Quinoa is not a grain at all, in the strict sense, but a pseudocereal: like buckwheat (see that entry) it is eaten as a grain yet belongs not to the grasses but to a broad-leaved family, the Amaranthaceae, which counts spinach, beetroot, chard, and amaranth among its members. Chenopodium quinoa is a goosefoot, its genus name built from the Greek for 'goose' and 'foot' after the shape of its leaves, and what it yields is not a true grain but a small, flat, disc-shaped seed borne in great dense panicles that ripen in colours from pale ivory through red to near-black. It was domesticated in the high Andes of South America, in the cold, thin air of the Altiplano above 3,500 metres where maize will not ripen and few crops survive, and it is supremely adapted to that punishing ground: tolerant of frost, drought, poor and saline soils, and the fierce ultraviolet light of the high plateau.

The seeds carry a natural defence that has shaped the whole human relationship with the plant: a coating of bitter compounds called saponins, soapy and astringent, which deter birds and must be washed or rubbed away before the seed can be eaten. Andean cooks have always rinsed quinoa in many changes of water, or abraded the coat off, and the saponin-rich rinsings were themselves put to use as a soap and a folk remedy. Cultivators long ago selected 'sweet', low-saponin types alongside the bitter ones, and the reduction of saponin content has been a central aim of modern breeding.

Quinoa is a single species, but it is not a single thing: over thousands of years of cultivation across the enormous range of Andean environments it diverged into several distinct ecotypes, each adapted to its own ground and each the basis of a regional variety still grown today. The highland or Altiplano type of the Titicaca basin is the heartland quinoa, the pale seed of the Peruvian and Bolivian plateau. The salares type of the southern Bolivian salt flats, grown on the mineral crust around the Salar de Uyuni, gives the large-grained Quinua Real, the 'Royal quinoa' prized above all others. The valley type of the moister inter-Andean valleys of Ecuador, Colombia, and northern Peru grows taller at lower altitude; and the coastal or sea-level type of south-central Chile, grown by the Mapuche far from the high plateau, is adapted to long summer days and low elevation, a quality that would prove decisive when, in the modern age, quinoa was at last carried to the temperate latitudes of the wider world.

For almost the whole of its history quinoa did not travel at all. It was the staff of life of the Andean highlands for five thousand years and more, the 'mother grain' of the Tiwanaku, the Wari, and the Inca, grown across the plateau and the valleys from southern Colombia to central Chile and north-western Argentina, but it was hemmed in by the very adaptations that made it: a crop of cold, high, short-day country that did not readily grow elsewhere, and a food so bound to indigenous Andean identity that the Spanish, on conquering the Inca empire in the sixteenth century, actively suppressed it. The conquistadors and the colonial church disdained quinoa as 'Indian food' and a prop of native religion and self-sufficiency; they tore up its fields, discouraged its sowing, and planted in its place the wheat and barley of Europe. Quinoa survived only because the highland communities kept growing it, quietly, in the remote reaches of the sierra where the colonial writ ran thin, and for four centuries it remained a poor people's food, all but unknown beyond the Andes.

Its journey to the world is therefore extraordinarily recent, a matter of decades rather than centuries. In the 1970s and 1980s a handful of North American enthusiasts carried Andean seed north and began to grow quinoa commercially in the high, cold San Luis Valley of Colorado, the first quinoa cultivated outside South America. From that beachhead, and on the rising tide of Western interest in health foods and plant protein, quinoa was discovered by the affluent kitchens of the global North as a 'superfood': gluten-free, high in protein, and carrying all nine of the essential amino acids in a balance rare among plant foods. The coastal Chilean ecotype, indifferent to daylength, proved the key that unlocked cultivation in the temperate world, and quinoa was soon being grown experimentally in North America, in Europe (in France, the Netherlands, and Britain), and later in India, China, and Australia.

The boom crowned itself when the United Nations declared 2013 the International Year of Quinoa, honouring the Andean peoples who had safeguarded the crop and proclaiming its promise for global food security. The surge in Western demand transformed the economics of the Andean Altiplano, bringing new income to quinoa farmers and, at the same time, raising hard questions about the rising local price of a food that had nourished those same communities for millennia. From a suppressed peasant grain of the high Andes, quinoa had become, within a single generation, a global commodity on the supermarket shelves and restaurant menus of the world.

Quinoa today lives a double life. In its Andean homeland it remains a genuine staple and a food of deep cultural identity, eaten across Peru, Bolivia, and Ecuador in the everyday soups, stews, and porridges of the sierra: the Peruvian sopa de quinua and the milk-and-cheese pesque, the Aymara steamed breads kispiña of the Bolivian salt flats, the sweet quinoa-and-milk drinks of the Ecuadorian highlands. Peru and Bolivia remain the world's largest producers by far, and the Bolivian Quinua Real of the Salar de Uyuni commands a premium as the finest large-grained quinoa in the world.

Beyond the Andes, quinoa is the emblematic health food of the early twenty-first century. In the kitchens of North America, Europe, and Australia it is treated as a virtuous, versatile grain substitute: simmered until the seeds uncurl their little white tails and tossed into salads, built into the vegetable-and-grain 'power bowls' and 'Buddha bowls' of the wellness table, spooned as a breakfast porridge, stuffed into peppers, and stirred into a gluten-free tabbouleh in place of bulgur. The red and black varieties, holding their shape and colour better than the white, have become favourites of the restaurant plate. Commercial cultivation has spread to Colorado and Canada, to France, the Netherlands, and Britain, to the Indian Himalaya, to China, and to Tasmania, though the Andes still grow the great bulk of the crop and the finest of it.

Nutritionally quinoa earns much of its reputation: it is a complete protein, rich in fibre, magnesium, iron, and B vitamins, naturally free of gluten, and quick to cook. It was studied by NASA in the 1990s as a candidate crop for sustaining astronauts on long missions, a measure of the regard in which its nutritional completeness is held. Its sudden global fame has been a mixed blessing for the Andean communities that gave it to the world, but it has also, after four centuries of neglect, restored the mother grain of the Inca to honour, and carried it from the thin air of the Altiplano to tables on every continent.