This plant grows even taller than Japanese Knotweed and can hybridise with the same producing Fallopia x Bohemica, but there are marked differences between the two plants. Less common, as it was grown in fewer gardens, so fewer opportunities for escape, it can be found in some scattered areas around coastal sites, including on the Western Isles.
It grows tall and bushy, with reddish stems branching in the upper part. The leaves are much longer than Japanese Knotweed, growing up to 30cm in length, and are more rounded at the base and heart shaped rather than triangular. Smaller leaves can be oval. Leaves are pointed at the tip with purplish veins. On the underside of leaves a few scattered hairs can be found. The leaves tend to have a drooping habit, and the stems themselves droop from their knotted leaf nodes at the top of the plant.
Flowers grow in dense clusters on shorter, branched axillary stalks from the leaf nodes, and are greenish rather than the off-white of Japanese Knotweed.
Giant Knotweed is native to an island called Sakalin, off the coast of Japan, and, like its cousin, was brought to the British Isles to interest gardeners in the nineteenth century.
It is also considered highly invasive as it dominates and chokes other wild plant species.