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Polygonum amphibium - L.

Common Name Willow Grass, Water knotweed, Longroot smartweed, Water smartweed
Family Polygonaceae
USDA hardiness 4-8
Known Hazards Although no specific mention has been made for this species, there have been reports that some members of this genus can cause photosensitivity in susceptible people. Many species also contain oxalic acid (the distinctive lemony flavour of sorrel) - whilst not toxic this substance can bind up other minerals making them unavailable to the body and leading to mineral deficiency. Having said that, a number of common foods such as sorrel and rhubarb contain oxalic acid and the leaves of most members of this genus are nutritious and beneficial to eat in moderate quantities. Cooking the leaves will reduce their content of oxalic acid. People with a tendency to rheumatism, arthritis, gout, kidney stones or hyperacidity should take especial caution if including this plant in their diet since it can aggravate their condition[238].
Habitats Lakes, ponds, slow-flowing rivers and canals, also on banks by the river[17, 187].
Range Most of Europe, including Britain, temperate Asia, N. America and S. Africa.
Edibility Rating    (1 of 5)
Other Uses    (0 of 5)
Weed Potential Yes
Medicinal Rating    (2 of 5)
Care
Fully Hardy Wet Soil Water Plants Semi-shade Full sun
Polygonum amphibium Willow Grass, Water knotweed, Longroot smartweed,  Water smartweed


http://commons.wikimedia.org/wiki/File:Persicaria_amphibia_Sturm62.jpg
Polygonum amphibium Willow Grass, Water knotweed, Longroot smartweed,  Water smartweed
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Summary


Physical Characteristics

 icon of manicon of flower
Polygonum amphibium is a PERENNIAL growing to 0.3 m (1ft).
It is hardy to zone (UK) 5. It is in flower from July to September. The species is hermaphrodite (has both male and female organs) and is pollinated by Insects.
Suitable for: light (sandy), medium (loamy) and heavy (clay) soils. Suitable pH: acid, neutral and basic (alkaline) soils. It can grow in semi-shade (light woodland) or no shade. It prefers wet soil and can grow in water.

UK Hardiness Map US Hardiness Map

Synonyms

Persicaria amphibia.

Habitats

 Pond; Bog Garden;

Edible Uses

Edible Parts: Leaves  Seed
Edible Uses:

Leaves - raw or cooked. The young shoots are eaten in the spring[257]. Seed - cooked[178]. It is rather small and fiddly to utilize.

Medicinal Uses

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Astringent  Depurative  Pectoral  Poultice  Skin

The whole plant, but especially the root, is astringent, depurative, skin[145, 172, 178, 207]. An infusion of the leaves and stems has been used to treat stomach pains and children with diarrhoea[257]. The root has been eaten raw, or an infusion of the dried, pounded roots used, in the treatment of chest colds[257]. A poultice of the fresh roots has been applied directly to the mouth to treat blisters[257].

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Other Uses

Tannin

Tannin is obtained from the plant[145]. No more details, but it is likely to be from the root.

Cultivation details

A water or marsh plant growing in water up to 3 metres deep or in boggy soil[187]. This species is hardy to about -25°c[187]. Plants seem to be immune to the predations of rabbits[233]. The leaves are often attacked by the larvae of the water-lily beetle[187]. Plants can either be aquatic with floating ovate-oblong leaf-blades or a leggy marsh plant with lanceolate leaves[187]. Their stems root at the nodes wherever they come into contact with the soil[200].

Temperature Converter

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Propagation

Seed - sow spring in a cold frame. Germination is usually free and easy. When they are large enough to handle, prick the seedlings out into individual pots and plant them out in the summer if they have reached sufficient size. If not, overwinter them in a cold frame and plant them out the following spring after the last expected frosts. Division in spring or autumn. Very easy, larger divisions can be planted out direct into their permanent positions. We have found that it is better to pot up the smaller divisions and grow them on in light shade in a cold frame until they are well established before planting them out in late spring or early summer.

Other Names

If available other names are mentioned here

Found In

Countries where the plant has been found are listed here if the information is available

Weed Potential

Right plant wrong place. We are currently updating this section. Please note that a plant may be invasive in one area but may not in your area so it’s worth checking.

Conservation Status

IUCN Red List of Threatened Plants Status :

Related Plants
Latin NameCommon NameEdibility RatingMedicinal Rating
Polygonum alaskanumAlaska Wild Rhubarb21
Polygonum alpinumAlpine Knotweed, Alaska wild rhubarb21
Polygonum arenastrumSmall-Leaved Knotweed, Oval-leaf knotweed23
Polygonum aviculareKnotweed, Prostrate knotweed23
Polygonum barbatumJoint Weed11
Polygonum bistortaBistort, Meadow bistort, Snakeweed33
Polygonum bistortoidesAmerican Bistort31
Polygonum bungeanumBunge's smartweed10
Polygonum coccineumWater Smartweed10
Polygonum conspicuum 10
Polygonum convolvulusBlack Bindweed10
Polygonum divaricatum 10
Polygonum douglasiiKnotweed, Douglas' knotweed, Austin knotweed, Engelmann's knotweed, Johnston's knotweed, Large kno20
Polygonum dumetorumClimbing false buckwheat11
Polygonum equisetiforme 10
Polygonum fugax 30
Polygonum hydropiperSmartweed, Marshpepper knotweed22
Polygonum japonicumJapanese Knotweed, Mexican Bamboo, Japanese Knotweed33
Polygonum lapathifoliumCurlytop Knotweed11
Polygonum limosum 10
Polygonum longisetumOriental lady's thumb10
Polygonum maackianum 10
Polygonum manshurienseAsian Bistort01
Polygonum microcephalum 10
Polygonum minusPygmy smartweed10
Polygonum molle 21
Polygonum multiflorumHe Shou Wu, Tuber fleeceflower23
Polygonum nepalenseNepalese smartweed11
Polygonum orientalePrince's Feather, Kiss me over the garden gate22
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Author

L.

Botanical References

17200

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