Morus, a genus of flowering plants in the family Moraceae, consists of 19 species of deciduous trees commonly known as mulberries, growing wild and under cultivation in many temperate world regions.[1][2][3][4] Generally, the genus has 64 subordinate taxa,[5] three of which are well-known and are ostensibly named for the fruit color of the best-known cultivar: white, red, and black mulberry (Morus alba, M. rubra, and M. nigra, respectively), with numerous cultivars and some taxa currently unchecked and awaiting taxonomic scrutiny.[6][5] M. alba is native to South Asia, but is widely distributed across Europe, Southern Africa, South America, and North America.[2] M. alba is also the species most preferred by the silkworm, and is regarded as an invasive species in Brazil and the United States.[2]
The closely related genus Broussonetia is also commonly known as mulberry, notably the paper mulberry (Broussonetia papyrifera).[7]
Despite their similar appearance, mulberries are not closely related to raspberries or blackberries. All three species belong to the Rosales order. But while the mulberry is a tree belonging to the Moraceae family (also including the fig, jackfruit, and other fruits), raspberries and blackberries are brambles and belong to the Rosaceae family.[8]
Mulberries are fast-growing when young, and can grow to 24 metres (79 feet) tall.[2][6] The leaves are alternately arranged, simple, and often lobed and serrated on the margin. Lobes are more common on juvenile shoots than on mature trees.[2][6] The trees can be monoecious or dioecious.[6]
The mulberry fruit is a multiple, about 2–3 centimetres (3⁄4–1+1⁄4 inches) long.[2][6] Immature fruits are white, green, or pale yellow.[6] The fruit turns from pink to red while ripening, then dark purple or black, and has a sweet flavor when fully ripe.[2][6]
The taxonomy of Morus is complex and disputed. Fossils of Morus appear in the Pliocene record of the Netherlands.[9] Over 150 species names have been published, and although differing sources may cite different selections of accepted names, less than 20 are accepted by the vast majority of botanical authorities. Morus classification is even further complicated by widespread hybridisation, wherein the hybrids are fertile.[citation needed]
The following species are accepted:[10]
Black, red, and white mulberries are widespread in Southern Europe, the Middle East, Northern Africa, and the Indian subcontinent, where the tree and the fruit have names under regional dialects. Black mulberry was imported to Britain in the 17th century in the hopes that it would be useful in the cultivation of silkworms.[11] It was much used in folk medicine, especially in the treatment of ringworms. Mulberries are also widespread in Greece, particularly in the Peloponnese, which in the Middle Ages was known as Morea, deriving from the Greek word for the tree (μουριά, mouria).
Mulberries can be grown from seed, and this is often advised, as seedling-grown trees are generally of better shape and health. Mulberry trees grown from seed can take up to ten years to bear fruit. Mulberries are most often planted from large cuttings, which root readily. The mulberry plants allowed to grow tall have a crown height of 1.5 to 1.8 m (5 to 6 ft) from ground level and a stem girth of 10–13 cm (4–5 in). They are specially raised with the help of well-grown saplings 8–10 months old of any of the varieties recommended for rainfed areas like S-13 (for red loamy soil) or S-34 (black cotton soil), which are tolerant to drought or soil-moisture stress conditions. Usually, the plantation is raised and in block formation with a spacing of 1.8 by 1.8 m (6 by 6 ft), or 2.4 by 2.4 m (8 by 8 ft), as plant-to-plant and row-to-row distances. The plants are usually pruned once a year during the monsoon season to a height of 1.5–1.8 m (5–6 ft) and allowed to grow with a maximum of 8–10 shoots at the crown. The leaves are harvested three or four times a year by a leaf-picking method under rain-fed or semi-arid conditions, depending on the monsoon. The tree branches pruned during the fall season (after the leaves have fallen) are cut and are used to make durable baskets supporting agriculture and animal husbandry.[citation needed]
Some North American cities have banned the planting of mulberries because of the large amounts of pollen they produce, posing a potential health hazard for some pollen allergy sufferers.[12] Actually, only the male mulberry trees produce pollen; this lightweight pollen can be inhaled deeply into the lungs, sometimes triggering asthma.[13][14] Conversely, female mulberry trees produce all-female flowers, which draw pollen and dust from the air. Because of this pollen-absorbing feature, all-female mulberry trees have an OPALS allergy scale rating of just 1 (lowest level of allergy potential), and some consider it "allergy-free".[13]
Mulberry tree scion wood can easily be grafted onto other mulberry trees during the winter, when the tree is dormant. One common scenario is converting a problematic male mulberry tree to an allergy-free female tree, by grafting all-female mulberry tree scions to a male mulberry that has been pruned back to the trunk.[15] However, any new growth from below the graft(s) must be removed, as they would be from the original male mulberry tree.[16]
All parts of the plant besides the ripe fruit contain a toxic milky sap.[17] Eating too many berries may have a laxative effect. Additionally, unripe green fruit may cause nausea, cramps, and a hallucinogenic effect.[18]
