Family Name: Polygonaceae

French Name: Renouée du Japon

This plant is native to East Asia predominately Japan, Taiwan and northern China.

In its natural habitat it has predator plant louse to keep it under control. Unfortunately elsewhere it has earned the reputation as the world’s worst invasive species. More commonly known as Japanese Knotweed.

We so do not need the knotweed!

What’s the problem?

Well those little louse critters unfortunately, are also non-native to the rest of the world too. So Japanese knotweed is causing a whole host of problems. It is outcompeting native flora and a contributor to river bank erosion which increases the likelihood of flooding.

In the UK the plant has caused significant delays and cost to development and structural damage. In fact in some cases mortgages have been refused where it has been found in gardens. You can begin to see why we so do not need the knotweed!

Where can you find it?

It is now becoming common in urban areas, on waste land, railways, road sides and river banks. When back in Devon last September I was horrified to find it growing along an estuary where I often went herb walks. In the UK they are attempting to introduce the louse in the hopes of controlling the plant.

I have now found it growing on the riverbank here in France, some three kilometres from where I live. Apparently in the Parc de Saint Périer, Morigny-Champigny, Essonne (south of Paris) they are working with goats to control plant growth.

Medicinal Uses:

I remembered some years back it mentioned in a class or lecture that it did indeed have medicinal properties.

Use in TCM…

Known as Hu Zhang in China. The dried root and leaf are utilised. It apparently has a bitter taste. Energetically described cold and dry.

In traditional Chinese medicine it is utilised to eliminate damp heat and for pain relief. Some recommended conditions include rheumatoid arthritis, trauma injuries, bronchitis, pleurisy and other damp heat lung infections.

Use in Japan…

Wild foraged as a wild edible spring vegetable in Japan. Known as Itadori which apparently means ‘pain relieving’. In addition to use as a medicinal in some areas.

a bit of science…

Constituents include anthraquinones and anthraglycosides primarily emodin. In addition there are tannins and resveratrol. Emodin and resveratrol have shown anti-tumour activity in research.

… the future

In conclusion it seems highly unlikely Japanese knotweed will ever be eradicated. Resilient to cutting. Roots can be 10 feet down and some 23 feet across. Furthermore even the tiniest piece of root remaining can return.

For the moment we so do not need the knotweed. It is hoped a way of controlling this plant is discovered before it outcompetes some of our native medicinals. And causes other damage.

Hopefully a way of controlling growth will be discovered. Perhaps then it may well become a useful medicinal ally.

Finally, I would advise against use as a medicinal in countries where it is non native. It is probable there is contamination with pesticides in the role of control.