Annual nettle (Burning nettle, small nettle, dwarf nettle, lesser nettle, stinging nettle)
Urtica urens

10–50 cm (4–20 in.). Stem ascending–erect, often branching, 4-edged, with stinging hairs. Staminate and pistillate flowers separate, but on the same plant, flowers very small. Staminate flower: tepals 4, with sepals, hairy, translucent. Stamens 4, filaments curled inwards as buds. Pistillate flower: tepals 4, with sepals, in different-sized pairs, hairy, larger tepals usually with one stinging hair each. A single carpel, stigma brush-like. Inflorescence catkin-like, 1–2 cm (0.4–0.8 in.) long, shorter than leaf-stalks. Opposite, stalked, stipulate. Blade elliptic–quite round, with wedge-shaped–blunt base, short-tipped, deeply serrated, both sides with few stinging hairs, light green. Blade approx. 1.5 times as long as broad, stalk approx. 2/3 length of blade.