Persicaria affinis (knot weed)
This mat-forming perennial with smooth leaves and spikes of small pink or red flowers was once admired in the Himalaya by Sir Joseph Hooker, one of Kew’s early directors.
About this species
This perennial forms mats that creep over rocks and steep slopes in the central Himalaya. The fresh green leaves emerge in spring and the flower spikes develop in late summer, bearing numerous, small pink or red flowers. After the first frosts, the leaves turn red then chestnut-brown.
One of Kew’s early directors, Sir Joseph Hooker, admired this species in the Himalaya, and described it ‘hanging in rosy clumps from moist precipices’.
Geography & Distribution
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.
Illustration from Curtis's Botanical Magazine
Hand-coloured lithograph of Persicaria affinis by Ann Barnard (1880) taken from Curtis's Botanical Magazine (Image: RBG Kew)
Curtis’s Botanical Magazine (Editor: Martyn Rix) provides an international forum of particular interest to botanists and horticulturists, plant ecologists and those with a special interest in botanical illustration.
Now well over two hundred years old, the Magazine is the longest running botanical periodical featuring colour illustrations of plants. Each four-part volume contains 24 plant portraits reproduced from watercolour originals by leading international botanical artists. Detailed but accessible articles combine horticultural and botanical information, history, conservation and economic uses of the plants described.
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- Traditional medicine
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.
This species at Kew
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.
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