Black mulberry (Morus nigra, L. 1753)

Identity

Black mulberry (Morus nigra L., 1753) is a deciduous fruit tree in the Moraceae family and the genus Morus. Cultivation in southwestern Asia goes back so far that its strictly wild range can no longer be defined. It is grown for its edible fruit, fleshy and dark red to black, with a sweet-tart flavor when ripe in late summer. ^{1 3}

Whether planted in an orchard or a garden, black mulberry develops a stocky, spreading shape and an often twisted trunk, gaining ornamental character with age. The names black mulberry and Persian mulberry reflect its fruit color and West Asian origins. Its fruit is sometimes called a blackberry, although that name also refers to the unrelated fruit of brambles. ^{2 4}

Recognition

Rough, heart-shaped leaves with distinctly toothed margins provide an immediate clue to Morus nigra. They are dull green above, paler and slightly hairy below, and turn yellow in fall. A broad, low crown sits above a thick, knotted trunk with fissured, orange-brown bark. ^{2 4}

The clearest identifying feature is its fruit: a sorosis, a fleshy multiple fruit measuring 2 to 3 cm (0.8 to 1.2 in), made up of many small fused units. Green at first, it turns red and then very dark red, almost black, at maturity. The juicy, sweet-tart flesh releases a purplish-red juice that strongly stains fingers. Like other Moraceae, the tree exudes milky sap whenever a twig or leaf is wounded. ^{3 4}

Mature black mulberry trees commonly reach 8 to 12 m (26 to 39 ft) tall with a comparable spread, becoming larger with age. Their spring flowers, borne in small greenish catkins and pollinated by wind, are easily overlooked. ^{2 3}

Useful taxonomy

Linnaeus described black mulberry in 1753 as Morus nigra L. A profusion of regional names and horticultural varieties has long complicated the taxonomy of Morus, and several older synonyms remain in circulation. The main names to recognize are:

• Morus laciniata Mill.
• Morus siciliana Mill.
• Morus petiolaris Raf.

• Morus nigra var. laciniata (Mill.) Moretti

• Morus cretica Raf.

One striking biological feature is black mulberry's exceptionally high chromosome number among seed plants. This results from extensive polyploidy and sets it apart from other species in the genus. The accepted scientific name, Morus nigra, remains the reliable reference: labels such as Chelsea and Jerusalem identify horticultural selections, not separate species. ^{1 5}

Habitat and range

Southwestern Asia is the area of origin of Morus nigra, particularly western and southwestern Iran and Asia Minor, where it has been cultivated since antiquity. Its long domestication has blurred the boundaries of its wild range so thoroughly that these can no longer be located with certainty. ^{1 3}

From its West Asian center, the tree spread westward in antiquity, reaching the Mediterranean basin and later warm temperate regions more widely. It became particularly important in Italy, where it was planted for silk production before white mulberry, better suited to silkworm feeding, replaced it. ^{3 6}

Most black mulberries encountered today are planted trees in orchards, gardens, rows or parks, growing in deep, well-drained soil in warm positions. The species rarely naturalizes and does not form substantial spontaneous stands, unlike genuinely wild species. ^{2 4}

Life cycle and reproduction

Seasonal changes shape this deciduous tree's life cycle: buds open and flowers appear in spring, fruit develops in summer, and leaves turn distinctly yellow before falling in autumn. The inconspicuous flowers form small greenish catkins and rely on wind pollination, with little involvement from insects. ^{2 4}

Each pollinated female inflorescence develops into a sorosis, the characteristic multiple fruit, swelling and darkening to red-black as it ripens. Ripe fruit is so delicate that it drops at the slightest touch and must be eaten quickly because it stores poorly. Ripening extends through late summer, sometimes into early autumn depending on the climate. ^{3 2}

Growers mainly propagate black mulberry from stem cuttings, which retain the qualities of a fruiting cultivar, or from seed that has first undergone cold stratification. Seed propagation is slower and produces variable results. Either route calls for patience: growth remains slow to moderate, and regular fruiting often takes 8 to 15 years in seed-grown trees, less in selected cuttings. The reward is a very long-lived tree capable of cropping for decades. ^{4 5}

Uses and risks

Eating the ripe fruit is the principal use of Morus nigra. It can be enjoyed fresh or cooked, in jam, syrup or baked goods. Its sweet, slightly tart flavor makes black mulberry one of the most valued orchard mulberries. Historically, the tree also supported silk production in the Mediterranean regions where it was introduced, before white mulberry replaced it as silkworm feed. ^{3 4}

For humans, fully ripe fruit is safe to eat. In contrast, unripe green fruit and raw milky sap from leaves and twigs may cause mild digestive upset or temporary irritation, so harvest only dark, soft fruit. The ASPCA also lists mulberry among plants whose unripe parts may upset pets if ingested; ripe fruit poses no serious risk to humans. In the garden, the main nuisance is practical: ripe fruit leaves lasting stains on paving, patios and clothing, making a position away from walkways preferable. ^{7 2}

Varieties, look-alikes and related plants

Nursery offerings are fruiting selections rather than separate species. Chelsea and Jerusalem are fertile, large-fruited cultivars selected for flavor and relatively early cropping. King James refers to an old English line associated with 17th-century plantings. Before buying, check the cultivar, its hardiness and its ability to fruit in your climate.

Several plants are commonly confused with black mulberry:

• Morus alba, white mulberry, has smoother leaves and often pale fruit, and is cultivated to feed silkworms;
• Rubus fruticosus, a bramble, bears blackberries on a thorny shrub in the rose family rather than on a tree;
• Morus rubra, red mulberry from North America, is another species in the genus with comparable fruit.

Red-black fruit formed as a sorosis, rough heart-shaped leaves and milky sap remain the most reliable clues for identifying black mulberry, Morus nigra. ^{1 3}

Main sources

• Plants of the World Online / Kew, Morus nigra L.
• Royal Horticultural Society, Morus nigra Chelsea
• Encyclopaedia Britannica, black mulberry
• Plants For A Future, Morus nigra
• USDA GRIN Taxonomy, Morus nigra L.
• Integrated Taxonomic Information System, Morus nigra L.
• ASPCA, mulberry tree toxicity entry