fence lines are all typical areas to find P. perfoliata. It also occurs in environments that are extremely wet with poor soil structure. Available light and soil moisture are both integral to the successful colonization of this species. It will tolerate shade for a part of the day, but needs a good percentage, 63-100% of the available light. The ability of P. perfoliata to attach to other plants with its recurved barbs and climb over the plants to reach an area of high light intensity is a key to its survival. It can survive in areas with relatively low soil moisture, but demonstrates a preference for high soil moisture.
The first records of Persicaria perfoliata in North America are from Portland, Oregon (1890) and Beltsville, Maryland (1937). Both of these sites were eliminated or did not establish permanent populations of the species. However, the introduction of P. perfoliata somewhere between the late 1930s and 1946 to a nursery site in Stewartstown, York County, Pennsylvania produced a population of this plant that did become established in the wild. It is speculated that the seed was spread with Rhododendron stock. The owner of the nursery was interested in the plant and allowed it to reproduce; subsequent efforts to eradicate it were not successful. The distribution of P. perfoliata has radiated from the York County site into neighboring states. Fifty-five years after its introduction, the range for this plant in the United States had extended as far as 300 miles (480 km) in several directions from the York County, Pennsylvania site.
Persicaria perfoliata is primarily a self-pollinating plant (supported by its inconspicuous, closed flowers and lack of a detectable scent), with occasional outcrossing. Fruits and viable seeds are produced without assistance from pollinators. Vegetative propagation from roots has not been successful for this plant. It is a very tender annual, withering with a slight frost, and reproduces successfully until the first frost. Persicaria perfoliata is a prolific seeder, producing many seeds on a single plant over a long season, from June until October in Virginia, and a slightly shorter season in more northern geographic areas. It can cover as much as 30 feet (9.1 m) in a single season, maybe even more in the southern United States.
Birds are probably the primary long-distance dispersal agents of P. perfoliata. Transport of seeds short distances by native ant species has been observed. This activity is probably encouraged by the presence of a tiny white food body (elaiosome) on the tip of the seed that may be attractive to the ants. These seed-carrying ants may play an important role in the survival and germination of the seeds of P. perfoliata. Local bird populations are important for dispersal under utility lines, bird feeders, fence lines and other perching locations. Other animals observed eating its fruits are chipmunks, squirrel and deer.
Water is also an important mode of dispersal. Its fruits can remain buoyant for 7-9 days, an important advantage for dispersing seed long distances in stream and river environments. The long vines frequently hang over waterways, allowing fruits that detach to be carried away in the water current. During storm events the potential spread of this plant is greatly increased throughout watersheds.
Hand removal of seedlings throughout the growing season is the most effective traditional control, though hardly practical for a wide-range program. Broad-spectrum herbicides, though effective, are not practical in many infested areas due to close involvement of native vegetation. A non-systemic herbicidal soap is the preferred chemical treatment, but must be reapplied throughout the season to staunch new growth.
In 2004 the USDA approved the rearing and release of Rhinoncomimus latipes, a tiny stem-feeding weevil from China. In several Persicaria-infested release sites in New Jersey heavy defoliation of the targets occurred in the space of a few years post-release. The weevil has since been found feeding on Persicaria throughout the state, even at sites intended for new releases.
In traditional Chinese medicine, Persicaria perfoliata is known as gangbangui (Chinese: 杠板; pinyin: gāngbngūi), and is thought to be useful for its diuretic, anti-inflammatory, and other effects. It may also be eaten as a sour-flavored leaf vegetable, although it has a relatively high content of oxalic acid and cannot be consumed frequently.
Persicaria perfoliata contains phenylpropanoid esters such as 6'-acetyl-3,6-diferuloylsucrose (helonioside B), 2',4',6'-triacetyl-3,6-diferuloylsucrose, 1, 2',4',6'-tetraacetyl-3,6-diferuloylsucrose, 1,2',6'-triacetyl-3, 6-diferuloylsucrose, 2',6'-diacetyl-3,6-diferuloylsucrose, 1,3,6-tri-p-coumaroyl-6'-feruloylsucroses, vanicoside A and vanicoside B.
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