Japanese Knotweed

Japanese Knotweed

Fallopia japonica (Hout. ) R. Decr.
(formerly Polygonum cuspidatum Sieb. & Zucc.)

Polygonaceae (Smartweed Family)

▲ mature plant in partially shaded location

▲ ▼ mature plant along roadside

▲ stems

▲ large colony in flower in Connecticut

▲ flowers

▲ shade-grown young shoot

▲ ▼ young shoots in full sun

▲ ▼ leaves

▲ stem, showing characteristic papery sheath (ochrea) where leaf joins stem

Japanese Knotweed:

a creeping perennial knotweed that reproduces by rhizomes & seeds
has large, heart-shaped leaves and can grow 3-6’ tall, appearing as a shrub
stems large diameter (bamboo-like) and die back to ground each winter
flowers are tiny, whitish-pink in axillary panicles, showy
introduced as an ornamental groundcover, but has escaped cultivation--a newer weed
prefers moist, well-drained, fertile soils--often found on ditchbanks, pastures
prefers full sun but can tolerate moderate shade
appears similar to giant knotweed (Fallopia sachalinensis) with which it can hybridize; but giant knotwed has much larger leaves and grows much larger, as well