Japanese knotweed, giant hogweed and Himalayan balsam are three of the most common invasive non-native plants in Northern Ireland. Identification: Himalayan knotweed is a perennial, herbaceous plant with a woody root. Control of knotweed is challenging and often requires a watershed approach to be effective along waterways. The growing patterns, leaf structures, interior stem, and pink flowers set this plant apart. Knotweed is a highly invasive perennial weed which can cause severe damage to both residential and commercial property. It can cause declines in native plants, including rare or localised species, due to their quick growth and shading out other plants. Himalayan knotweed leaves are narrow (its width is less than half its length), distinguishing it from giant, Japanese and Bohemian knotweeds, which have leaf widths more than 2/3 their length. Knotweed Himalayan Knotweed Identification Flowers: All knotweed species, with the exception of Himalayan knotweed, have small, white/ green flowers that grow in showy, plumelike, branched clusters along the stem and leaf axils (joints). Himalayan Knotweed Persicaria wallichii This plant is in a different family from the three knotweeds above, and looks more elegant than them. New shoots start to arise during the early spring. They are very fast growers and can reach full height by the end of June. It’s a large, thicket-forming plant, reaching up to 2m tall, and has become established on stream sides, hedge banks, woodland edges, roadsides, railway banks and waste ground. Japanese knotweed. Himalayan Balsam identification. Canes are hollow and have jointed nodes. Himalayan knotweed flowers are usually pinkish/white. Himalayan knotweed is highly invasive as it spreads vegetatively, grows quickly, shading out native species, and is a habitat generalist. Polygonum wallichii Himalayan knotweed is very distinct. Stems are 2-3 m tall and are branched in the upper half. Like other knotweed species, it is difficult and expensive to control. It forms dense clumps which can be up to three metres in height. County-led knotweed control projects. I only include it because it does sometimes get confused with these other species. Reynoutria x bohemica) These are giant knotweed (Fallopia sachalinensis), Japanese knotweed (F. japonica) and Bohemian knotweed (F. x bohemica). Himalayan Balsam is a distinctive plant with reddish jointed stems and long, green, oval-shaped leaves. Himalayan knotweed (Persicaria wallichii) The most distinctive of these species, it tends to be shorter, denser and more clump-forming and has pinker flowers and stems that are not hollow. This plant is similar to Japanese knotweed, but has longer, pointed leaves. The flowers range from fuchsia to pale pink in colour and tend to appear between June and October, followed by seed pods … The leaf base of giant knotweed is deeply heart shaped compared to the base of Japanese knotweed, which forms a right angle with the leaf stem. Appearance. Bohemian knotweed (Fallopia Bohemica syn. Bohemian knotweed Giant knotweed Dwarf knotweed Himalayan knotweed. Unlike the other species, the Himalayan knotweed grows close to the ground, aiding in its dense nature. Knotweed Family Identification. Himalayan Knotweed. A non-native invasive plant. Koenigia polystachya is a species of flowering plant in the knotweed family, known by the common names Himalayan knotweed and cultivated knotweed.It has several regularly used synonyms, including Polygonum polystachyum, Aconogonon polystachyum and Persicaria wallichii.. 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