lesser knotweed

P. affinis is a mat-forming herbaceous perennial about 25cm high with elliptic to lance-shaped dark green leaves, 5-15cm long, which turn red-bronze in autumn, and from midsummer to mid-autumn spikes 5-8cm long of flowers, each 5mm long, which open bright reddish pink, fade to pale pink, and then turn brown during winter; it is an excellent ground-cover plant