Stinging nettle or common nettle (Urtica dioica) is a herbaceous perennial flowering plant, native to Europe, Asia, northern Africa, and North America.
Stinging nettle can grow to 1 to 2 m (3 to 7 ft) tall in the summer and dying down to the ground in winter. It has widely spreading rhizomes and stolons, which are bright yellow as are the roots. The soft light green leaves are 3 to 15 cm (1 to 6 in) long and are borne oppositely on an erect wiry green stem. They may be confused with dead-nettles.
The leaves have a strongly serrated margin (Dentate), a Cordate base and an acuminate tip with a terminal leaf tooth longer than adjacent laterals. It bears small greenish or brownish 4-merous flowers in dense axillary inflorescences. The underside of leaves and stems are very hairy with non-stinging hairs. The topside of the leaves bear the many stinging hairs (trichomes), whose tips come off when touched, transforming the hair into a needle that will inject several chemicals: acetylcholine, histamine, 5-HT or serotonin, and possibly formic acid. This mixture of chemical compounds cause a sting or paresthesia from which the species derives its common name.
In the UK stinging nettles have a strong association with human habitation and buildings. The presence of nettles may indicate that a building has been long abandoned. Human and animal waste may be responsible for elevated levels of phosphate and nitrogen in the soil, providing an ideal environment for stinging nettles. This seems particularly evident in Scotland where the sites of crofts razed during the Highland Clearances can still be identified.
Nettles are the exclusive larval food plant for several species of butterfly, such as the Peacock Butterfly or the Small Tortoiseshell, and are also eaten by the larvae of some moths. Ladybirds often hunt aphids on Stinging Nettles and although many people think that they are a pest, they are quite important for the British Springtime ecosystem.