Store › Japanese Knotweed (Polygonum cuspitadum) Image 1 of 1 Japanese Knotweed (Polygonum cuspitadum) from $23.95 Japanese Knotweed single herb tincture. Size: Select Size 100mL 250mL 500mL 1000mL Add To Cart Added! Japanese Knotweed single herb tincture.