Reynoutria - Japanese Knotweeds (Fallopia)

Reynoutria japonica, Japanese Knotweed

This is the commonest and has leaves rarely > 12 cm in length, hairless on lower side and cut across (truncate) at base. Only the female plants occur in the British Isles. It is classed as an invasive species.

Reynoutria japonica x sachalinensis = R. x bohemica, Bohemian Knotweed

This is larger with leaves up to 20 cm in length. The bases are slightly curved (weakly cordate) and less cut off at the base. The lower size has short stout hairs on lower side. Fold the leave over and look across the fold with hand lens, they can be hard to spot. Both male and female plants occur.

Reynoutria sachalinensis Giant Knotweed

Has leaves leaves often over 20 cm in length which are distinctly cordate (heart shaped) at base with scattered, long flexuous hairs on the lower side. Fold the leave over and look across the fold with hand lens, they can be hard to spot. Both male and female plants occur.

These species were previously known as Fallopia which was renamed as Reynoutria in Stace 4th Ed. However, the genera can hybridise.