Herbs, perennial, sometimes suffrutescent, 7-12(-25) dm; roots not also arising from proximal nodes; rhizomes present. Stems ribbed, glabrous or densely pubescent. Leaves: ocrea reddish brown, cylindric, 10-40 mm, base inflated, surface glabrous or densely pubescent; petiole 0.3-2(-3) cm, glabrous or densely pubescent; blade (7.5-)9-22(-27) × 2.8-7.8 cm, base cordate to truncate, margins ciliate, apex acuminate to caudate-acuminate, faces pubescent abaxially, glabrous or pubescent adaxially. Inflorescences 40-110 × 10-55 mm; peduncle 10-80 mm, glabrous or pubescent; ocreolae not overlapping, margins eciliate. Pedicels ascending to spreading, 1-4 mm, glabrous. Flowers 3-9 per ocreate fascicle; perianth white or pinkish, often with scattered reddish glands, glabrous, nonaccrescent; tepals oblong to obovate, dimorphic, outer 3 larger than inner 2, 2.2-3.8 mm, margins entire, apex obtuse to rounded; filaments inserted at bases of tepals, distinct, glabrous; anthers red to purple, ovate; styles distinct. Achenes included, brown, 3-gonous, 2.1-2.5 × 1.3-1.8 mm, dull, minutely roughened. 2n = 22.

Flowering Aug-Oct. Moist disturbed places, marshes; 0-500 m; introduced; St. Pierre and Miquelon; B.C.; Calif., Mass., Oreg.; Asia (Bhutan, China, India, Nepal, Tibet).

A Himalayan sp. that is reported to spread occasionally from cult. in the ne. part of our range. It would key to P. densiflorum, from which it differs in its showy, open-paniculate infls, often wider lvs (to 8 cm wide) that tend to be narrowly truncate or cordate-auriculate at base, and in other respects. It is more nearly related to nos. 37 [Polygonum cuspidatum Siebold & Zucc.] and 38 [Polygonum sachalinense F. W. Schmidt], but the tepals are not keeled or winged and are scarcely accrescent.

Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.

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