Properties and uses
Originally from Peru (where wild potatoes still grow, with flesh of yellow, red, purple or black) this starchy, tuberous perennial is a member of the nightshade family. Its stalks, leaves and berries can all be toxic, as can tubers that have turned green. With over 1000 varieties potatoes are now a worldwide staple and the world's fourth largest food crop; but the price for growing them so far from home is their susceptibility to frost and disease, especially blight, a fungal infection fostered by damp climates.

Varieties are classified as early, second early and maincrop. Maincrop, the heaviest cropping, are intended for winter storage, while earlies, being lighter cropping and thin-skinned are grown to fill the gap between the running out of old potatoes and maturing of second earlies. Different kinds of flesh (waxy, floury, etc.) have been cultivated for use in salads, for chips, boiling and roasting.

Potatoes have a high carbohydrate content, in the form of starch, some of which is not digested and so has benefits as fibre. They contain proteins, vitamin C and minerals, especially potassium. As these nutrients are evenly divided between skin and flesh, potatoes baked or steamed in their skins have significantly more nutritional value.
"No potatoes! No popery!" was the election slogan of a parliamentary candidate for Lewes in 1765.  First domesticated in  the Andes 7000 - 10,000 years earlier, valued by Peruvian Incas as a winter storage crop, brought to Europe by the Spanish in the 16th century, the potato had been regarded by Europeans first as a novelty, then as animal food, and then, by northern protestants, with deep mistrust on the grounds that no mention of it is made in the Bible. Catholic communities adopting a more tolerant attitude, potato-eating came to be seen in England as a papist habit.
It took a widespread failure of grain crops in the late 18th century, and resulting famines in Germany, Ireland and Scotland for the importance of potatoes as a food crop to be recognised in northern Europe.  Their advantages over more traditional crops then became clear: they are one of the few plants people can live on with no other food, they produce high yields from little land, and require minimal preparation (no threshing or grinding). In Britain the popularity of "the lazy root" spread rapidly: Gilbert White wrote in 1778 that potatoes "are now much esteemed by the poor who would scarce have ventured to taste them in the last reign". 
By the 19th century they had become a staple food, a factor in  Europe's population boom. Blight, unknown when potatoes first arrived in Europe, now became a grave hazard.
In the 1840s blight became epidemic in Ireland, where a system of landless labourers renting tiny plots of land had resulted in a population entirely dependent on potatoes. A series of famines caused over a million deaths and massive migration. No cure was known until potato-growers downwind from a copper-smelting plant in South Wales noticed that their crops were blight-free.  Since then 'Bordeaux mixture' (a spray of copper sulphate and lime) has been used to protect conventionally grown crops.  In Organic production limited use of Bordeaux mixture is allowed, but the grower has to apply for permission to use it, siting the reasons.  Most organic growers chose blight resistant varieties so as to avoid the problem in the first place!
In the 20th century potatoes spread further over the globe, the most rapid growth in recent decades being in east Asia, with China now the world's greatest producer.