Japanese Knotweed

[Polygonum cuspidatum Sieb. & Zucc.]

Polygonaceae (Smartweed Family)

▲ mature plant in partially shaded location

▲ ▼ mature plant along roadside

▲ stems

▲  flowers

▲ shade-grown young shoot

▲ ▼ young shoots in full sun

Japanese Knotweed:  (not in Weeds of the Great Plains; pp. 278-279, Weeds of the Northeast)

·        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