Urtica species grow as annuals or perennial herbaceous plants, rarely shrubs. They can reach, depending on the type, location and nutrient status, a height of 10–300 centimetres (3.9–118.1 in). The perennial species have underground rhizomes. The green parts have stinging hairs. Their often quadrangular stems are unbranched or branched, erect, ascending or spreading.
Most leaves and stalks are arranged across opposite sides of the stem. The leaf blades are elliptic, lanceolate, ovate or circular. The leaf blades usually have three to five, rarely up to seven veins. The leaf margin is usually serrate to more or less coarsely toothed. The often-lasting bracts are free or fused to each other. The cystoliths are extended to more or less rounded.