A clarification that echoes the one made for tea in this atlas: just as 'tea' here denotes Camellia sinensis and not the many other plants steeped in hot water under that borrowed name, 'spinach' here means Spinacia oleracea and nothing else. This matters because a persistent confusion runs through the popular and even the scholarly literature: ancient Greek and Roman food writing is regularly cited as evidence for spinach in the classical world, yet the relevant texts describe no such plant. The Greek collective term horta (χόρτα) denotes any edible green gathered from field or hillside — orache (Atriplex hortensis), mallow (Malva species), blite (Chenopodium species), ground elder (Aegopodium podagraria), nettles, sorrel, and dozens of others — none of which are Spinacia oleracea. The Romans had similarly many olera (potherbs) but no spinach among them; the word 'Spinacia' does not appear in any classical Latin source because the plant had not arrived. The earliest unambiguous references to cultivated true spinach in Mediterranean or European writing date to Arab agricultural texts of the 9th century CE, by which time the plant had been in Arab cultivation for some generations and in Persian cultivation for considerably longer. This entry covers Spinacia oleracea from its domestication in Persia to its global diffusion; other plants sometimes called 'spinach' in English — Malabar spinach (Basella alba), New Zealand spinach (Tetragonia tetragonioides), and water spinach or kangkong (Ipomoea aquatica) — are unrelated species from different plant families, and they appear in this atlas only when they arise naturally in the cooking traditions of other ingredients.

Spinacia oleracea is an annual or biennial herb of the goosefoot family, Amaranthaceae, whose wild ancestor Spinacia tetrandra is native to the rocky, semi-arid slopes and steppe margins of the Iranian Plateau and the adjacent highlands stretching through Afghanistan and into Central Asia. The cultivated form was domesticated from this wild progenitor within that same region; the precise moment is impossible to recover, since the relevant Persian records are sparse and the earliest explicit descriptions of the plant arrive already filtered through Arab and Chinese sources. The Chinese Tang Dynasty text Shiyi Bencao (食疗本草, dietary supplement text, c. 7th century CE) records that spinach was brought to China as a diplomatic gift from the land of 'Boluo' — understood by later scholars to mean Nepal, or the broader northwest Indian sphere — during the reign of Emperor Taizong (r. 626–649 CE), implying that the plant was already being cultivated somewhere between Persia and the Indian subcontinent by at least the early 7th century CE, and in Persia itself probably well before that.

Spinacia oleracea is unusual among major leaf vegetables in having separate male and female plants (it is dioecious), and the seeds of some varieties bear prominent spines — a feature that may have given the plant its name in the European linguistic chain that derived ultimately from Persian. The plant is a cool-season annual that thrives in the temperature range of 10–20°C and bolts to flower rapidly in the heat of summer, a trait that continues to define where it is grown seasonally and commercially. Its leaves are rich in iron, folate, and vitamins A, C, and K, as well as in oxalic acid, which binds to some minerals and reduces their bioavailability; the popular belief, partly traceable to a misprint in a 19th-century German study, that spinach has an exceptionally high iron content beyond other leafy vegetables is now understood to be an error.

Cultivar groups within Spinacia oleracea include the savoy types (heavily crinkled, textured leaves, preferred in northern Europe and the United States for fresh market), the smooth or flat-leaf types (larger, easier to wash and process, preferred for canning, freezing, and the baby-leaf market), and the semi-savoy types (a compromise between the two). These cultivar groups have no separate geographic origins; they represent divergence through centuries of selection within a single domesticated species, and they do not warrant separate journey points on the spinach atlas.

The journey of spinach from its Persian origin to its position as one of the most widely grown leafy vegetables on earth took approximately fourteen centuries and followed three independent vectors: the Arab expansion westward through North Africa and into Iberia and Sicily; the Silk Road eastward to Tang Dynasty China and from there to Japan; and the Persian overland routes southward into the Indian subcontinent. These three arms of the spinach's diffusion produced the three great culinary traditions of the plant — the Persian-Indian tradition of long-cooked spinach in dairy and spiced sauces; the Arab-Mediterranean tradition of spinach with chickpeas and dried fruits; and the East Asian tradition of briefly cooked spinach dressed with sesame and soy — each one distinctive enough that a cook from one tradition would barely recognise the plant's role in the other two.

The Arab vector was the most consequential for European food history. Arab agricultural scientists of the Abbasid Caliphate (750–1258 CE) described spinach as 'isfanāj' (إسفناج), clearly identifying it as a Persian plant that the Arabs had adopted into their own kitchens and carried westward with their expansion across North Africa. The agricultural texts of al-Andalus — principally Ibn al-Awwam's Kitāb al-Filāḥa (Book of Agriculture, 12th century Seville) — describe its cultivation in the gardens of Islamic Iberia; from there it entered the Norman court of Sicily, where Arab gardeners continued to cultivate the plants they had grown under the preceding Sicilian emirate, and from Sicily it spread northward into the Christian kitchens of medieval Europe. The Crusaders returned from the Levant with spinach seeds as well, and the conjunction of these two channels — Mediterranean/Sicilian diffusion and Crusader return — meant that spinach was known in French, English, and German cooking by the mid-14th century, appearing in the English recipe collection known as The Forme of Cury (c. 1390) as 'spynoches' and in German records of similar date.

The Renaissance court of Florence developed a particular association with spinach, codified in the culinary term 'à la Florentine' that the French kitchen applied to any dish incorporating creamed spinach. The precise role of Catherine de Medici, who married the future Henry II of France in 1533, in introducing this association is much debated; the story that she brought Florentine cooks and Florentine spinach preferences to the French court is probably considerably embellished. What is clear is that northern Italian Renaissance cooking had genuinely elevated spinach as a refined ingredient by the mid-16th century, and that the 'à la Florentine' designation in French cuisine reflects a real cultural transfer, whatever the degree to which it was specifically Catherine de Medici's doing.

The Ottoman kitchen absorbed spinach from the Arab culinary world of Anatolia, where the plant had been cultivated since the Arab expansion of the 7th and 8th centuries CE. The Ottoman börek tradition developed the spinach and cheese filling as one of its most important forms; the Greek spanakopita, the defining spinach dish of the modern Aegean world, descends from this Ottoman börek tradition rather than from any ancient Greek use of the plant, because ancient Greece, as noted above, had no Spinacia oleracea. It arrived in Greece through the Ottoman cultural sphere, and the filo pastry technique itself is an Ottoman inheritance.

The East Asian journey began in 647 CE when King Narendradeva of Nepal sent spinach as a diplomatic gift to the Tang Emperor Taizong at Chang'an. From China's Silk Road capital the plant spread gradually through Chinese agriculture, becoming the 菠菜 (bōcài) of Chinese kitchens, and reached Japan during the Edo period — first cultivated there around 1688 — where it became the ほうれん草 (hōrensō) of the Japanese table. Both the Chinese and Japanese traditions favour briefly cooked spinach dressed lightly with garlic, sesame, soy, and dashi, in striking contrast to the long-cooked, heavily spiced Indian and Persian traditions.

In India, the spinach plant and the word 'palak' (पालक) — an independent Sanskrit-derived name with no etymological relationship to the Persian 'esfanāj' — suggest a long-established cultivation tradition, though the precise date of introduction from Persia or Central Asia is unknown. What is certain is that by the Mughal period spinach had become deeply embedded in the northern Indian kitchen, particularly in the creamy leaf preparations such as palak paneer that would eventually become the most internationally recognised Indian vegetable dish.

European colonial settlement carried spinach to the Americas from the 16th century onward; Martha Washington's cookbook contains spinach recipes, and the American creamed spinach that became a steakhouse staple reflects the French-influenced cooking of the eastern seaboard. The cultural moment that more than any other defined spinach's place in the modern American imagination came in 1929, when the cartoonist E. C. Segar gave his character Popeye an inexhaustible appetite for tinned spinach; the subsequent decades saw spinach consumption in the United States rise markedly. Today the Salinas Valley of California is among the world's foremost spinach-producing regions, and the commercial baby spinach market — smooth-leaf varieties harvested young, washed, and sold ready to eat — is a product of late-20th-century food processing and refrigerated logistics that has made the leaf a global salad standard.

Spinach is among the most widely cultivated leafy vegetables on earth, grown commercially on every inhabited continent and consumed in culinary traditions ranging from the Persian plateau to the Japanese archipelago. China is the world's overwhelmingly largest producer, accounting for more than ninety per cent of global output, followed at a considerable distance by the United States, Turkey, and Japan. In China the plant is eaten stir-fried with garlic, dissolved into congee, and added to dumplings; in Japan it is blanched and dressed with dashi or sesame paste in the ohitashi and goma-ae preparations that are among the most refined expressions of the vegetable in any cuisine; in South and Southeast Asia the related 'palak' tradition of long-cooked spinach in cream, yogurt, or lentil-based sauces produces some of the most complex preparations of the leaf.

In the Mediterranean world spinach remains important in both the Arab inheritance (espinacas con garbanzos in Seville, the spinach-filled börek of Turkey and the Levant) and the Greek tradition (spanakopita, spanakorizo). Italy maintains the spinach-ricotta partnership in pasta fillings and tarts that has been characteristic of the Italian kitchen since the medieval period. France upholds the 'à la Florentine' standard in its restaurant and home-cooking tradition, and creamed spinach has become the default accompaniment to beef in American steakhouses.

Nutritionally, spinach is valued for its folate, vitamin K, vitamin A, and antioxidant content, including lutein and zeaxanthin, which are associated with eye health. The widely circulated claim that spinach has exceptional iron content rests on a misprint in a 19th-century German study that placed the decimal point one position too far to the right; cooked spinach does contain useful iron but not the extraordinary quantity that Popeye and popular culture have attached to it. The oxalic acid in raw spinach also forms insoluble calcium oxalate, slightly reducing calcium absorption — a reason why briefly cooking or wilting spinach is nutritionally as well as culinarily sensible.