Various species of Japanese herbaceous knotweed that spread from gardens as neophytes in the open landscape are the focus of landscape ecologists and a broad public. Because they can multiply and spread rapidly, they are now considered problematic plants because they partially displace native vegetation. These knotweed species that have migrated from Asia include Sakhalin knotweed (Fallopia sachalinensis), Japanese perennial knotweed (Fallopia japonica or Polygonum cuspidatum), and hybrids of both species.
Occurrence and cultivation of Japanese perennial knotweed.
Perennial knotweed forms a dense closed stand. This characteristic allowed the herbaceous knotweed to become a popular ornamental plant, with which even shaded areas of large gardens could be quickly landscaped. Japanese knotweed belongs to the Polygonaceae (knotweed family), of which numerous native species are also known. Its native range in East Asia is China, Japan and Korea. Fallopia japonica was introduced over a hundred years ago as an ornamental plant, forage plant and bee pasture. The stems of this perennial hardy plant, which can grow several feet tall, bear decorative large oval leaves. Perennial knotweed forms a dense closed stand that does not allow undergrowth. These characteristics allowed herbaceous knotweed to become a popular ornamental plant that could be used to quickly green even shaded areas of large gardens. Japanese knotweed reproduces mainly vegetatively through rhizomes, which are strong storage roots. This favors its uncontrolled spread.
Effect and application
Landscape managers strive to stop the spread of the invasive plant. Partly because this is proving difficult, there are various approaches to using the products of the fast-growing plant and thereby decimating the population. The plant produces a lot of biomass in a short time. This may allow it to be used as an energy crop. There is already a cultivated form under discussion for this purpose. Various recipes should make the use of the wild form for nutrition attractive. In Japanese cuisine, there are several traditional preparations that use the knotweed, called “itadori” there. Most often, the tender shoots are used. They are peeled and boiled. Then they are soaked in water and salt to preserve them for a while. When the water is poured off again, it removes some of the oxalic acid from the vegetable. Itadori is used, for example, together with other vegetables to fill spring rolls or in the preparation of sushi. In traditional German cuisine, the shoots of knotweed can be used in a similar way to rhubarb. Their sour taste and oxalic acid content suggest similar preparation methods. People who enjoy wild herbs and creative recipes therefore use knotweed, for example, as an ingredient in relishes, compotes, jams, cakes, and lemonades. As a vegetable, the young, sour-tasting stalks are most often prepared. The preparation methods are similar to those of asparagus. Because they are hollow, thick young stalks can even be stuffed sweet or savory. The tender leaves and fresh root shoots in autumn are also edible as vegetables. Baked in beer batter, in a casserole or steamed in a vegetable stir-fry, Japanese knotweed helps provide the body with vitamins, minerals and phytochemicals. Its reservatol content is particularly significant. The secondary plant substance belongs to the polyphenols. These are considered to be effective antioxidants and radical scavengers which, together with vitamins, have a mutually reinforcing effect. Because they prevent cells from being damaged by aggressive oxygen molecules, they strengthen the immune system. Reservatol is also said to reduce the risk of developing arteriosclerosis and cancer. In diabetes, eating knotweed has a beneficial effect on blood sugar levels. However, older stalks should not be used because they contain too much oxalic acid.
Health significance, treatment and prevention.
The beneficial effects of Japanese knotweed for humans and also for plant diseases have been known for a long time. It is considered to inhibit bacteria, viruses and fungi. It improves blood pressure, can relieve pain and purify the blood. Used are all parts of the plant.Knotweed liquid manure, for example, prevents mold infestation of lettuce and strawberries as a plant protection product. It can also be used effectively against fungal diseases such as powdery mildew and late blight in tomatoes. In Asia, the plant is used to promote circulation, detoxify and as a diuretic. European herbal medicine recommends Japanese knotweed as a vegetable to promote the body’s resistance. It is said to have a life-prolonging effect due to the positive effect of the reservatol on the metabolism and the process of aging. In the laboratory, it has been shown to have an inhibitory effect on cancer cells. The plant active ingredient emodin, which is also contained, influences an enzyme that plays a role in sugar metabolism. The beneficial effect on diabetes can be attributed to this. It also has a mild laxative effect. Other uses include high blood pressure, menstrual cramps, fever and fungal diseases. Due to their tannic acid content, compresses made from fresh crushed leaves or roots can have a beneficial healing effect on skin diseases. That is why they are used for inflammations and wounds. The plant extract may manage to penetrate the protective film of acne bacteria. As a result, they can be better combated. Traditional Chinese medicine and Indian Ayurvedic medicine mainly process the roots of Japanese knotweed into extracts or powders. People suffering from rheumatism, gout, osteoarthritis and impaired kidney function may only take small amounts of Japanese knotweed. If the excretory function of the kidney is impaired, oxalate crystals may form in the form of kidney stones. Pouring away the cooking water and eating fiber-rich foods at the same time reduces the absorption of oxalic acid.
