Japanese Knotweed: From Invasive Weed to Resveratrol Source
on October 27, 2026

Japanese Knotweed: From Invasive Weed to Resveratrol Source

Few plants have a worse reputation than Japanese knotweed. In Britain it can complicate a house sale, in Sweden it is one of the hardest invasive plants to get rid of, and gardeners across Europe dread finding it.

Yet the same plant has a second life. Its root is the richest natural source of resveratrol known, and it is where most of the world's supplement-grade resveratrol comes from, including ours.

How it got here

Japanese knotweed (Reynoutria japonica, also called Fallopia japonica or Polygonum cuspidatum) is native to Japan, China and Korea. In Japan it grows on volcanic slopes and is not considered a pest.

Its route to Europe ran through one man: Philipp Franz von Siebold, a German doctor and botanist who collected plants while posted at the Dutch trading station in Japan. Back in Europe he set up a commercial nursery in Leiden in 1840 and sold knotweed as a prized ornamental. It even won a gold medal from a horticultural society in Utrecht.

In August 1850, Siebold sent a specimen to Kew Gardens in London. Victorian gardeners loved its bamboo-like stems, and by 1869 it was widely sold across Britain. Remarkably, the knotweed now found across the UK is believed to descend from that one female plant. It spreads almost entirely through its roots, not seed.

Sweden got it the same way. Known here as parkslide, it arrived as an ornamental for parks and gardens and has since spread widely.

Why it became a problem

Outside its native range, knotweed has no natural enemies. Its underground rhizomes reach several metres from the parent plant, and a piece the size of a thumbnail can start a new stand. It pushes through cracks in paving and drains and crowds out native plants.

The twist: a root full of resveratrol

The toughness that makes knotweed so hard to kill also makes it chemically interesting. Plants produce resveratrol as a defence compound, and knotweed's root stores it in quantities food plants cannot match.

One laboratory analysis measured 0.59 mg of trans-resveratrol per gram of knotweed root. That is about five times the level in peanut root measured in the same study. A single gram holds as much as a third of a litre of average red wine.

The root is not new to people, either. In traditional Chinese medicine it is known as Hu Zhang (虎杖), and the dried root is listed in the Pharmacopoeia of the People's Republic of China. Alongside resveratrol, it contains polydatin (a sugar-bound form of resveratrol) and anthraquinones such as emodin, which matters when it comes to making a supplement.

From root to supplement

Turning knotweed root into a supplement is about concentrating the one compound you want and leaving the rest behind. The root is dried, extracted and purified to isolate trans-resveratrol.

Two things need to stay out:

  • Emodin. Knotweed root naturally contains this anthraquinone. European food safety assessors found that emodin is genotoxic in laboratory tests, and the EU moved to restrict it in food in 2021. A well-made extract should contain next to none.
  • PAHs (polycyclic aromatic hydrocarbons). These contaminants can form when plant material is dried or heated, and they are regulated in botanical supplements.

How we do it at IDUN. Our trans-resveratrol comes from Japanese knotweed root. It is made into a liposomal liquid in Germany by PlantaCorp, and every batch is tested for PAH and emodin. Each serving of IDUN Liposomal Resveratrol contains 100 mg of trans-resveratrol.

There is something satisfying about it: a plant that much of Europe spends a fortune fighting, put to good use.

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