Spinach (Spinacia oleracea, L. 1753)

Identity

Spinach (Spinacia oleracea L., 1753) is an annual leafy vegetable in the Amaranthaceae family and the genus Spinacia. It is grown for its tender, green, nutritious leaves, eaten raw in salads or cooked. A cool-season plant, it performs best in spring and fall rather than summer heat. ^{3 4}

The epithet oleracea means “of the vegetable garden” in Latin and neatly reflects its status. Spinach is a cultigen, a plant known only in cultivation, with no clearly identified wild population. Described by Linnaeus in 1753, it is now one of the most widely grown leafy vegetables in temperate climates. ^{1 2}

Recognition

Young spinach begins as a rosette of long-stalked leaves arising from the crown at ground level. The tender, bright green blades may be smooth or savoyed, depending on the variety. They range from rounded to arrow-shaped and are often 3–8 cm (1–3 in) long. At the harvesting stage, the plant remains low, about 15–30 cm (6–12 in) tall. ^{6 3}

Heat or lengthening days prompt an upright flower stalk that can reach 30–60 cm (1–2 ft). This transition, called bolting, marks the end of the leaf-harvesting period. Small yellowish-green flowers have no showy petals or nectar, because wind carries their pollen rather than insect visitors. ^{6 4}

A useful botanical distinction is that spinach is generally dioecious, with separate male and female plants. This separation of the sexes is unusual among familiar vegetables and explains why the inconspicuous flowers differ from one plant to another. ^{6 5}

Useful taxonomy

Carl von Linnaeus described Spinacia oleracea in 1753, and it remains the accepted species name. The genus Spinacia is small; much of the diversity lies in cultivated varieties and a few infraspecific taxa. The principal names and ranks include:

• Spinacia oleracea subsp. oleracea, the nominal subspecies
• Spinacia oleracea subsp. turkestanica (Iljin) Del Guacchio & P.Caputo, a subspecies name
• Spinacia oleracea var. inermis (Moench) Peterm., a botanical variety name
• Spinacia oleracea var. spinosa (Moench) Peterm., another botanical variety name
• Spinacia inermis Moench, a historical scientific name

The accepted scientific name Spinacia oleracea is the reliable reference. Commercial names such as Matador and Monstrueux de Viroflay identify horticultural varieties, rather than separate species or botanical varieties. Spinach is now placed in Amaranthaceae, after long being included in the former Chenopodiaceae family. ^{1 3}

Habitat and range

Cultivation defines spinach's distribution: it derives from ancestors in Central and Southwest Asia, in a region extending from Iran to western Pakistan, but it is not known as a spontaneously occurring wild plant. Vegetable cultivation carried it from Asia toward the Mediterranean and then into medieval Europe. ^{1 4}

Its habitat is therefore the vegetable garden or cultivated field. It is sown in rich, moisture-retentive soil in regions and seasons with moderate temperatures, around 10–20 °C (50–68 °F). Summer heat works against it and quickly triggers seed-stalk formation. ^{6 3}

Regions recorded for the species chiefly indicate areas of cultivation. Spinach is now produced across temperate climates, from China to North America and Europe, without establishing lasting naturalized populations. A map of its cultivation should not be read as a strict map of wild origins. ^{4 5}

Life cycle and reproduction

A short annual cycle takes spinach from seed to harvest. Direct-sown seeds emerge in one to two weeks at soil temperatures of 10–20 °C (50–68 °F), then develop a harvestable leaf rosette in six to ten weeks. Growth remains vigorous while conditions stay cool. ^{2 6}

Reproduction begins with bolting. In heat and long days, the plant stops producing tender leaves and raises a flower stalk. The small yellowish-green flowers are wind-pollinated, after which female plants bear small dry fruits containing the seeds. ^{6 4}

Growers propagate spinach only from seed; it is neither divided nor grown from cuttings. Successive sowings every two to three weeks in spring and late summer spread production through the cool season. Picking outer leaves individually extends harvesting, while the appearance of the flower stalk signals the end of its useful leaf-producing cycle. ^{2 5}

Uses and risks

Cooking and salads account for spinach's main use. Young, tender leaves are eaten raw or cooked as a vegetable, supplying vitamins and minerals in many dishes. It is an easy, productive garden crop valued for fast growth in cool weather. ^{3 2}

Leaf oxalates, or oxalic acid, are the main caution. In sensitive people, repeated heavy consumption may interfere with iron and calcium absorption and increase the risk of kidney stones; cooking reduces some of the oxalates. For most people, spinach remains a healthy food when eaten in moderation. It is not listed as a poisonous plant for cats and dogs, but its oxalate content calls for similar caution in vulnerable animals. ^{6 5}

Its reputation for being exceptionally rich in iron needs qualification. That reputation rests partly on inflated figures circulated in the 20th century. Its actual iron content is respectable but comparable to other leafy vegetables, and oxalates limit absorption of some of that iron. ⁴

Varieties, look-alikes and related plants

Cultivar names describe garden selections rather than separate species. Matador and Géant d'hiver are slow-bolting types, the latter sown in fall. Monstrueux de Viroflay is an old variety with very large leaves, while America has thick, savoyed foliage. Match the variety to the intended season and its resistance to bolting before sowing. ²

Several vegetables sold as “spinach” do not belong to the genus Spinacia. Common garden comparisons include:

• Tetragonia tetragonioides, New Zealand spinach, a heat-tolerant summer vegetable;
• Basella alba, Malabar spinach, a climbing vine from warm regions;
• Beta vulgaris var. cicla, chard, another leafy vegetable in the Amaranthaceae family.

These plants share a culinary role with spinach, but their thicker foliage and tolerance of heat distinguish them from true spinach, a characteristic cool-season crop. Their familiar market names therefore describe use rather than close botanical identity. ^{3 6}

Main sources

• Plants of the World Online / Kew, Spinacia oleracea L.
• Royal Horticultural Society, Spinach - grow your own
• Missouri Botanical Garden, Spinacia oleracea
• Encyclopaedia Britannica, spinach
• Plants For A Future, Spinacia oleracea
• NC State Extension, Spinacia oleracea
• USDA PLANTS Database, Spinacia oleracea L.