Urtica dioica's stinging hairs in stem, light micrograph. This chemical defense against herbivores is a sharp-pointed trichome reinforced with calcite in the lower half and silica in the upper region. The spherical tip breaks off when hair is disturbed. The sharp tip is left exposed and it penetrates skin surface easily, like a hypodermic needle would. Toxins (histamine, acetylcholine, serotonin, leukotriene, and formic acid) from the bulbous base are injected into the wound causing a painful stinging and burning sensation, a white-red rash and a inflammation. The U. dioica, or stinging nettle, is a green plant of the family Urticaceae, genus Urtica. It is a delicious and nourishing edible herb. Other uses: alternative medicine, pharmacology, neuroscience, fiber, green dye, etc. Field of view size: 5.13 x 7.70 mm (0.202 x 0.303 in)