Urtica urens L.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Species Description - Taprooted annual, simple or branched, 2–5 dm, with numerous stinging hairs; lvs long-petioled, elliptic to broadly ovate and blunt or rounded in outline, deeply incised- serrate, the teeth triangular, acute, upper lvs usually larger than the lower; stipules oblong, 1–3 mm, fl-clusters oblong, often shorter than the petioles; achenes triangular, 1.5–2.5 × 1–1.5 mm; 2n=24, 26, 52. Native of Europe, widely distributed elsewhere as a weed, and occasionally found in our range. May–Sept.