Slender or pleat-leaf knotweed

Polygonum tenue var. protrusum Fernald

Herbs. Stems erect, green or brown-ish, simple or branched from below middle, not wiry, 5-50 cm, glabrous or papillose-scabridulous. Leaves uniformly distributed, articulated to ocreae, basal leaves caducous or persis-tent, distal leaves abruptly reduced to bracts; ocrea 6-15 mm, glabrous or papillose-scabridulous, proximal part cylindric, distal part soon disintegrating into a few brown fibers; petiole 0.1-1 mm; blade 1-veined, with 1 pleat on each side of midrib, narrowly lanceolate to linear, 25-40 × 1-8 mm, margins usually flat, papillose-denticulate, apex mucronate or cuspidate. Inflorescences axillary and terminal, spikelike, slender, elongate; cymes spaced along branches, 1-2(-3)-flowered. Pedicels enclosed in ocreae, erect, 1-1.5 mm. Flowers closed; perianth 2.5-4.2 mm; tube 15-22% of perianth length; tepals overlapping, green, often brownish when dried, with pink or white margins, petaloid or sepaloid, elliptic, cucullate, navicular, apex rounded; midveins usually unbranched, rarely branched; stamens 8. Achenes enclosed in or slightly exserted from perianth, black, elliptic to oblong, 2.3-4 mm, faces subequal, shiny, smooth or minutely striate-tubercled near edges and apex. 2n = 20.

Flowering Jun-Oct. Dry acid soils in exposed sites; 100-1000 m; Ont.; Ala., Ark., Conn., Del., D.C., Ga., Ill., Ind., Iowa, Kans., Ky., La., Maine, Md., Mass., Mich., Minn., Mo., Nebr., N.H., N.J., N.Y., N.C., Ohio, Okla., Pa., R.I., S.Dak., Tenn., Tex., Vt., Va., W.Va., Wis., Wyo.