There is general agreement among contemporary botanists that the potato originated in the Andes, all the way from Colombia to northern Argentina, but with a concentration of genetic diversity, both in the form of cultivated and wild species, in the area of modern day Peru. The potatoes cultivated in the Andes are not all the same species. The major species is Solanum tuberosum ssp. andigena (a tetraploid with 48 chromosomes,) then there are four diploid species (with 24 chromosomes) by the names of Solanum stenotomum, Solanum phureja, Solanum goniocalyx and Solanum ajanhuiri. There are two triploid species (with 36 chromosomes) Solanum chaucha and Solanum juzepczukii, and finally, there is one pentaploid cultivated species (with 60 chromosomes) called Solanum curtilobum.
Andean potatoes are adapted to short day conditions and Chilean potatoes to long day conditions. There is sufficient evidence that the tetraploid Andean short day potato was the one that first arrived in Southern Spain in about 1565. From there it spread to the rest of Europe, adapting to European long day conditions in a period of about two hundred years. In order to botanically distinguish potatoes adapted to short days from those thriving and producing tubers under long day conditions, Solanum tuberosum has been split into two subspecies by present-day taxonomists, Solanum tuberosum ssp. tuberosum (adapted to long days) and Solanum tuberosum ssp. andigena (adapted to short days.) Apart from their different photoperiodic reaction, these two subspecies are also distinct morphologically, though the differences are apparent only to an experienced taxonomist. Russian taxonomists did, in fact, create two different species in the early part of the 20th century, Solanum tuberosum and Solanum andigenum, to mark the same distinction. The process of adaptation to long days has happened once before as the potato moved from the Andes to the south of the continent. This was before the Europeans arrived in South America. Chile still has a large amount of valuable potato germplasm adapted to long days.
Historical and genetic evidence suggests that the potato reached India not very much later than Europe, probably taken there by the Portuguese. In isolated areas in the Himalayas of India and Nepal, so called “desi” potatoes are still grown, and they are very similar to the short day adapted modern Andean potato, Solanum tuberosum ssp. andigena.
There are about five thousand potato varieties worldwide. Three thousand of them are found in the Andes alone, mainly in Peru, Bolivia, Ecuador and Colombia. They belong to eight or nine species, depending on the taxonomic school. Apart from the five thousand cultivated varieties, there are about 200 wild species, many of which can be cross-bred with cultivated species, which has been done repeatedly to transfer resistances to certain pests and diseases from the gene pool of wild species to the gene pool of cultivated potato species. The list of varieties found in European, North American or Asian markets is very limited, and these varieties are all of the same species, Solanum tuberosum ssp. tuberosum.
These potatoes are often referred to as “Irish” potatoes in the English speaking world because of their association with the Great Irish Famine, which began in 1845 and lasted for six years. The Irish peasant population had become highly dependent on the potato because of the relatively large amount of food that could be produced on fairly small holdings. Immigrant farmers from the Palatinate region of Germany brought their own crops, such as turnips, to Western Ireland. They were much less dependent on the potato than their native Irish neighbors and were largely spared the effects of the potato famine. The disease killing the Irish potato crop was the late blight fungus Phytophthora infestans. The long lasting aftereffects of this famine are well known and well documented.
What is less well known is the role of the British during the potato famine. Rich aristocratic British landowners continued to export grain from Ireland to other parts of the world even as tens of thousands of Irish were dying of starvation. However, there were some British owned estates where not one Irish peasant starved during the famine. Authors like Salaman have written in detail about that situation, which has also been recognized by contemporary British historians.
Most modern potatoes grown in North America arrived through European settlement and not independently from the South American sources. Still, one wild potato species, Solanum fendleri, is found as far north as Texas and used in breeding for resistance to a nematode species attacking cultivated potatoes. A secondary center of genetic variability of the potato is Mexico, where important wild species are found that have been used extensively in modern breeding, such as the hexaploid Solanum demissum, as a source of resistance to the devastating late blight disease.
The potato became an important staple crop in northern Europe as the climate changed due to the Little Ice Age, when traditional crops in this region did not produce as reliably as before. At times when and where most other crops would fail, potatoes could still typically be relied upon to contribute adequately to food supplies during the colder years. The potato was not popular in France during this time, and it is believed that some of the infamous famines could have been lessened if French farmers had adopted it. Today, the potato forms an important part of the traditional cuisine of the British Isles, northern Europe, central Europe and eastern Europe. As of 2007, Germany has a higher consumption of potato per capita than any other country.