The stinging nettle is an inevitable part of the British
countryside, and is also found around the world,
living in wooded areas and disturbed ground¹. The stinging nettle has the
Latin name Urtica Diotica, and is part of the
nettle family (Urticaceae) of the genus
Urtica. It is a perennial which flowers
between June and September; the flowers are arranged in long
catkins and are coloured green, red or white.
These include separate "male" and "female" flowers.

The nettle has toothed leaves, which
are a couple of inches wide and appear in pairs from the
stem on short stalks. The main stem is suqare-ish, and the plant is typically 2-4 feet high (that's about 1 meter). These leaves are covered in tiny
hairs, which, when brushed past give Urticaria, or
A-nasty-red-rash-which-itches-like-hell, for a while.
Some nettle stings are more severe,
Urtica urentissima, for example, is found in Java, and can cause a rash for a whole year
and may in extreme cases cause death.

If you do brush past and get stung, it is vitally
important not to scratch the rash. The best thing to do
is to apply a soothing lotion to it, and have a nice,
hot cup of tea. If you have no soothing lotions on you,
try washing the sting out, or use
a natural remedy - the leaves from the dock plant², or (amazingly) the juice from the nettle.

Dead nettles of the genus Laminum come in White, Purple & Yellow varieties, but
do not sting. They are protected from harm from looking like the Stinging Nettle.

By far the best advice about cooking with stinging nettles comes from Identifying and Harvesting Edible and Medicinal Plants in Wild (and Not So Wild) Places, which says

Clean and chop nettles wearing rubber gloves. Once you’ve cooked them a little, the stingers are deactivated, and the plant becomes wonderfully edible.

Uses for Nettles

Nettles have more use than you might normally expect....

• 
  The University of Plymouth has proved that the Stinging Nettle can have a beneficial effect on arthritis sufferers (osteoarthritas), confirming folk law dating back to Roman times,
  which suggested flogging with Nettles (Urtication) as a cure for chronic rheumatism.
  
• 
  Nettle products include soup, tea, nettle pudding, porridge, beer, Yarg Cheese which is wrapped in Nettles, paper, cloth dye (which is yellow, and comes from the root).
  
• 
  Nettles provide a source of food for caterpillars, some of which feed exclusively on the Nettle. It is also a food source for a wide variety of insects, including Ladybirds, and, according to hdra.org.uk, supports 107 species.
  
  
  Carol Chittock of the Diss Hedgehog Advisory Centre
  suggests you "leave a small area natural so that the wild grass grows, stinging nettles as well, because butterflies like stinging nettles to lay their eggs on, the eggs then turn in to caterpillars, and hedgehogs love caterpillars."
  
• 
  Nettles act as an accelerator for compost, and a rich source of nitrogen and minerals. Plus it's a source of vitamin A and C.
  
• 
  Nettles are alleged to be anti-inflammatory (and generally helpful with all skin conditions), antiparasitic, antiseptic, a digestive stimulant, and a menstrual promoter.
  It may cure rheumatism, arthritis muscle wastage problems, inflammation and, bizarrely, head lice.
  If it fails to remove the lice, it could still stimulate hair growth.
  The nettle has been used medicinally by the Greeks and later the Romans.
  In fact, it has been alleged to cure almost everything.
  
• 
  Also, it doesn't shed enough pollen to be a major cause of hay fever.
  

Getting rid of Nettles

Because the nettle has extensive food reserves in its roots, you will need to cut them back repeatedly for many years.
Estimates vary between cutting them back 3-4 times a year in 2 years, to 3 times a year for 3 years (from the Royal Horticultural Society).