Utah knotweed

Polygonum douglasii Greene var. utahense (Brenckle & Cottam) S. L. Welsh

Herbs. Stems erect, green, simple or with few branches, not wiry, 1.5-3.5 cm, papillose-scabridulous. Leaves uniformly distributed, articulated to ocreae, basal leaves persistent, distal leaves abruptly reduced to bracts; ocrea 2-3.5 mm, papillose-scabridulous, proximal part funnelform, distal part hyaline, lacerate; petiole absent; blade 1-veined, not pleated, linear-subulate, 6-14 × 1 mm, coriaceous, margins revolute, touching along midrib, apex acute, mucronate, papillose. Inflorescences axillary and terminal, spikelike, dense; cymes overlapping, starting almost from stem base, 2-4-flowered. Pedicels enclosed in ocreae, erect to spreading, 0.4-1 mm. Flowers open; perianth 2-2.5 mm; tube 20-25% of perianth length; tepals overlapping, uniformly white, petaloid, oblong to widely obovate, cucullate, navicular in distal 1/4, apex rounded; midveins branched; stamens 8. Achenes enclosed in perianth, black, elliptic, 1.5-2 mm, faces subequal, shiny, smooth.

Flowering Jul-Sep. Dry, sandy ravines, rocky Navajo sandstone spur; 2300 m; Utah.

Polygonum utahense has been treated as a synonym of P. sawatchense by some authors (e.g., S. L. Welsh et al. 1987; J. T. Kartesz and C. A. Meacham 1999). Its perianth morphology suggests a relationship with P. cascadense, from which it differs in its dwarf habit and uniformly papillose leaves with margins revolute, touching along midribs.