Polygonum cuspidatum  (Fallopia japonica, Reynoutria j.) Japanese knotweed Polygonaceae POCU*p; Bx, bg, br, bz, cf, ht, pb, rd, sf, sn, up, vc, wv (Yost et al. 1991); NY, ct, hb, iw, n, wr; Q, a, cu, dp, f, fr, i, j, lk, rb, rw, tl, u, wl; K, do, fs, vb; R, ah, ar, bd, bg, bk, bm, c, ca, cb, cg, cl, cs, d, ev, fk, gr, h, is, js, jl, k, lc, lp, lt, mc, mm, ok, pm, pr, r, se, sm, sp, t, v, w, wp, wt, x;


Polygonum cuspidatum.commons.wikipedia.org

Polygonum cuspidatum.commons.wikimedia.org. (Accessed 4/2014).

Polygonum cuspidatum is a large Perennial herb, to 3 m tall; extensively colonial from rhizomes, also forming large root-crowns; stems stout, , cylindrical, internodes hollow, nodes prominent, bamboo-like. 

Leaves alternate broadly egg-shaped, tip pointed, base truncate to very shallowly lobed with small angles, to 15 cm long, 10 cm wide. 

Flowers white, 5-parted (tepals), radially symmetrical, very small, in dense racemes; plants dioecious, pollinated by bees, ants, butterflies and beetles (Niewinski et al. 1999); blooming and fruiting July-Sept. (Hough 1983). 

Polygonum cuspidatum© Les Mehrhoff, 2008-2010 · 2.Discoverlife.org

Polygonum cuspidatum© Les Mehrhoff, 2008-2010 · 2.Discoverlife.org (Accessed 2/2017).

Fruit dry, achenes 0.3 cm, 3-sided, winged by old tepals, collectively showy; dispersed by wind or water through fall and winter. Seeds may be eaten by birds (Niewinski et al. 1999). 

Wetland status: FACU- (but often found in wet soil). 

Frequency in NYC: Very common (ubiquitous). 

Origin: Japan. 

Polygonum cuspidatum.commons.wikimedia.org. (Accessed 4/2014).

Polygonum cuspidatum.commons.wikimedia.org. (Accessed 4/2014).

Habitat: Open areas, on fill, disturbed sites, second growth, floodplains, roadsides, wetland edges. Wet to dry soil. Appears to tolerate flooding well. Appears intolerant of low nutrient, acid soil. Found in soils pH 5.7-7.8 (Gargiullo, Kruzansky and Larson unpublished data). Listed as intolerant of shade but observed invading shady edges and understories of swamp forests (Seiger 1995). 

Notes: Originally cultivated as an ornamental. Evidence from Britain indicated that all reproduction was vegetative from rhizome fragments (Seiger 1995). However, recent studies in the eastern U.S. show that seed is not only viable (germination about 90%), but that seedlings may flower and reproduce in their first year of growth. Viable seed was also recovered from soil cores (Niewinski et al. 1999). An aggressive, very invasive, weedy, plant along waterways and disturbed sites. Listed as one of the “top twenty” invasive alien plants by the NYS Natural Heritage Program’s Ad hoc committee on invasive plants (see also: P. sachalinense). Fallopia x bohemica is a hybrid of Polygonum cuspidatum and P. sachalinense with characteristics intermediate between the two parents (Niewinski et al. 1999).