Potty Gardening Club: Plants that Fight Back
Plants are not always the defenceless things you may think they are. Some fight back! Roses, brambles and hawthorn have thorns and holly has prickles. Thorns, spines, and prickles are hard modifications of leaves, stems or buds with sharp ends whose sole purpose is to deter animals from eating them. Nettles are different and perhaps the masters of self-defence with a special adaptation like something out of a science fiction story.
Nettle stinging hairs are made from glass! Its true – the tips of the nettles stinging hairs are made of glass! But not transparent glass, like your windows, but a special silica glass. Its not really known how plants make this glass, but plants like nettles suck in silica, which is in the soil, through their roots and then somehow convert it into little fibres of glass that make the hairs. The glass made by plants is called “phytoliths”.
Stinging nettles are covered with hundreds of tiny hollow hairs called trichomes. Can you see the glass needle hairs in my picture?
When something brushes the hairs, the fragile silica tips break off and the hair becomes needle-like, piercing the skin and injecting the sting-causing chemicals. You can see this in my close-up photo of a triggered hair. If you have ever put your hand on a nettle in your garden or brushed against any you will know how painful this can be. Ouch!
Nettles are perennial plants, growing in the summer and dying down to the ground in winter, waiting to reappear the following spring.
Nettles have a spreading rootstock (rhizome) and root runners (stolons) just below the soil surface. They also produce abundant seed to increase the chance of spreading.
Nettles do well in areas of human habitation and abandoned buildings where human and animal waste may increase the soil fertility. They are also found in meadows as an undergrowth plant alongside hedges and in wetter environments.
Nettles are an important food plant for several species of butterfly larvae, such as the peacock butterfly, the comma and the small tortoiseshell. It is also eaten by the larvae of some moths, but though nutritious it is generally avoided by most other things because of its sting. But cooking the plant destroys the stinging hairs, making the nettle safe to eat. In the past, nettle shoots and leaves were used as a Spring vegetable and is still used as a popular herbal tea today, it is high in vitamin A and C as well as iron.
Would you believe that nettles have been used to make clothing? Nettle textiles have been found in Denmark Iron Age burial sites 3000 years old. During World War I, due to a shortage of cotton, German army uniforms were made from nettle fibres. More recently some clothing companies have started to produce nettle textiles for clothing again. I wonder if it’s itchy!
Written by Rob Gagliano, Casual Learning Development Leader and Natural Science Collections Volunteer