Stinging nettle

The stinging nettle (Urtica dioica) is a herbaceous flowering plant native to Europe, Asia, northern Africa, and North America, and is the best known member of the nettle genus Urtica.

The taxonomy of stinging nettles in the genus Urtica has been confused, and older sources are likely to use a variety of systematic names for these plants. Formerly, more species were recognised than are now accepted. However, there are at least five clear subspecies, some formerly classified as separate species:

Other species names formerly accepted as distinct by some authors but now regarded as synonyms of U. dioica include U. breweri, U. californica, U. cardiophylla, U. lyalli, U. major, U. procera, U. serra, U. strigosissima, U. trachycarpa, and U. viridis. Other vernacular names include tall nettle, slender nettle, California nettle, jaggy nettle, burning weed, and bull nettle (a name shared by Cnidoscolus texanus and Solanum carolinense).

Stinging nettles are a herbaceous perennial, growing to 1-2 m tall in the summer and dying down to the ground in winter. It has very distinctively yellow, widely spreading roots. The soft green leaves are 3-15 cm long, with a strongly serrated margin, a cordate base and an acuminate tip. Both the leaves and the stems are covered with brittle, hollow, silky hairs that were formerly thought to contain formic acid as a defence against grazing animals. Recent research has revealed the cause of the sting to be from three chemicals – a histamine that irritates the skin, acetylcholine which causes a burning sensation and serotonin, that encourages the other two chemicals. Bare skin brushing up against a stinging nettle plant tends to break the delicate defensive hairs and release the trio of chemicals, usually resulting in a temporary and painful skin rash similar to poison ivy, though the nettle's rash and duration are much weaker.

Stinging nettles are abundant in northern Europe and much of Asia, usually found in the countryside. It is less gregarious in southern Europe and north Africa, where it is restricted by its need for moist soil. In North America it is widely distributed in Canada and the United States, where it is found in every province and state except for Hawaii and also can be found in northernmost Mexico. In North America the stinging nettle is far less common than in northern Europe. The European subspecies has been introduced into North America as well as South America.

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 to the ground during the Highland Clearances can still be identified.