Persicaria affinis in autumn colours.

Two of my favourite herbaceous plants of late summer and early autumn are both in the genus Persicaria: Persicaria affinis and Persicaria amplexicaule. In English these plants are bistorts or knotgrasses, members of the Dock Family, Polygonaceae.

Persicaria affinis is a semi-evergreen perennial that spreads to form a wide mat. The leaves are dark green and elliptical and erect spikes of small white, pink or red flowers are borne above these from July to October, reaching between 20 and 30 cm high. In autumn the leaves turn red or pink. Provided the soil isn’t too dry Persicaria affinis can be grown on a sunny bank and will trail over the edge.

Good varieties of Persicaria affinis include ‘Superba’ (rose pink flowers), ‘Donald Lowndes’ (pink flowers) and ‘Darjeeling Red’ (red-pink flowers). We have the latter two in the garden at The Belvedere Centre and ‘Darjeeling Red’ at Grapes Hill Community Garden, where it is making an escape bid beyond the garden railings and softening the edge of the adjacent car park.

Persicaria amplexicaule is a much more robust plant, growing to 1.2 metres tall with large, prominently veined ovate leaves and small flowers borne in dense, long-stalked spikes which are up to 10cm long. It looks more like a dock than P. affine. It is happy in sun or part shade in reasonably moist soil.

Persicaria amplexicaule ‘Rosea’

Varieties include ‘Rosea’ (pink flowers), ‘Firetail’ (white – pink flowers) and ‘Inverleith’ (deep pink flowers, much lower growing – to about 50cm tall). In the Belvedere Centre Garden ‘Rosea’ has been in flower since late August and its flower spikes have proved very attractive to honeybees.

The Beth Chatto Garden website lists several varieties of Persicaria. Other species suitable for the garden include the spreading Persicaria microcephala ‘Red Dragon’, whose leaves are lance-shaped and purplish-green. The leaf centres are purple or bronze and there is silvery v marking around the edge of the leaf. P. microcephala “Red Dragon” has round clusters of tiny white flowers in late summer and autumn.

The annual garden weed known as Redshank or Persicaria is also in the genus – it is Persicaria maculosa. The name Redshank comes from its sprawling red-jointed stems. It has spikes of small pink flowers and grows on disturbed ground and is widely distributed in Britain (see map). It is edible in small quantities (see the Plants For A Future website for more data).

When I was learning plant names Persicaria maculosa was known as Polygonum persicaria. This was part of a bigger reclassification, as the genus Persicaria has been split from the genus Polygonum in recent years, leading to a number of name changes.

Update August 2014: I have since added a third Persicaria to my list of favourites, Persicaria polymorpha or White Fleeceflower.