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
