Texas knotweed

Polygonum striatulum var. texense (M. C. Johnston) Costea & Tardif; P. texense M. C. Johnston

Plants perennial, light green, heterophyllous; rhizomes brown, 0.7-3 cm diam. Stems erect to ascending, sparingly branched in distal 1/ 2, not wiry, 25-60 cm. Leaves: ocrea 6-12 mm, proximal part cylindric, distal part soon disintegrating into brown fibers, later leaving almost no fibrous remains; petiole 0-2 mm; blade light green, linear-lanceolate to oblanceolate, 8-35 × 2-8 mm, margins flat, apex acute or obtuse; stem leaves 2.1-4 times as long as adjacent branch leaves; distal leaves sharply reduced, not overtopping flowers (shorter than or equaling flowers). Inflorescences axillary and terminal, spikelike; cymes in distal nodes, 2-6-flowered. Pedicels exserted from ocreae, 2-4 mm. Flowers semi-open; perianth 2-3.5 mm; tube 18-25% of perianth length; tepals overlapping, green with white or sometimes pink margins, petaloid, not keeled, oblong to obovate, cucullate; midveins usually unbranched; stamens 7-8. Achenes enclosed in perianth, brown, ovate, 3-gonous, (1.6-)1.8-2.6(-3) mm, faces subequal or unequal, apex not beaked, edges concave, shiny, smooth or roughened; late-season achenes common, 4-6 mm.

Flowering Dec-Mar or Jun-Oct. Seasonal moist places, sterile prairies, granitic soils; 100-700 m; Tex.

Plants with leaves less-conspicuously veined, flowering August to October, and growing in seasonally moist habitats in central and western Texas are recognized by some authors as Polygonum texense or P. striatulum var. texense (M. Costea and F. J. Tardif 2003).