NL: Perzikkruid / F: Renouée persicaire
It is traditionally used in poultices to relieve rheumatic pain, to heal wounds, to arrest bleeding or in infusion to help relieve stomach ache.
There is a variety of persicaria very similar to this one, known as smartweed. It is also edible, but it is very hot in taste, so you might want to try first a tiny small piece before putting it a lot in your mouth.
Another family member of the persicaria family that I love to use in dishes is the Persicaria odorata, also known as Vietnamese coriander. It is very easy to cultivate and makes every dish taste divinely good.
Edible & Medicinal Lady’s Thumb
Lady’s Thumb - LuminEarth
As we are talking about persicarias, in the link below you will find some information on culinary uses of persicaria odorata, which looks pretty similar to Lady's Thumb, but it tastes much better:
Persicaria odorata -Kruidwis