Persicaria affinis (knot weed)

Native to the region from Afghanistan to Nepal and India and also in China (Tibet) at elevations up to 4,900 m.

A creeping perennial that can form mats several metres across. The leaves are smooth, lanceolate or narrowly elliptic, bluish on the undersides and 3–8 cm long. The flowering stems are 5–25 cm long, with sheathing leaves at the base and dense flower spikes 5.0–7.5 cm long. The flowers are pale pink to red, five lobed and 4–6 mm across. Each flower has eight stamens and three styles. The fruit is a three-angled nutlet.

Hand-coloured lithograph of Persicaria affinis by Ann Barnard (1880) taken from Curtis's Botanical Magazine (Image: RBG Kew)

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Persicaria affinis is cultivated as an ornamental and is widely available from commercial nurseries under this name or the synonym Polygonum affine. Cultivars include P. affinis ‘Superba’ (with red and pale pink flowers) and ‘Donald Lowndes’ (with pale to dark pink flowers). Both have received an Award of Garden Merit from the Royal Horticultural Society. In the Garhwal Himalaya the flowers of knot weed are used as a stimulant, and in the Ladakh region of Jammu and Kashmir an extract of the root is used in traditional medicine against fever.

Knot weed can be seen growing in the Woodland Garden surrounding the Temple of Aeolus, and in the Order Beds at Kew. It can also be found in the Himalayan Glade at Wakehurst; these specimens were brought back and planted by Tony Schilling, who was Curator at Wakehurst between 1967 and 1991.

Search Kew's databases for more information on this species

BBC Plant finder – Persicaria affinis ‘Superba’

Royal Horticultural Society – Persicaria affinis ‘Superba’

Flora of Pakistan, eFloras – Persicaria affinis (listed as Bistorta affinis)

Curtis’s Botanical Magazine (Wiley-Blackwell)