Stinging nettle
The European stinging nettle is a botanical camp follower, and has been found around human settlements since at least the Neolithic. Separate male and female stinging nettles have tiny, wind-pollinated flowers crowded into catkin-like inflorescences. Each male flower bud contains four tightly-packed stamens which spring out, releasing pollen when the bud opens. Consequently, minute grains of stinging nettle pollen are commonly found in the air in late summer.
The first formal UK stinging nettle record was in 1562 but since the species is so common it is difficult to determine its detailed distribution before the advent of systematic species recording in the twentieth century. The frequency of stinging nettle in pollen cores implies it is a UK native, although its close association with human activities may indicate it was introduced over at least part of its range. Today there are patches of stinging nettle that mark phosphate-rich debris from long-deserted villages and sites of human occupation more than 1,500 years ago.
Nettles, with their heart-shaped, jagged-margined leaves armed with stinging structures are familiar botanical hazards. The 'stinging points and juice of Nettles' attracted the seventeenth-century, Oxford-educated polymath Robert Hooke, who laid out his observations in Micrographia: or some physiological descriptions of minute bodies made by magnifying glasses (1665), the second publication sponsored by the fledgling Royal Society and an early scientific bestseller. Hooke observed the stinging points comprised two parts; a bristle-like 'syringe-pipe' with a cucumber-like 'little bagg' at the base. He speculated the 'bagg' contained 'corrosive penetrant liquor' which was released when the 'syringe-pipe' was broken.
Micro-anatomical studies show the silica-rich walls of the bristle tip break easily when touched, leaving a hypodermic-like needle through which a biochemical cocktail of histamine, acetylcholine and 5-hydroxtryptamine is released. The result is itching and burning sensations on the skin. Although some people find the sensation pleasant, many resort to the traditional remedy of rubbing the afflicted area with a dock (Rumex species) leaf. However, stinging structures are not unique to nettles; they are found scattered across the plant kingdom and are thought to have evolved as defence mechanisms against herbivores.
The stinging nettle is more than an irritating follower of people. In Les Misérables (1862), Victor Hugo revealed his knowledge of the range of uses to which the stinging nettle could be put; from the production of flax-like cloth and yellow dye, through animal fodder and hay to an early seasonal vegetable.
Further reading
Taylor K 2009. Biological Flora of the British Isles: Urtica dioica L. Journal of Ecology 97, 1436-1458.
Thurston EL, Lersten NR 1969. The morphology and toxicology of plant stinging hairs. Botanical Review 35, 393-412.
Thurston EL 1974. Morphology, fine structure, and ontogeny of the stinging emergence of Urtica dioica. American Journal of Botany 61, 809-817.
Stephen Harris