Morus, commonly known as mulberry, is a genus of 17–19 accepted species of deciduous trees in the family Moraceae, order Rosales. First described by Linnaeus in his Species Plantarum (1753), the genus has a broad native range stretching from Iran east to the Kuril Islands, through Western Malesia, and into North, Central, and Western South America. More than 100 further regions have been colonized through introduction, making mulberries among the most cosmopolitan of fruiting trees.
Trees grow rapidly when young, with some individuals reaching 24 meters in height. The leaves are alternately arranged, simple, often lobed and serrated — the lobes most prominent on juvenile shoots. Plants may be monoecious or dioecious. The characteristic fruit is a compound structure 2–3 cm long, transitioning in color from white or pale green when immature to pink-red and finally dark purple or black at full ripeness, when the flavor becomes sweet and rich.
Mulberries have been intertwined with human civilization for millennia, chiefly through their role in sericulture. The leaves of Morus alba (white mulberry) are the sole food source of the silkworm (Bombyx mori), and the genus has been cultivated across Asia, the Middle East, and Europe for silk production since antiquity. The Peloponnese peninsula was known as "Morea" in the Middle Ages, a name derived from the Greek word for mulberry (μουριά), reflecting how deeply the tree was embedded in regional culture and economy.
All parts of the plant except the ripe fruit can exude a milky latex that is mildly toxic if ingested. Unripe fruits may cause nausea and, reportedly, hallucinogenic effects. Male trees are notable for producing abundant airborne pollen that can trigger asthma, leading some North American municipalities to ban their planting; female trees rate only 1 on the OPALS allergy scale.
Despite widespread cultivation, the genus contains a conservation concern: Morus alba, introduced globally for silk production, has escaped into natural areas and hybridizes freely with the native North American Morus rubra (red mulberry), threatening the latter's genetic integrity and contributing to its endangered status in Ontario, Canada.
Etymology
The genus name Morus is the classical Latin word for mulberry, derived from the ancient Greek moron (μόρον). The Greek word also gave rise to the medieval name "Morea" for the Peloponnese peninsula of Greece, which was densely planted with mulberries during the Byzantine period to support silk production. The dark red or purple color of ripe mulberry fruit features in classical mythology: the Roman poet Ovid, drawing on a Babylonian original, recounts how the fruit of the mulberry tree was stained dark by the blood of the tragic lovers Pyramus and Thisbe, explaining why the berries that were once white turn reddish-purple when ripe.
Distribution
The native range of Morus spans from Iran east to the Kuril Islands, encompassing Central Asia, the Indian subcontinent, East and Southeast Asia, and Western Malesia, with additional native populations in North America, Central America, and Western South America. Morus rubra (red mulberry) is native to eastern North America, and Morus nigra (black mulberry) is native to Iran, the Caucasus, and the Levant region.
Through millennia of cultivation for sericulture and fruit, mulberries have been introduced to over 100 regions beyond their native range, including throughout Europe, Africa, the Pacific islands, and the Caribbean. Morus alba (white mulberry) is now naturalized across much of the globe and is particularly widespread in North America, where it escaped cultivation in the late 19th century and has spread through urban, agricultural, and disturbed environments.
Ecology
Mulberry leaves are ecologically critical as the sole larval food source of the domesticated silkworm (Bombyx mori), particularly the leaves of Morus alba. Various wild Lepidoptera also feed on mulberry foliage. The ripe fruits are consumed by a wide range of birds and mammals, aiding seed dispersal.
All parts of the plant except ripe fruit can produce a milky latex that is mildly toxic to humans and animals if ingested. Unripe fruits may cause digestive upset. The ripe berries themselves have mild laxative properties.
Male mulberry trees are significant producers of airborne pollen and are associated with allergic asthma in susceptible individuals. This has led several North American cities to restrict or ban the planting of male trees. Female trees are much less allergenic, rated 1 (lowest) on the OPALS allergy scale.
Introduced populations of Morus alba pose a significant ecological threat in North America: the species hybridizes readily with the native Morus rubra, altering the latter's genetic integrity, transmitting root disease to it, and outcompeting it in urban and disturbed habitats. This interaction has contributed to the endangerment of Morus rubra in Ontario, Canada, and to conservation concern in several US states.
Cultivation
Mulberries are adaptable trees that grow in a wide range of soils but perform best in warm, well-drained loamy soil in a sunny position. They tolerate semi-shade and drought and have good wind resistance, though prolonged maritime exposure can damage branches. Most species are hardy across USDA zones 4–10.
In commercial silkworm farming, trees are spaced approximately 1.8×1.8 m or 2.4×2.4 m, and crowns are pruned annually during the monsoon season to maintain a height of 1.5–1.8 m with 8–10 productive shoots. Leaves are typically harvested three to four times per year. Pruned branch material is traditionally used for basket weaving.
Grafting is commonly practiced: scion wood grafts readily onto rootstock during winter dormancy, enabling horticulturalists to convert allergenic male trees into fruiting female trees. The wood is valued for sports equipment and furniture manufacture. Bark fiber has traditional uses in weaving and papermaking, and a brown dye can be extracted from the trunk.
Propagation
Mulberries can be propagated from seed, cuttings, or grafts. Seeds require 2–3 months of cold stratification before germination; they are typically sown in February in cold frames. Seed-grown trees may take up to ten years to begin fruiting and can display variable form and health, though seedlings sometimes exhibit better vigour than clonally propagated plants.
Vegetative propagation is more common in practice. Half-ripe cuttings (7–10 cm with a heel) taken in July or August root reliably. Mature hardwood cuttings, 25–30 cm long, taken in autumn or early spring and buried three-quarters of their length in a nursery bed, are a traditional and effective method. Grafting of scion wood onto established mulberry rootstock is performed during winter dormancy and allows rapid establishment of known cultivars.
Conservation
Morus rubra (red mulberry), native to eastern North America, is listed as endangered in Canada (Ontario), primarily due to hybridization with and displacement by the introduced Morus alba. The two species interbreed freely wherever their ranges overlap, and the resulting hybrids can transmit root diseases to pure M. rubra populations. The species is of conservation concern in several US states including Connecticut, Massachusetts, Vermont, and Michigan.
Morus alba itself is classified as a Category 4 invasive species in the Great Lakes States and is subject to Category 3 restrictions in South Africa. Management of invasive populations relies on mechanical removal (hand-pulling, cutting, grinding), stump girdling, and application of systemic herbicide (glyphosate) to freshly cut stumps to prevent resprouting.
At the genus level, most other Morus species have not been comprehensively assessed for global conservation status. The primary threat to genus-level diversity is genetic erosion of native species through hybridization with widely naturalized M. alba.
Cultural Uses
Sericulture — the production of silk — is the most historically significant use of the genus. Mulberry leaves, especially those of Morus alba, are the exclusive food of the domesticated silkworm (Bombyx mori), and the cultivation of mulberries for this purpose shaped economies and trade routes from ancient China through the Byzantine Empire and into early modern Europe. Emperor Elagabalus was reportedly wearing silk robes by 220 AD; English clergy adopted silk vestments around 1500.
The fruit of all mulberry species is edible and widely consumed fresh, or processed into pies, tarts, wines, cordials, herbal teas, jams, and sherbets. Raw mulberries are nutritious: per 100 g they supply approximately 43 kcal, 44% of the daily value for vitamin C, and 14% of the daily value for iron. Anthocyanins extracted from the fruit are used as natural food colorants; yields from Chinese cultivars range from 148 to 2725 mg/L.
Young mulberry leaves and shoots are eaten as cooked vegetables in parts of Asia. The inner bark has historically been roasted and ground into a meal for soups or bread. Traditional medicine across Asia uses the leaves for colds, influenza, and eye infections; root bark preparations address respiratory conditions and hypertension; the fruit is used to support kidney function.
In Japan, mulberry stems (kozo) are used to produce washi paper and Tengujo, considered the world's thinnest paper. The wood has uses in barrel aging of spirits (including Țuică, a Romanian plum brandy) and in the manufacture of sports equipment. Mulberry bark fiber is woven into cloth and rope in various traditional crafts.
The tree has a long cultural presence in art and literature: Ovid's Metamorphoses tells the story of Pyramus and Thisbe beneath a mulberry tree; the English nursery rhyme "Here We Go Round the Mulberry Bush" references the tree; and Vincent van Gogh painted The Mulberry Tree in 1889 while at the Saint-Paul-de-Mausole asylum.
Taxonomy Notes
The genus Morus was formally established by Carl Linnaeus in Species Plantarum (1753, p. 986). It belongs to the family Moraceae (order Rosales, subclass Magnoliidae). The IPNI identifier is urn:lsid:ipni.org:names:30004492-2. POWO (Plants of the World Online, Kew) recognizes 17 accepted species following Govaerts et al. (2021); Wikipedia cites 19; species counts vary by dataset (4–38) depending on taxonomic treatment consulted, reflecting ongoing disagreement over species delimitation exacerbated by widespread interspecific hybridization.
Over 150 names have been formally published for members of this genus; most are synonyms. Hybridization between species is common and produces fertile offspring, significantly complicating classification. Recent whole-genome assemblies are available for M. alba, M. atropurpurea, M. notabilis, and M. macroura, providing molecular data to support future taxonomic revisions.
The genus name Morus L. (1753) is distinct from Morus Vieillot, 1816 — a bird genus (gannets, family Sulidae, order Suliformes) — which shares the same canonical name but belongs to the animal kingdom. Care is required when querying general biodiversity databases.
