Japanese knotweed, « the tiger’s cane »

Hu Zhang reads « the tiger’s cane ». Li Shizhen explained it in eight characters: the cane is its stem, hollow, upright and jointed like bamboo; the tiger is its red and purple speckles. This tall perennial, one to three metres high, grows on damp ground, at woodland edges and along streams, and it is so robust that outside China it has become one of the most stubborn invasive plants in Europe. The rhizome and roots are used, thick, heavy and firm, with a yellowish-brown cut clearly marked with radiating lines. In the warm months, it was once boiled with licorice: an amber-coloured drink with a pleasant taste, which people drank more readily than tea.

Clearing Heat and Dampness

In Traditional Chinese Medicine, knotweed is slightly cold and bitter. Bitterness does two things at once: it dries Dampness and makes things descend; with neither sweetness nor richness, it nourishes nothing, it takes away. It is associated with the Liver and the Gallbladder, where tradition places what becomes congested and stagnates, and with the Lung, through which it makes things descend again. Its primary action is to clear Heat and let Dampness flow out: when the two mingle in the Liver and the Gallbladder without finding an exit, it opens one for them downwards. It also eases the passage of stools, far more gently than its relative, Chinese rhubarb.

A cold plant that makes the Blood circulate

This is what sets it apart: most plants that make the Blood circulate and dispel stasis are warm, this one is cold. Tradition therefore chooses it when the Blood stagnates and Heat is involved, where a warm plant would add fuel to the fire. Prepared with wine, it turns more towards the Blood and the collaterals, and its coldness is tempered. It is combined with capillary wormwood for the Liver and the Gallbladder. Modern research is looking in particular at resveratrol, of which it is the main industrial source; but a standardised extract is not the whole plant that tradition describes.