Lesser knotweed

(Persicaria campanulata)

Also referred to in some sources as Polygonum campanulatum, Polygonum campanulata or Reynoutria campanulatum, Lesser knotweed is another member of the species that is still actively being sold by garden centres and plant suppliers in both the US and the UK. A native of North India and Southwest China, this knotweed is less invasive than the others but still retains a familiar vigour of growth. Leaf size can be variable, though conforms to the same long shape. Lesser knotweed bears a casual resemblance to Himalayan balsam (Impatiens glandulifera), and its love of moist soil means it is often growing alongside this troublesome plant. Veins on the leaf can sometimes be reddish and the leaves are distinctly grooved in a pattern reminiscent of herring-bone. The undersides of the leaves are much lighter in colour and are felted by small white hairs. Persicaria campanulata grows to a height of around 60-90cm (2-3 feet) and produces flowers mid-summer that remain until the autumn. The flowers are tiny, pale pink or white, and are bell-shaped (hence the name) and produced in clusters on short spikes. Stems are usually clear of foliage for the lower two-thirds of their length and are slightly crooked due to bending at the nodes. The distinctive knotweed ‘zig-zag’ is missing, although leaves are still produced alternate on the stem. This species is less widespread in the UK, though it is more common in parts of Scotland and Northern Ireland.

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