Male Stinging Nettle - Urtica Dioica - With Flowers Shortly Before Blooming Royalty-Free Stock Photo

Known and unpopular are the nettles because of the painful wheals swellings that appear on the skin after touching the stinging hairs. Depending on the species, the consequences vary in severity; for example, the stinging fluid of the lesser stinging nettle Urtica urens is much more painful than that of the greater stinging nettle Urtica dioica. These stinging hairs act as a protective mechanism against predators and are predominantly present on the upper surface of the leaf. They are long, unicellular tubes whose walls are hard and brittle like glass in the upper part due to incorporated silica. The lower, more flexible end is strongly swollen, filled with burning fluid and sunken into a cell cup. The tip consists of a sideways directed little head, under which a kind of predetermined breaking point is present due to the very thin wall here.