Practical ecological knowledge for the temperate reader.

Polygonum Sp. - Knotweed

"Habit: Annual, perennial herb to shrub. Stem: prostrate to erect, 8--16-ribbed or 4--5-angled with ribs 0 or obscure; glabrous or papillate-scabrous. Leaf: cauline, alternate, petioled or not; ocrea generally jointed to leaf, generally cylindric proximally, generally translucent distally, white or silvery, 2-lobed, glabrous, disintegrating to fibers or completely; blade linear, lanceolate, elliptic, ovate, or subround, entire. Inflorescence: axillary, terminal, generally spike-like; peduncle 0; pedicels present or 0, included in to exserted from bractlets; flowers 1--7(10). Flower: bisexual, base not stalk-like; perianth not enlarging, bell- to urn-shaped, glabrous, white or green-white to pink; perianth parts 5, fused 3--60[70]%, petal- or sepal-like, similar [or not], outer +- keeled or not, < to > inner, midveins generally a different shade or color than rest of perianth; stamens 3--8 (some staminodes or not), filaments or at least innermost free, wider at base, fused to perianth tube or not, anthers elliptic to oblong, white-yellow or generally pink to purple (orange-pink); styles (2)3, generally spreading, free or fused basally, stigmas 2--3, head-like. Fruit: included or exserted, wings 0, angles (2)3, 1 face much narrower than other (1)2 or not; tip beak-like, yellow-green, brown, or black. Seed: embryo curved."
Species In Genus: "+- 65 species: +- worldwide; sect. Duravia restricted to western North America. Etymology: (Greek: poly, many, gony, knee joint, or gone, seed, of uncertain meaning) Note: Many species of sect. Polygonum with 2 kinds of fruit, differing in germination and morphology (summer fruit brown, ovate, tubercled to smooth; late-season fruit olive-green, lanceolate, smooth, 2--5 × > summer), but of little taxonomic importance. Mature, early-season plants with leaves, flowers, fruits needed for identification. Flowers "closed" or "1/2-open" should be determined on herbarium specimens. Other taxa in TJM (1993) moved to Aconogonon, Bistorta, Fallopia, Persicaria." [Jepson]

Comment: "There is a close taxonomical relationship between Persicaria, Bistorta and Polygonum." [Personal Observation]

Local Species;

  1. Polygonum achoreum - Blake's knotweed
  2. Polygonum arenastrum - Oval-leaved knotweed
  3. Polygonum aviculare - Common knotweed [E-flora][PCBC][TSFTK]
  4. Polygonum buxiforme - eastern knotweed
  5. Polygonum douglasii - Douglas's knotweed [E-flora][PCBC]
  6. Polygonum fowleri - Fowler's knotweed [E-flora][PCBC]
  7. Polygonum minimum - leafy dwarf knotweed [E-flora][PCBC]
  8. Polygonum nuttallii - Nuttall's knotweed
  9. Polygonum paronychia - Black knotweed [E-flora][PCBC][TSFTK]

Polygonum arenastrum - Oval-leaved knotweed

Hazards: [Same as for Persicaria maculosa] [PFAF]3

Edible Uses: "Young leaves and plants - raw or cooked[105, 177]. Used as a potherb[183], they are very rich in zinc[179]. A nutritional analysis is available[218]. Seed - raw or cooked. Rather small and fiddly to utilize, they can be used in all the ways that buckwheat (Fagopyrum esculentum) is used, either whole or dried and ground into a powder for use in pancakes, biscuits and piñole[4, 55, 106, 161, 183]. The leaves are a tea substitute[183]." [PFAF]3

Other Uses: "Yields a blue dye that is not much inferior to indigo[115]. The part used is not specified, but it is likely to be the leaves. Yellow and green dyes are obtained from the whole plant[168]. The roots contain tannins, but the quantity was not given[223]." [PFAF]3

Medicinal Uses: "Knotweed is a safe and effective astringent and diuretic herb that is used mainly in the treatment of complaints such as dysentery and haemorrhoids. It is also taken in the treatment of pulmonary complaints because the silicic acid it contains strengthens connective tissue in the lungs[254]. The whole plant is anthelmintic, astringent, cardiotonic, cholagogue, diuretic, febrifuge, haemostatic, lithontripic and vulnerary[4, 7, 9, 21, 53, 147, 172, 176, 178]. It was formerly widely used as an astringent both internally and externally in the treatment of wounds, bleeding, piles and diarrhoea[4]. Its diuretic properties make it useful in removing stones[4]. An alcohol-based preparation has been used with success to treat varicose veins of recent origin[7]. The plant is harvested in the summer and early autumn and is dried for later use[9]. The leaves are anthelmintic, diuretic and emollient[218]. The whole plant is anthelmintic, antiphlogistic and diuretic[218]. The juice of the plant is weakly diuretic, expectorant and vasoconstrictor[218]. Applied externally, it is an excellent remedy to stay bleeding of the nose and to treat sores[4]. The seeds are emetic and purgative[4, 240]. Recent research has shown that the plant is a useful medicine for bacterial dysentery. Of 108 people with this disease, 104 recovered within 5 days when treated internally with a paste of knotweed[254]." [PFAF]3

Cultivation: "Succeeds in an ordinary garden soil[1] but prefers a moisture retentive not too fertile soil in sun or part shade[200]. Repays generous treatment, in good soils the plant will cover an area up to a metre in diameter[1, 4]. Prefers an acid soil[20]. Dislikes shade. Knotweed is a common and invasive weed of cultivated ground[7]. It is an important food plant for the caterpillars of many species of butterflies[30]. It also produces an abundance of seeds and these are a favourite food for many species of birds[4]. Plants seem to be immune to the predations of rabbits[233]. The flowers have little or no scent or honey and are rarely visited by pollinating insects. Self-fertilization is the usual method of reproduction, though cross-fertilization by insects does sometimes occur[4]. The plant also produces cleistogomous flowers - these never open and therefore are always self-fertilized[4]. The plant is very variable according to habitat and is seen by most botanists as part of an aggregate species of 4 very variable species, viz. - P. aviculare. L.; P. boreale. (Lange.)Small.; P. rurivacum. Jord. ex Box.; and P. arenastrum. Bor[17]." [PFAF]3

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." [PFAF]3

Polygonum aviculare; - Knot Grass



Hazards: "Abortifacient effects" [Capasso PQR]

Edible Uses:

Other Uses:

Medicinal Uses

"The medicinal parts are the herb, sometimes with the root, collected during the flowering season and dried, as well as the fresh aerial parts collected during the flowering season." [PDR]

Activities: "The whole plant is anthelmintic, astringent, cardiotonic, diuretic, febrifuge, hemostatic, in the treatment of wounds, bleeding, piles." [Abbasi WEVLH] "Knotweed has astringent properties." [PDR]

"This is an astringent, useful in diarrhoea and other such ailments (Grieve. 1931), which would include haemorrhages. A Somerset remedy for nosebleed is to rub the plant into the nostrils (Tongue. 1965). It has been used for many other ailments, as recommended by the early herbalists. There is a leechdom from the 15th century for earache, for example, using the juice in the ear, “and it shall take away the aching wondrously well” (Dawson). In Chinese medicine, the juice is used in skin diseases, and for piles (F P Smith), and also for bladder complaints (Geng Junying)." [DPL Watts]


Alleleopathic: Against Cynodon dactylon. [Cheema Alleleopathy]

Dynamic Accumulator:

Polygonum douglasii - Douglas's knotweed

Polygonum fowleri - Fowler's knotweed

Polygonum paronychia - Black knotweed (beach knotweed)

Species Mentioned;

P. viviparum.[Turner, Kuhnlein] P. bistorta, P. bistortoides, P. amphibium, P. aviculare, P. alaskanum. [Schofield] Polygonum bistortoides. P. viviparum.[Harrington] (Polygonum bistortoides, P. viviparum, P. persicaria) [Meuninck EWPUH] Water Smartweed (P. amphibium), Bistort (P. bistortoides), California Knotweed (P. californicum), Davis’ Polygonum (P. davisiae), Polygonum (P. douglasii), Leafy Dwarf Knotweed (P. minimum), Parry’s Knotweed (P. parryi), Alpine Knotweed (P. phytolacceafolium), Knotweed (P. polygaloides), Shasta Knotweed (P. shastense) [Vizgirdas WPSN]


All species contain tannins; large amounts over long periods might spark digestive upset and possible kidney damage. Skin reactions, including hypersensitivity to light, have been known to occur in some individuals. In moderate quantities, the genus is generally regarded as quite safe. [PFAF]

P. bistorta, P. douglasii, P. polystachyum, P. persicaria, P. sachalinense; 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].[PFAF]

Edible Uses

"Experimentation may be the rule for Polygonum, as none of the species is known to be poisonous. The species do, however, vary in degrees of palatability. Tannins are found in the plants, and large amounts might cause digestive upset and possible kidney damage. In moderate quantities, however, the genus is generally regarded as safe. Based on our experiments with various species, some have peppery-tasting leaves that can be used in flavoring foods. Others have starchy roots that may be eaten raw or boiled and roasted. Still others have young foliage made into good salads or potherbs. In our opinion, of all the species, Polygonum bistortoides (bistort) tastes the best." [Vizgirdas WPSN]


Added to salads and soups, and steamed as a potherb. Spring to summer.[Schofield]


Nutty and flavored like buckwheat; sprinkle them on bread and buscuit dough in place of poppy seeds. They can be dried and ground as a flour extender for making bannock and other baked goods. Late summer.[Schofield] "The seeds have been used whole or ground into flour. The seeds of Polygonum are described as a prehistoric food source and are frequently found in archaeological remains." [Vizgirdas WPSN]


Short, fleshy rhizomes were eaten.[Turner, Kuhnlein] Rhizomes of P. bistorta and P. viviparum can be roasted on campfire coals. Due to their small size, you may prefer to add a few sliced rootstocks to stir-fries (for crisp texture and an almond like flavor) rather than relying on them as a potato substitute. They are also good in soups and stews. Spring and fall.[Schofield] "A decoction of the roots can be made for a sore mouth or gums. The root can also be used as an astringent, diuretic, antiseptic, and alterative. The roots were eaten by maritime explorers to prevent scurvy." [Vizgirdas WPSN]

Other Uses


Bistort salve is applied externally for bleeding piles and itchy skin diseases. Sprinkling the root powder on a shaving cut quickly coagulates the blood; the powder blended with clay and water forms a paste used on abscesses and insect stings. [Schofield]
Since the Middie Ages, Polygonum root poultices have been applied to foul sores and bites of "serpents and venemous beasts." Sailors and explorers looked to Polygonum leaves for vitamin C to combat scurvy.[Schofield]

More Food Uses

Rhizome: Said to be starchy and slightly astringent, and, although edible raw, they are most palatable when cooked. Reported to be a choice delicacy of several Inuit tribes, who preserve them by freezing, or in seal oil. The Fisherman Lake Slave dug them in July and fried them for eating. The fresh rhizomes could be stored in underground caches. The Lime Village Tanaina of Alaska ate the roots raw, and chewed them to clean the teeth after eating fish eggs.[Turner, Kuhnlein]

For the two species: The two kinds have similar uses but the American Bistort has the advantage of producing larger rootstocks. The young leaves can be used as a potherb and are said to have a pleasingly tart taste. The rootstocks have often been used by the Indians, some tribes esteeming them highly. We ate some of the rootstocks raw and thought them starchy and rather pleasant, with no bitter taste to the rind or contents. Some of the older ones were slightly fibrous and we would recommend cooking them. It does not seem necessary to peel them, which would be difficult to do in any case, since the surface is so rough and irregular. However, we must admit this peel does not improve the appearance of the cooked product. [Harrington]

We boiled them for 40 minutes and ate them with salt, pepper and butter, peel and all. The taste was rather starchy, but very pleasant. One of us compared the flavor to that of the water chestnut of Japan. We also wrapped the rootstocks in aluminum foil and baked them for 40 minutes in an oven at 300 to 325 degrees F. When eaten with butter, salt and pepper they were judged to be an excellent food, with a sweet, pleasant, nutty taste. [Harrington]

Our two species are often abundant, the rootstocks are borne shallowly in the soil (although rather hard to dig), so they are fairly easy to secure in quantities; they are edible raw and are very palatable cooked. These plants would be excellent to try on a camping or fishing trip, and make a good emergency food in the higher elevations in the mountains. [Harrington]


"Some species of Polygonum (knotweed) contain stilbene phytoestrogens, including resveratrol." [SEHM]

Nutritional Info

Knotweed – Polygonum sp.[Turner, Kuhnlein]

Part: Bulbs Per 100 g fresh weight

Protein (g) 1.7
Calcium (mg) 11
Magnesium (mg) 33
Fat (g) 0.2
Phosphorus (mg) 44
Iron (mg) 2.3

Carbohydrate (g) 1.8
Sodium (mg) 3.8
Manganese (mg) 0.4
Crude Fiber (g) 0.6
Potassium (mg) 71
Ash (g) 0.3


"Montane meadows play important ecological roles. They break up the mixed evergreen and lower and upper montane forests, giving the landscape a quiltwork pattern and creating ecotones, areas of rich biodiversity where forest and meadow merge.The rare great gray owl forages primarily in montane meadows, and a host of other wildlife species, such as a grouse that feeds on knotweed (Polygonum spp.), regularly use and visit them. Ungulates, such as mule deer, gravitate to meadows, making these clearings opportune places for hunting.44" [Anderson TTW]

Related Sp.

"Some species of Polygonum, called "Smartweeds," have an acrid juice in the stems and leaves, but these species all have two or more flower clusters to a stem and have only a distant resemblance to our two plants. Even some of these, such as Polygonum persicaria) have been used as a salad or as a seasoning. The Japanese Knotweed (P. cuspidatum) with broad leaves cut off square at the base, is often planted as an ornamental and sometimes runs wild, even becoming weedlike. The young shoots have been cooked like asparagus and the rootstocks boiled or baked. The seeds of several kinds of Polygonum have been used as food after being parched and ground into meal but they would surely be tedious to gather in quantity." [Harrington]

"The leaf juice [of Citrus medica], combined with that of Polygonum and Indigofera is taken after childbirth." [EMNMPV.4]


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