Stinging nettles are also referred to as common nettles. This perennial is a flowering weed. Its small, translucent spines deliver formic acid when broken, creating a stinging sensation. When harvested and cooked, this plant can be very nutritional. However, the plant can also cause a person to go into anaphylactic shock and die. These plants also have finger-like roots which allow it to spread very quickly. Use extreme care when removing this plant from your garden.