Overview
Lychee (Litchi chinensis Sonn.) is one of the most important members of the Sapindaceae family that has over 2,000 species and 150 genera. Related fruit from Asia include longan (Euphoria longan), rambutan (Nephelium lappaceum) and pulasan (Nephelium mutabile). Rambutan and pulasan are similar to lychee with red or yellow skin; however, long hairs or spinterns replace the protuberances. Rambutan and pulasan are strictly tropical, while lychee and longan crop best in the warm sub-tropics or at elevation in the tropics. The Litchi genus contains two other non-commercial sub-species from the Region. Lychee is a long-lived, evergreen tree that produces its new leaves, flowers and fruit on terminal shoots. The inflorescences produce many hundreds of functionally male and female flowers that carry from 5 to 80 attractive fruit at harvest. The red-skinned fruit contain a single seed, surrounded by a juicy sweet aromatic aril or flesh. Cultivars with large fruit, small seeds and a distinctive flavour are sought after in the market-place.
The Sapindaceae or soapberry family contains more than 2,000 species from 150 genera, mostly trees and shrubs, but rarely herbs, widely distributed throughout the warm sub-tropics and tropics. The majority of species are native to Asia, although there are a few in South America, Africa and Australia. New species are still being described. The most specialized growth forms are the rather strange unbranched palm-like trees such as Talisia and woody climbers like Sejania and Paullinia. The largest trees including Schleschesa oleasa and Pometia pinnata (tuan, dawa or Fiji longan) may reach up to 60 m in height.
Several genera include useful ornamentals: Sapindus saponaria, a small tree up to 10 m high in Florida, the West Indies and South America; Koelreuteria paniculata (golden rain tree), a round-headed species up to 10 m high in China, the Republic of Korea and Japan; Xanthoceras sorbifolia, bunge, a small tree up to 5 m high in northern China planted for its attractive flowers; and Ungnadia speciosa (Mexican buckeye), a shrub and Cardiospermum halicacabum (balloon-vine), an annual vine planted in southern USA.
Many other members of the Sapindaceae are important timber trees, nuts, or sources of beverages, oils or drugs. Saponins are present in the fruits, seeds and other tissues of several species. Some types such as Sapindus saponaria are used as soap substitutes in the tropics. Schleichera trijuga is the source of macassar oil used in ointments. Paullinia cupana is a vine from South America, the source of guarana, much drunk in Brazil and elsewhere. Blighia sapida, akee is a fruit from West Africa, with an edible aril, but poisonous if not eaten at the correct stage of ripeness. The mamoncillo or Spanish lime, Melicocca bijuga is also grown for its fruit in South America. Pometia pinnata is sometimes grown in Papua New Guinea and the Pacific for its edible aril.
Other minor species worthy of evaluation for their fruit include: Cubilia bancoi, kubili from low to medium elevations in the Philippines; Diploglottis cunninghamii, native tamarind from sub-tropical Australia; Talisia olivaeformis, talisia from tropical America; Alectryon macrococcus, mahoe from Hawaii; and Chrysanthus macrobotrys, ndgulu from Central Africa.
The most important members of the Sapindaceae are the attractive, eye-catching fruit of the sub-family Nepheleae from the orient. Lychee (Litchi chinensis), longan (Euphoria longan), rambutan (Nephelium lappaceum) and pulasan (Nephelium mutabile) are similar trees, but differ in fruit morphology and ecology. Lychee is the most economically significant member of the group.
Lychee is regarded as one of the kings of tropical fruit and has a very long history in Asia. Fruit are very attractive, with bright red skin covered by angular or conical protuberances. Longan resembles lychee, but the fruit are smaller, smoother, yellow-tan to brown, milder in flavour and less acid. About a third of people in Asia prefer longan to lychee, whereas in Australia, America and Europe, lychee is more popular. Canned longans are more acceptable than canned lychees.
Rambutan and pulasan are similar to lychee, with red or yellow skin, however, long hairs or spinterns replace the protuberances. Rambutan and pulasan are strictly tropical, cropping only in warm, wet, lowland areas, whereas lychee and longan are found in the warm sub-tropics or above 500 m in the tropics.
The Sapindaceae were originally described by Cambessedes in 1828. However, the first detailed systematic study was not published until 1890. Radlkofer based his classification on a wide range of evidence, including the presence or absence of a terminal leaflet, the number of ovules per carpel, the structure of the fruit, presence or absence of an aril, and pollen morphology.
There have been several revisions of the Sapindaceae, but the scheme of Radlkofer's is essentially accepted, with only minor modification. According to plant characteristics, pollen morphology and geography, the Sapindaceae are split into two sub-families - Dodonaeoideae (Austral distribution) and Sapindoideae. The latter can be separated into three main groups, centered around Sapindeae (pantropical), or Cupanieae (pantropical), and a third group separating into Thiouinieae and Paullinieae, both predominantly American.
Members of the Sapindaceae share several characteristics. The leaves are normally alternate, mostly pinately or palmately, sometimes single compound. Flowers are usually unisexual, borne in racemes, panides or corymbs. There are usually four to five free, sometimes fused sepals and four to five petals (often with hairs), which may be absent, and a well-marked disc between the petals and stamens. There are eight to ten stamens in two whorls. The filaments are free and often hairy. The ovary is superior with two to four lobes, and the style simple or divided. The fruit include capsules, nuts, berries, drupes, samaras or schizocarps, often red, containing seeds. They lack endosperm, with the embryo folded or curved.
The Litchi genus contains two other forms that have not been commercialized. Sub-species philippinensis is found in the Philippines (Luzon, Sibuyan, Samar and Mindanao) and Papua New Guinea at high elevation, while sub-species javensis is recorded in the Malay Peninsular and Indonesia. The Philippines lychee has long, oval-shaped fruit with long, thorn-like protuberances. Fruit split in the middle when ripe, displaying an inedible aril that only partly covers the seed. Sub-species javensis is a rare specimen found in Chinese gardens in West Java and Indo-China and has fruit similar to cultivated lychee, but with a thinner aril. It is reported to flower and fruit regularly in the tropics. Many of the Malayan specimens belong to sub-species chinensis.
There are seven species in the genus Euphoria, all from tropical and sub-tropical Asia, but longan is the only one significantly grown for its edible fruit. E. didyma (alpay) has small (2 cm diameter) round, green warty fruit with shell-like rind, big seed and a thin, juicy, sweet, edible aril. The tree is native to the Philippines and is widely distributed in both wet and dry areas. E. malaiense (mata kuching) produces fruit of similar size to the alpay and longan. Fruit have a tough skin that is pale dull yellow with dark raised specks. The aril which envelops a big seed is whitish, translucent and sweet, and in good forms nearly 0.5 cm thick, although usually much thinner. Trees grow wild in Malaysia, Borneo, Sumatra and the Celebes.
Rambutan and pulasan are thought to be native to west Malaysia and Sumatra, although trees that have escaped from cultivation blur the original distribution. They are close relatives of lychee, and equally desirable fruit, but are not as well known. Fruit are very similar to each other and are often confused. Pulasan has smaller fruit, narrower leaflets, a more open tree and fewer fruit in a cluster. The fruit skin is thicker and the spinterns or tubercles shorter. Trees are also reported to be less productive than rambutan. Other species with the edible arils grown in Asia include N. eriopetalum (lotong), N. glabrum (redan), N. philippense (bulala) and N. excrospermoides (aluao).
Lychee is a long-lived, evergreen tree up to 30 m tall in old specimens, with a short stocky trunk. In some cultivars, the branches are crooked or twisting and spreading forming a crown broader than high, while in other cultivars, the branches are fairly straight and upright forming a compact, rounded crown.
The leaves are alternative and compound, with two to five leaflets. The leaflets are oblong and 5 to 15 cm long. The new flushes are a distinctive red-brown when immature and light to dark green as they mature. The inflorescences are many branched panicles, each with one or more leaves and up to 3,000 flowers, and from 5 to 80 fruit at harvest (Figure 1).
The flowers are small, yellowish-white, functionally male or female and apetalous. Functionally male flowers have six to ten stamens. There are usually two stages of male flowering overlapping with the female cycle: a true male flower first and then a functionally male flower that opens towards the end of the flowering period. The second male flower has a rudimentary bicarpellate pistil. This is absent in the first stage. Functionally female flowers have six to ten staminodes and a functional, bicarpellate pistil (Figure 2). The last stage of male flowering generally supplies most of the pollen used to fertilize the female flowers.
Figure 1. Panicle, flowers and fruit cluster.
Figure 2. Flower types (
,
and ).
Fruit are highly variable, depending on the cultivar (Figure 3). They can be round, ovoid or heart-shaped, and from 2.0 to 3.5 cm in diameter. The skin can be smooth or rough with distinct protuberances, thick or thin, and pink-red, bright red or purple-red. The flesh or aril is an outgrowth of the outer cells of the seed coat (outer integument), and in good cultivars may comprise 80 percent of fruit weight. The aril is generally translucent white, juicy or firm, and sweet and aromatic in better cultivars. Many cultivars can be distinguished by their flavour and aroma. The fruit contain a single dark brown seed 6 to 12 mm wide and 10 to 23 mm long. Some cultivars have a high proportion of aborted seeds and thus a high flesh recovery. They are popular in the market-place, especially in Asia. There are a few cultivars that produce nearly seedless fruit, although the fruit usually weigh less than 10 g.
Figure 3. Fruit characteristics.
The composition of the fruit determined from studies in Australia was (per 100 g fresh weight): moisture, 81 percent; protein, 1.1 g; fat, 0.1 g; carbohydrate, 18 g; Ca, 2 mg; Fe, 0.5 mg; thiamin, 0.05 mg; riboflavin, 0.07 mg; niacin, 0.5 mg; and ascorbic acid, 49 mg. The total soluble sugar content was 18 percent or higher.
Bibliography
Chapman, K. R. 1984. Lychee, Litchi chinensis Sonn.. In Tropical Tree Fruits For Australia (P. E. Page, Editor). Queensland Department of Primary Industries, Brisbane pp. 179-91.
Heywood, V. H. 1978. Flowering Plants of the World. Oxford University Press, London 335 pp.
Leenhouts, P. W. 1971. A revision of Dimocarpus (Sapindaceae). Blumea 19, 113-31.
Leenhouts, P. W. 1978. Systematic notes on the Sapindaceae-Nephelieae. Blumea 24, 395-403.
Leenhouts, P. W. 1986. A taxonomic revision of Nephelium (Sapindaceae). Blumea 31, 373-436.
Menzel, C. M. 1991. Litchi. In Plant Resources of South-East Asia Vol. 2. Edible Fruit and Nuts (E. W. M. Verheij and R. E. Coronel, Editors). Pudoc, Wageningen, The Netherlands pp. 191-5.
Yap, S. K. 1983. Amesiodendron and Litchi (Sapindaceae). Garden Bulletin of Singapore 36, 19-24.
Yeap, C. K. 1987. The Sapindaceous fruits and nuts. Yearbook of the West Australian Nut and Tree Crops Association 12, 16-33.
