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There are estimated to be about 475 species of Diospyros, most of them found in the Old World tropics, with a few in temperate areas. They are trees or shrubs, usually evergreen, although some temperate species are deciduous. The bark is often dark and deeply ridged. The shoots lack a terminal bud but the twigs sometimes terminate as a spine. The leaves are usually alternate, but may be opposite, and are simple and entire, held on a petiole. They are frequently somewhat foetid. In deciduous species they often turn a good yellow in autumn. The inflorescences are axillary, composed of one or a few flowers, borne at the base of the new shoots. The flowers are usually dioecious, and usually unisexual (but monoecious species or bisexual flowers are known), with three to five (to seven) calyx lobes fused at the base and a tubular corolla with three to five (to seven) lobes. In male flowers the stamens are usually in two whorls, two to four times more numerous than the corolla lobes. The female flowers are often solitary, with a whorl of staminodes inside the corolla tube, and a bifid stigma. The fruit is a fleshy or drier, leathery-textured berry, usually with the enlarged calyx persisting. The seeds are often flattened.
The genus Diospyros is an important source of fine timbers, including the original ebony (from the Sri Lankan Diospyros ebenum Koenig), and the tropical species can be impressively large trees. In the temperate zone the most familiar species are D. kaki the (Japanese) Persimmon or Sharon Fruit, D. lotus the Date Plum, and D. virginiana the (American) Persimmon, all with edible fruits. At the symposium dedicated to his memory held in Oxford in 1996, the story was told of how the late Frank White, the authority on African Diospyros, asked at a stall in the Oxford market for some persimmons, but was firmly told, ‘Them’s Sharon Fruit’ – an indication of the success of the Israeli fruit-marketing machine in promoting this unappealing name. Whether known as Sharon Fruit, Kaki or Persimmon, the fruits of D. kaki are a beautiful sight in the Mediterranean, hanging from the leafless trees in autumn and into winter like Christmas baubles – reason enough for its cultivation to be practised more frequently further north. Numerous cultivars of it and of D. virginiana, whose fruit is similarly persistent (Sternberg 2004), have been selected for their culinary qualities.
A mysterious taxon widespread in cultivation is Diospyros wilsonii hort. This is grown in the Mediterranean (for example, at La Mortola, Italy, and at the Real Jardín Botánico in Madrid), and is praised for its delicious fruit (Zappa 2008). There is a tree against the nursery wall at Glasnevin, and it is growing well at the JC Raulston Arboretum, making a neat straight-trunked specimen with good dark leaves, 4 m tall when seen in 2006, from seed obtained from Jim Waddick in 1990. The taxon is not, however, mentioned by Flora of China or by Sargent (1916) in Plantae Wilsonianae, and its identity remains unclear, although it may be related to D. lotus. The name D. duclouxii Dode is also of somewhat uncertain application, but probably also refers to D. lotus. There are both male and female trees of D. duclouxii at the Hillier Gardens, reaching 8–10 m in 2007, looking very handsome with big glossy green leaves, and flowering well in June of that year.
In addition to the Asian species described here, several other Diospyros could possibly be worthy of attention in temperate horticulture. The South African D. austroafricana De Winter may be either a shrub or a small tree to 10 m, with densely hairy leaves and red berries (Coates Palgrave 1990). In the garden of Peter and Susan Grimshaw in Maidenhead, Berkshire a specimen originating from a Denver Botanic Garden collection in Eastern Cape Province has been fully hardy since 1997, although growing exceedingly slowly – now being a magnificent 60 cm tall. This is probably a high-altitude form of subsp. microphylla (Burch.) F. White. Diospyros austroafricana is available commercially in the United Kingdom and is grown in Californian gardens. The San Francisco Bay Area botanical gardens have several species of Diospyros not described here, as well as D. austroafricana. Others are D. lycioides Desf. and D. whyteana (Hiern) F. White from southern Africa, D. morrisiana Hance from Hong Kong, D. oldhamii Maxim. from Taiwan, and D. palmeri Eastw. from Mexico. Diospyros texana Scheele, a small multistemmed deciduous tree with white bark, is sometimes cultivated in the southeastern United States. Jan De Langhe (pers. comm. 2007) reports that he has seen a young specimen of Diospyros xiangguiensis S. Lee at Arboretum Hof ter Saksen Beveren, Belgium, and it seems probable that other Asian species will be hardy and worth trying. There is clearly much potential for exploration of this genus in temperate gardens. All species of Diospyros appreciate hot summers, and a site in full sun should be found for them.
Of this large and important genus (to which the ebony tree belongs) only three species are known to be really hardy in this country, although a fourth – D. kaki – will succeed in the warmer counties in the open, and in many places elsewhere against a wall. They are trees with alternate, entire leaves, and the shoots do not form terminal buds. The male and female flowers are on separate trees, and both are small and without beauty. The fruits are large, and beset at the base by the calyx, which continues to grow after the rest of the flower has fallen. These trees like a good loamy soil, and should be raised from seed, except the named varieties of D. kaki, which are grafted on seedlings.
The species cultivated in North America are reviewed by Dr Stephen Spongberg in Journal of the Arnold Arboretum, Vol. 58, pp. 147–60 (1977). See also his article in Arnoldia, Vol. 39, pp. 290–310 (1979).