Morus (plant)

• 1. Introduction

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  Morus is a genus of deciduous trees with 19 species, and the three names most people attach to it are misleading. White, red and black mulberries are named for the color of their dormant buds, not for the color of their fruit. The genus is slippery in other ways too. It counts 64 subordinate taxa, and some of them are still waiting for botanists to examine them properly.

  These trees grow wild and under cultivation across many temperate regions of the world. Why has a single genus ended up woven into so many human trades, meals and stories? And why is it so hard to pin down on a botanist's list?

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• 2. Tangled Family Tree

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  More than 150 species names have been published for Morus, yet fewer than 20 are accepted by the vast majority of botanical authorities. Different sources cite different selections of accepted names, so the argument never fully closes. Hybridisation is widespread, and the hybrids are fertile, which blurs the lines between species even further. Fossils of Morus appear in the Pliocene record of the Netherlands, so the genus has a long history in the ground.

  Genome work is now catching up with the confusion. Chromosome-level genome assemblies have been published for Morus alba, Morus atropurpurea, Morus notabilis and Morus macroura. Together they give researchers shared resources for comparing species across the genus.

  Raspberries and blackberries look similar to mulberries, but they are only distant cousins. All three belong to the order Rosales. The mulberry is a tree in the family Moraceae, which also includes the fig and the jackfruit. Raspberries and blackberries are brambles in the family Rosaceae.

  The closely related genus Broussonetia is also called mulberry, most notably the paper mulberry, Broussonetia papyrifera. As for where the true Morus species live, the accepted list offers clues that range from Guizhou Province in China to Texas.

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• 3. Range and Invaders

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  The black mulberry, Morus nigra, belongs to Iran, the Caucasus and the Levant, while the red mulberry, Morus rubra, belongs to eastern North America. The long mulberry, Morus macroura, grows in Tibet, the Himalayas and Indochina. The Texas mulberry, Morus celtidifolia, reaches from the southwestern United States through Mexico and Central America into South America.

  In the 17th century, black mulberry was imported to Britain in the hope that it would help with raising silkworms. It also found a place in folk medicine, especially in the treatment of tapeworms.

  In Greece, the Peloponnese was known in the Middle Ages as Morea. The name comes from mouria, the Greek word for the tree.

  White mulberry has a harsher reputation in the Americas. In North America it is treated as an invasive exotic that has taken over extensive tracts from native plants, including the red mulberry. It is also regarded as invasive in Brazil. In Queensland and New South Wales it counts as an environmental weed, even though black, red and white Morus mulberries are common in Australian backyards.

  Australia's own trees called mulberries, Hedycarya angustifolia and Pipturus argenteus, belong to families other than Moraceae. The invasive white mulberry, meanwhile, is the very species that silkworms prefer to eat.

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• 4. Silk's Only Menu

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  The silkworm, Bombyx mori, carries the mulberry genus in its own scientific name. Mulberry leaves, particularly those of the white mulberry, are its sole food source, and its cocoon is the raw material for silk. The wild silk moth eats mulberry too. So do other Lepidoptera larvae, including the common emerald, the lime hawk-moth, the sycamore moth and the fall webworm.

  By at least 220 AD, Emperor Elagabalus was wearing a silk robe. The Ancient Greeks and Romans cultivated the mulberry for silkworms. English clergy wore silk vestments from about 1500 onwards, and mulberry and the silk industry played a role in colonial Virginia.

  Silk was not the only thing people took from the tree. Buddhist monks of the Khmer Empire found a different use for its bark.

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• 5. Paper, Baskets, Barrels

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  During the Angkorian age of the Khmer Empire in Southeast Asia, monks at Buddhist temples made paper from mulberry bark. They used it to make books known as kraing.

  Tengujo, made in Japan, is the thinnest paper in the world, and it is produced from kozo, the stems of mulberry trees. Traditional Japanese washi paper is often made from parts of the same tree.

  On farms, the leaves are picked three or four times a year under rain-fed or semi-arid conditions, depending on the monsoon, and serve as animal fodder. Branches pruned in the fall, after the leaves have dropped, are cut and made into durable baskets that support agriculture and animal husbandry.

  The wood has a place in the cellar as well. Barrels of mulberry wood are used to age Țuică, a traditional Romanian plum brandy. Mulberry's reach into drinking does not stop there.

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• 6. Fruit and Pigment

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  A ripe mulberry becomes plump, succulent and juicy, resembling a blackberry, but its color does not reveal its species. Fruit may be white, lavender or black. Black mulberries are large and juicy with a balance of sweetness and tartness. Red mulberries are deep red, sweet and juicy. White mulberries are typically sweet but not tart.

  The East Asian white mulberry, widely naturalized in urban eastern North America, tastes different again. It is sometimes described as refreshing and a little tart, with a bit of gumminess and a hint of vanilla.

  Cooks use the fruit in pies, tarts, wines, cordials and herbal teas. In the Old World, jams and sherbets are often made from it. In spring, the new tender twigs are semisweet and can be eaten raw or cooked. In Armenia, mulberries go into homemade moonshine called tti oghi and into a syrup called doshab.

  Raw mulberries are 88% water, 10% carbohydrates, 1% protein and less than 1% fat. A 100 g portion supplies 43 calories, 44% of the Daily Value for vitamin C and 14% for iron. The fruit and leaves are also sold in various forms as dietary supplements.

  Anthocyanins give the fruit its color, and their effects in humans are unknown. These water-soluble pigments are easy to extract, which makes them useful as natural food colorants. Scientists tested 31 Chinese mulberry cultivars and found anthocyanin yields from 148-2725 mg/L of fruit juice. The sugars, acids and vitamins stayed intact in the leftover juice, and the extract could also serve as a fabric dye.

  Not every part of the tree is as gentle as its ripe fruit, as the milky sap shows.

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• 7. Cultivation and Cautions

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  Milky latex can ooze from every part of the plant except the ripe fruit. It is mildly toxic if swallowed, causing digestive distress and, at larger doses, hallucinations. It also irritates the skin and may cause a rash. Unripe green fruit may bring nausea and cramps and can be hallucinogenic, while eating too many ripe berries has a laxative effect.

  Some North American cities have banned planting mulberries because of the pollen. Only male trees produce it, and the lightweight grains can be inhaled deeply into the lungs, sometimes triggering asthma. Female trees bear all-female flowers that draw pollen and dust out of the air. On the OPALS allergy scale they rate just 1, the lowest level, and some people call them allergy-free.

  That difference explains a gardener's trick. Because mulberries can be monoecious or dioecious, a problematic male tree can be cut back to the trunk in winter, when it is dormant. All-female scion wood is then grafted on. Any new growth from below the graft must be removed, because it would come from the original male tree.

  Mulberries can be grown from seed, and seedling trees are generally of better shape and health. A tree from seed can take up to ten years to bear fruit. Most plantings start instead from large cuttings, which root readily. Young trees grow fast and can reach 24 m tall.

  In rainfed regions, growers raise saplings 8-10 months old, such as the variety S-13 for red loamy soil or S-34 for black cotton soil. Both tolerate drought. Plants are spaced 6 by 6 ft or 8 by 8 ft and pruned once a year during the monsoon to 5-6 ft, keeping at most 8-10 shoots at the crown.

  The fruit's color has an older explanation than any of this, and it comes from Babylonian myth.

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• 8. Blood-Red Stories

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  A Babylonian myth, later taken up by Ovid in his Metamorphoses, explains the reddish-purple of mulberries through the lovers Pyramus and Thisbe. They meet under a mulberry tree, probably the native Morus nigra. Pyramus finds Thisbe's bloodstained cloak and believes a lion has killed her, so he takes his own life with a sword. Thisbe then does the same. Their blood splashes the previously white fruit, and the gods change its color forever to honour their forbidden love.

  The Old Testament's 1 Maccabees puts the fruit on a battlefield. The Seleucids used the "blood of grapes and mulberries" to provoke their war elephants before fighting Jewish rebels.

  The tree also sits at the center of a children's rhyme. "Here We Go Round the Mulberry Bush" uses it in the refrain, and so do some contemporary American versions of "Pop Goes the Weasel".

  In 1889, Vincent van Gogh painted the tree in The Mulberry Tree, titled Mûrier in French, and he featured it in some of his other paintings as well.

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