Dimocarpus longan, commonly known as the longan (UK: //; US: //, //), is a tropical tree that produces edible fruit. It is one of the better-known tropical members of the soapberry family (Sapindaceae), to which the lychee also belongs. Included in the soapberry family are the lychee, rambutan, guarana, korlan, pitomba, Spanish lime and ackee. Longan is commonly associated with lychee, which is similar in structure but more aromatic in taste. It is native to Southern Asia.
The longan (from Cantonese lùhng-ngáahn 龍眼, literally "dragon eye"), is so named because it resembles an eyeball when its fruit is shelled (the black seed shows through the translucent flesh like a pupil/iris). The seed is small, round and hard, and of an enamel-like, lacquered black. The fully ripened, freshly harvested fruit has a bark-like shell, thin, and firm, making the fruit easy to peel by squeezing the pulp out as if one is "cracking" a sunflower seed. When the shell has more moisture content and is more tender, the fruit becomes less convenient to shell. The tenderness of the shell varies due to either premature harvest, variety, weather conditions, or transport/storage conditions.
Depending upon climate and soil type the tree may grow to over 100 feet (30 m) in height, but it typically stands 30–40 ft (9–12 m) in height and the crown is round. The trunk is 2.5 ft (0.8 m) thick with corky bark. The branches are long and thick, typically drooping.
The leaves are oblong and blunt-tipped, usually 4–8 inches (10–20 cm) long and 2 in (5 cm) wide. The leaves are pinnately compounded and alternate. There are 6 to 9 pairs of leaflets per leaf and the upper surface is wavy and a dark, glossy-green.
The Longan tree produces light-yellow inflorescences located at the end of branches. The inflorescence is commonly called a panicle and are 4–18 in (10–46 cm) long, and widely branched. The small flowers have 5 to 6 sepals and petals that are brownish-yellow. The flower has a two-lobed pistil and 8 stamen. There are three flower types, distributed throughout the panicle; staminate (functionally male), pistillate (functionally female), and hermaphroditic flowers. Flowering occurs as a progression.
The fruit hangs in drooping clusters that are circular and about 1 in (2.5 cm) wide. The peel is tan, thin, and leathery with tiny hairs. The flesh is translucent, and the seed is large and black with a circular white spot at the base. This gives the illusion of an eye. The flesh has a musky, sweet taste, which can be compared to the flavor of lychee fruit.
The Longan tree is somewhat sensitive to frost. Longan trees prefer sandy soil. While the species prefers temperatures that do not typically fall below 4.5 °C (40 °F), it can withstand brief temperature drops to about −2 °C (28 °F). Longans usually bear fruit slightly later than lychees.
The wild longan population have been decimated considerably by large-scale loggings in the past, and the species used to be listed as Vulnerable on the IUCN Red List. If left alone, longan tree stumps will resprout and the listing was upgraded to Near Threatened in 1998. Recent field data are inadequate for a contemporary IUCN assessment.
The longan is believed to originate from the mountain range between Myanmar and southern China. Other reported origins include India, Sri Lanka, upper Myanmar, north Thailand, Kampuchea (more commonly known as Cambodia), north Vietnam and New Guinea.
Its earliest record of existence draws back to the Han Dynasty in 200 BC. The emperor had demanded lychee and longan trees to be planted in his palace gardens in Shaanxi, but the plants failed. Fortunately, four hundred years later, longan trees flourished in other parts of China like Fujian and Guangdong, where longan production soon became an industry.
Later on, due to immigration and the growing demand for nostalgic foods, the longan tree was officially introduced to Australia in the mid-1800s, Thailand in the late-1800s, and Hawaii and Florida in the 1900s. The warm, sandy-soiled conditions allowed for the easy growth of longan trees. This jump-started the longan industry in these locations.
Despite its long success in China, the longan is considered to be a relatively new fruit to the world. It has only been acknowledged outside of China recently in the last 250 years. The first European acknowledgement of the fruit was recorded by Joao de Loureiro, a Jesuit botanist, in 1790. The first entry resides in his collection of works, Flora Cochinchinensis.
The fruit is sweet, juicy and succulent in superior agricultural varieties. The seed and the shell are not consumed. Apart from being eaten fresh and raw, longan fruit is also often used in Asian soups, snacks, desserts, and sweet-and-sour foods, either fresh or dried, and sometimes preserved and canned in syrup. The taste is different from lychees; while longan have a drier sweetness, lychees are often messily juicy with a more tropical, sour sweetness.
Dried longan are often used in Chinese cuisine and Chinese sweet dessert soups. In Chinese food therapy and herbal medicine, it is believed to have an effect on relaxation. In contrast with the fresh fruit, which is juicy and white, the flesh of dried longans is dark brown to almost black.
A peeled longan fruit
|Nutritional value per 100 g (3.5 oz)|
|Energy||251 kJ (60 kcal)|
|Dietary fiber||1.1 g|
|Aspartic acid||0.126 g|
|Glutamic acid||0.209 g|
Link to USDA Database entry
Vitamin B6/Folate values were unavailable
|Percentages are roughly approximated using US recommendations for adults.
Source: USDA Nutrient Database
Longan is commonly found in traditional Eastern folk medicine. This is not an unusual occurrence since, prior to the 1800s, longan was most prevalent in Asia.
In ancient Vietnamese medicine, the "eye" of the longan seed is pressed against snakebites to absorb the venom. This was ineffective, but is still commonly used today.
It is found commonly in most of Asia, primarily in China, Taiwan, Vietnam and Thailand. China, the main longan-producing country in the world, produced about 1,300 million tonnes of longan in 2010. Vietnam and Thailand had produced around 600 million and 500 million tonnes, respectively. Like Vietnam, Thailand's economy relies heavily on the cultivation and shipments of longan as well as lychee. This increase in the production of longan reflects recent interest in exotic fruits in other parts of the world. However, the majority of the demand comes from Asian communities in North America, Europe and Australia.
The longan industry is very new in North America and Australia. Commercial crops have only been around for twenty years. In Florida, the small quantity produced are sold only at local farmer's markets. In Australia, the crops are much bigger, stretching along the northern and eastern coasts. The weather is much better suited for longan growth.
During harvest, pickers must climb ladders to carefully remove branches of fruit from longan trees. It has been found that longan fruit remain fresher when still attached to the branch, so efforts are made to prevent the fruit from detaching too early. Mechanical picking would damage the delicate skin of the fruit, so the preferred method is to harvest by hand. Knives and scissors are the most commonly used tools.
It is also encouraged to pick the fruit earlier in the day in order to "minimize water loss" as well as prevent high heat exposure, which would be damaging. The fruit is then carefully placed into either plastic crates or bamboo baskets and taken to packaging houses, where the fruit undergo a series of checks for standards. The packaging houses are well-ventilated and shaded to prevent further decay. The process of checking and sorting are performed by workers instead of machinery. Any fruit that are split, under ripe, or decaying are disposed of. The remaining healthy fruit are then prepped and shipped to markets.
In terms of distribution, many companies add preservatives and chemicals to canned longan. These chemicals have been popularly known to, though not yet officially proven, cause unpleasant sensations such as burning lips, tingling of the mouth and tongue, and poor digestion. Due to these discoveries, more regulations have been made to control the preserving process. So far, the only known chemical added to canned longan is sulfur dioxide to prevent discoloration. There have been no studies to ascertain whether it has harmful effects on consumers.
Use of chemicals is not limited only to canned longan. Fresh longan that is shipped worldwide is exposed to sulfur fumigation. Tests have shown that sulfur residues remain on the fruit skin, branches, and leaves for a few weeks. This violates many countries' limits on fumigation residue, but efforts have been made to reduce this amount.
Potassium chlorate has been found to cause the longan tree to blossom. However, this causes stress on the tree if it is used excessively, and eventually kills it.