Polygonum sachalinense  (Reynoutria s.) giant knotweed Polygonaceae POSA2*p; Bx, br; R, bg, d;

 

Polygonum sachalinense.Les Mehrhoff.www.discoverlife.org

Polygonum sachalinense.Les Mehrhoff.www.discoverlife.org (Accessed 4/2014).

Polygonum sachalinense is a perennial herb to 4 m tall extensively clonal from rhizomes, also forming large root-crowns; stems stout, angular, nodes bamboo-like. 

Leaves alternate, heart-shaped, round-lobed at base to 40 cm long, 22 cm wide. Distinguished from P. cuspidatum by leaf shape, that of P. cuspidatum is broadly egg-shaped, base truncate to very shallowly lobed with small angles.

Flowers very small, in racemes, plants dioecious, pollinated by bees, ants, butterflies and beetles (Niewinski et al. 1999), blooming and fruiting July- Sept. 

Fruit dry, winged, dispersed by wind or water through fall & winter, achenes 0.4 cm, 3-sided. Seeds may be eaten by birds. 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, 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). 

Wetland status: UPL but often found on floodplains and in wet soil. 

Frequency in NYC: Apparently very infrequent, but very similar to P. cuspidatum and probably not distinguished from it in most collections. 

Origin: East Asia.

Habitat: Disturbed sites.  

Notes: Invasive. Slugs eat seedling cotyledons (Niewinski et al. 1999). See also Pcuspidatum