Fallopia japonica var. compacta; a variable species of which former names have included: Polygonum pictum, Polygonum compactum and Polygonum reynoutria.
Dwarf Japanese Knotweed is a hardy, herbaceous, rhizomatous perennial. Plants are mainly dioecious and functionally female (male-sterile): though some are monoecious, with both male-fertile and functionally female (male-sterile) flowers. Stems grow to 1 metre, reddish. Leaves are proportionally smaller, dark green suborbicular, bases truncate, margins crimped. Flowers reside in dense upright panicles, growing to 6cm long, and are often pink in male-sterile individuals. The fruits are similar to other Knotweeds.
Plants known as Fallopia japonica var. compacta are alpine variants of Fallopia japonica, introduced to the UK for garden use. Populations are of variable height, and with the amounts of red pigmentation on stems, flowers and seed heads, likewise varying. Though invasive in a garden context, it has not gained important pest status.
Fallopia japonica var. compacta can also hybridise with Fallopia sachalinensis to produce a strain of Fallopia x bohemica. back to top