Tarragon is the sweet exception in a famously bitter family. Its genus, Artemisia, is the great clan of the wormwoods, the mugworts, the southernwood, the sagebrush of the American West, and the absinthe of the bottle, plants prized for a bitterness so penetrating that the genus is named for Artemis, goddess of the wild. Almost alone amongst them, Artemisia dracunculus turned not bitter but sweet, developing in its leaves the aromatic compound estragole, the same anise-and-liquorice note that scents fennel and chervil, and so became the one member of the wormwood tribe to earn a place at the table rather than in the medicine chest.

The wild plant is a slender, branching perennial of the open steppe, and its range is enormous: it grows wild in a broad belt across Central Asia, Mongolia, and southern Siberia, and, remarkably, across much of western North America as well, one of the few culinary herbs native to both the Old World and the New. Yet the tarragon of the kitchen is a far narrower thing. The prized culinary herb, French tarragon (var. sativa), is a sterile clone that almost never flowers and sets no viable seed; it can be propagated only by cuttings or division, passed hand to hand from one garden to the next, and it carries the intense, refined, sweetly aniseed flavour on which French cooking depends. Beside it grows Russian tarragon, the coarse, hardy, seed-grown form of the same species, vigorous and frost-proof but so much milder, and often faintly bitter, that cooks dismiss it as a poor relation.

A third plant entirely, gathered under the same name, belongs to the New World and to a different family altogether. Mexican tarragon, Tagetes lucida, is a marigold, an aster-family cousin of the African and French marigolds of the flower bed, native to the highlands of Mexico and Guatemala. It happens to have evolved the same estragole-scented anise note as true tarragon, and in the heat of the tropics, where the sterile French clone languishes and dies, it serves as the tarragon of the warm countries: the pericón of the Mexican kitchen and the yauhtli of the Aztecs before them.

Tarragon has the strangest itinerary of all the great kitchen herbs, for it is the one the classical Mediterranean never knew. There is no tarragon in the Greek herbals, none in the Roman cookery of Apicius, no Latin name for it amongst the named herbs of antiquity; the plant of the eastern steppe simply did not reach the Mediterranean in the age of Greece and Rome. It arrived, instead, in the Middle Ages, and it came by way of the Arabs.

The sweet clone, selected somewhere in the Central Asian and Persian world from the wild dragon-herb of the steppe, spread west into the Persian and Caucasian kitchen, where the fresh leaf, tarkhun, became one of the essential herbs of the raw herb platter and the pickle jar. From the Persianate world the Arabs took up the plant and its name: the thirteenth-century Andalusian botanist Ibn al-Baytar described it as ṭarḫūn, and it was through the Arabic word, carried into Moorish Spain and thence into the Romance languages, that medieval Europe at last received both the herb and a name for it. In France the herb found its true home. By the Renaissance it had become the king of the French kitchen garden, the soul of the fines herbes and the defining flavour of the sauce béarnaise, and from the French table it spread into the whole of European haute cuisine and, with it, across the Atlantic to America, where it flavours the Green Goddess dressing of San Francisco. A separate sweet turn took it into the Alpine and Pannonian lands, where Slovenia folds it into the festive rolled cake, the potica.

In the East the herb never left. The Caucasus made it the basis of one of the most beloved soft drinks of the entire Soviet world, the bright green Tarkhuna soda invented in Tiflis in 1887, and the kitchens of Georgia, Armenia, and Azerbaijan use the fresh leaf with a freedom unknown in the West, above all in the Georgian spring stew chakapuli. And in the New World, quite independently of all of this, the Aztecs had long since taken up their own anise-scented herb, the marigold yauhtli, which the Spanish renamed pericón and the modern world calls Mexican tarragon: the same flavour, reached by a different plant on the far side of the world.

Tarragon's culinary geography divides cleanly into three worlds. The first is France and the cuisine that descends from it, where tarragon is the indispensable fine herb: one of the four fines herbes alongside chervil, chives, and parsley, the herb without which there is no sauce béarnaise, no poulet à l'estragon, no sauce gribiche or ravigote, and no proper tarragon vinegar. French cooking treats tarragon as a primary flavour of distinction, and the herb remains most strongly associated, in the Western mind, with the refinement of the French table. The herb's anise sweetness has a particular affinity for eggs, chicken, fish, and cream, and it is the classic partner of the first two above all.

The second world is the Caucasus, Persia, and the lands of the former Soviet Union, where tarragon is used fresh and in quantity. In Iran and Azerbaijan the leaf, tarkhun, is eaten raw by the handful in the sabzi khordan, the platter of fresh herbs set on every table, and folded into pickles and egg dishes; in Georgia it flavours the spring stew chakapuli and is bottled as the luminous green Tarkhuna soda that, across Russia and the Caucasus, carries a powerful charge of Soviet-era nostalgia. The hardy Russian tarragon, grown from seed, is the form most cultivated across this cold and continental region.

The third world is the New World, where two quite different tarragons are used. French tarragon, carried from Europe, is the herb of North American and Australian cooking, of the Green Goddess dressing and the tarragon chicken salad; whilst in Mexico and the warm countries, where the sterile French clone cannot endure the heat, the native marigold Mexican tarragon (Tagetes lucida), the pericón, takes its place, brewed into a digestive tea, used to flavour fresh corn, and laid in protective crosses across the fields on its feast days. France remains the spiritual home of the culinary herb, but tarragon, in one form or another, is now grown and eaten across every temperate and highland region of the world.