Engelmann's knotweed

Polygonum douglasii Greene subsp. engelmannii (Greene) Kartesz & Gandhi

Herbs. Stems erect, green or purplish brown, branched from base, not wiry, 4-30 cm, glabrous or minutely papillose-scabridulous. Leaves uniformly distributed, articulated to ocreae, basal leaves persistent, distal leaves abruptly reduced to bracts; ocrea 3-5 mm, papillose-scabridulous or glabrous, proximal part funnelform, distal part becoming lacerate with age; petiole 0.1-2 mm; blade 1-veined, not pleated, linear-oblanceolate, 10-20(-25) × 1-3(-4) mm, margins revolute, smooth, apex acute to mucronate. Inflorescences axillary and terminal, spikelike, loosely floriferous nearly to base, elongate; cymes spaced along branches, (1-)2-4-flowered. Pedicels exserted from ocreae, reflexed, 1-3 mm. Flowers closed; perianth 1.5-2(-2.5) mm; tube 18-26% of perianth length; tepals initially overlapping and cucullate, later forced apart by developing achene, greenish or sometimes purple, with white margins, petaloid or sepaloid, oblong, ± flat or navicular, apex rounded; midveins unbranched; stamens 5-8. Achenes exserted from perianth, black, elliptic, 1.2-2.3 mm, faces subequal, shiny, smooth.

Flowering Jun-Sep. Dry to moist sandy or well-drained soils, sagebrush desert to lower mountains; 1000-1500 m; Alta., B.C.; Colo., Idaho, Mont., Nev., S.Dak., Utah, Wyo.