Note the "squared-off" bottom of the leaf and curved to a point tip differentiate this from other members of this genus.
Reynoutria japonica NS5769 20Aug23 PW
Fallopia japonica NS8070 30Sep2017 PW
Fallopia japonica NS5563 21Oct2018 PW
Early in the season, the bamboo-like stem is distinctive.
Fallopia japonica NS6057 28Apr2019 PW
The fingers show the larger size. The base is less truncate, more cordate.
Reynoutria x bohemica NS6958 21Sep19 PW
Reynoutria x bohemica NS6958 21Sep19 PW
The inflorescences are shorter and denser than R. japonica.
Reynoutria x bohemica NS6958 21Sep19 PW
Reynoutria sachalinensis NS7956 30Jul23
The large leaves are quite strikinng.
Reynoutria sachalinensis NS7956 30Jul23
The cordate base of the leaf is clear.
Reynoutria sachalinensis NS7956 30Jul23
Looking at the edge, the hairs can be seen, it is clearer through a hand lens.
Reynoutria sachalinensis NS7956 30Jul23
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.