Longan

Dimocarpus longan, commonly known as the longan (Template:IPAc-en) and dragon's eye, is a tropical tree species that produces edible fruit.<ref name="Julia Morton">Template:Cite book</ref> It is one of the better-known tropical members of the soapberry family Sapindaceae, to which the lychee and rambutan also belong.<ref name="Julia Morton" /> The fruit of the longan is similar to that of the lychee, but is less aromatic in taste.<ref name="Fruiting pattern">Template:Cite journal</ref>

The longan (from Vietnamese long nhãn<ref name="Lour1790">Template:Cite book</ref> or Cantonese lùhng ngáahn {{#invoke:Lang|lang}}, literally 'dragon eye'), is so named because the black seed within the shelled fruit creates the appearance of an eyeball. The plant is native to tropical Asia and China.<ref>Template:GRIN</ref>

Description

Depending upon climate and soil type the tree may grow to over Template:Convert<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> in height, but it typically stands Template:Convert in height and the crown is round.<ref name="Julia Morton" /><ref name="Crane Balerdi">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> The trunk is Template:Convert thick<ref name="Julia Morton" /> with corky bark.<ref name="Crane Balerdi" /> The branches are long and thick, typically drooping.<ref name="Julia Morton" />

The leaves are oblong and blunt-tipped, usually Template:Convert long and Template:Convert wide.<ref name="Julia Morton" /> The leaves are pinnately compounded and alternate.<ref name="Crane Balerdi" /> There are 6 to 9 pairs of leaflets per leaf<ref name="Crane Balerdi" /> and the upper surface is wavy and a dark, glossy-green.<ref name="Julia Morton" />

The longan tree produces light-yellow inflorescences at the end of branches.<ref name="Julia Morton" /> The inflorescence is commonly called a panicle; they can be Template:Convert long, and widely branched.<ref name="Crane Balerdi" /> The small flowers have 5 to 6 sepals and brownish-yellow petals.<ref name="Crane Balerdi" /> The flower has a two-lobed pistil and 8 stamen. There are three flower types, distributed throughout the panicle;<ref name="Julia Morton" /> staminate (functionally male), pistillate (functionally female), and hermaphroditic flowers.<ref name="Crane Balerdi" /> Flowering occurs as a progression.<ref name="Crane Balerdi" />

The fruit are spherical and about Template:Convert wide; they hang in drooping clusters. The shell is tan, thin, and leathery with tiny hairs;<ref name="Crane Balerdi" /> when firm, it can be squeezed (as in the cracking of a sunflower seed) to shell the fruit.Template:Citation needed The flesh is translucent, and the seed is large and black with a circular white spot at the base.<ref name="Julia Morton" /><ref name="Crane Balerdi" /> This gives the illusion of an eye.<ref name="Julia Morton" /> The flesh has a musky, sweet taste, which can be compared to the flavor of lychee fruit.<ref name="Julia Morton" /> The seed is round, hard, and has a lacquered appearance.Template:Citation needed

The longan tree is somewhat sensitive to frost. While the species prefers temperatures that do not typically fall below Template:Convert, it can withstand brief temperature drops to about Template:Convert.<ref>Template:Cite book</ref> Longan trees prefer sandy soil with mild levels of acidity and organic matter.<ref name="Julia Morton" /> Longans usually bear fruit slightly later than lychees.<ref>Template:Cite journal</ref>

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Taxonomy

File:Longan seed.jpg

Seed

The longan is believed to originate from the mountain range between Myanmar and southern China. Other reported origins include Indonesia, India, Sri Lanka, upper Myanmar, north Thailand, Kampuchea (more commonly known as Cambodia), north Vietnam and New Guinea.<ref name="TK Lim">Template:Cite book</ref>

Its earliest record of existence draws back to the Han dynasty in 200 BCE. The emperor had demanded lychee and longan trees to be planted in his palace gardens in Shaanxi, but the plants failed. Four hundred years later, longan trees flourished in other parts of China like Fujian and Guangdong, where longan production soon became an industry.<ref name="BPU">Template:Cite book</ref>

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.<ref name="BPU" />

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 in the last 250 years.<ref name="BPU" /> The first European acknowledgment of the fruit was recorded by João de Loureiro, a Portuguese Jesuit botanist, in 1790. The first entry resides in his collection of works, Flora Cochinchinensis.<ref name="Lour1790" /><ref name="Fruiting pattern" />

Subspecies

Plants of the World Online lists:<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

• D. longan var. echinatus Leenhouts (Borneo, Philippines)
• D. longan var. longetiolatus Leenhouts (Viet Nam)
• D. longan subsp. malesianus Leenh. (widespread SE Asia)
• D. longan var. obtusus (Pierre) Leenh. (Indo-China)

Conservation

The wild longan population have been decimated considerably by large-scale logging 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.<ref name="IUCN" />

Diseases

Plant based diseases can affect both longan fruits and their trees, and the severity of these diseases can range from harmless cosmetic damage to rendering to the fruit inedible.

The most prevalent disease among longan plants is witch's broom, which can be found in all major longan-producing Asian territories, including China, Thailand, and Vietnam.<ref>Template:Cite journal</ref> Witch's broom deforms longan skin, and at times causes the plant to prematurely drop its fruit, similar to the Phytophthora palmivora.<ref>Template:Cite journal</ref>

Another common disease that longan trees can carry is the aptly named longan decline, which is largely prevalent in Thailand, with reports finding that it could affect up to 40% of longan trees alone.<ref name=":0">Template:Cite book</ref> Affected trees are more vulnerable to common tree pests and algae, and often bear low-quality fruit unworthy of yield.<ref name=":0" />

Algal spot is another plant disease that can affect longan plants and trees. Common among tropical fruits, the disease mainly takes form as red-orange algae that can appear on a fruit-bearing tree's leaves or branches.<ref>Template:Cite journal</ref>Algal spot on longan plants, like many other tropical fruits, is caused by Cephaleuros virescens.<ref>Template:Cite journal</ref>

An oomycete disease that causes blight on leaves and foliage of a plant and affects the related lychee, Phytophthora palmivora, can also appear on both longan plants and fruit,<ref name="Wang-et-al-20192">Template:Cite journal</ref> particularly in the Thailand region. When affecting longan, it can create brown spots on the fruit in an erratic fashion, and can also cause longan to drop prematurely from the plant. Early symptoms can also include a dark necrosis on the plant itself.<ref>Template:Cite journal</ref>

Stem-end rot is a disease common amongst litchi and longan, and causes browning and rot on the stem of the fruit. Longan also suffer from various decay-accelerating fungi.<ref name=":0" />

An oomycete disease that affects the related lychee, Phytophthora litchii, also afflicts D. longan.<ref name="Wang-et-al-20192" />

Cultivation

Currently, longan crops are grown in southern China, Taiwan, northern Thailand, Malaysia, Indonesia, Cambodia, Laos, Vietnam, India, Sri Lanka, the Philippines,<ref name="TK Lim" /> Bangladesh,<ref name="KhatunKarim2012">Template:Cite journal</ref> Mauritius, the United States, and Australia.<ref name="TK Lim" />

Growth

Longan, like its sister fruit lychee, thrives in humid areas or places with high rainfall, and can grow on most types of soil that does not induce issues with water drainage.<ref name=":1">Template:Cite book</ref> Ample temperatures are also instrumental in longan growth: while longan can resist small stretches of cool temperatures, they can be damaged or killed in longer stretches of temperatures as high as −2 degrees Celsius. Younger plants tend to be more vulnerable to the cold than those more mature.<ref name=":1" /><ref>Template:Cite book</ref>

Harvest

During harvest, pickers must climb ladders to carefully remove branches of fruit from longan trees. Longan fruit remain fresher if 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.<ref name="Muhammad Siddiq2">Template:Cite book</ref>

Fruit is picked early in the day to minimize water loss and to prevent high heat exposure, which would be damaging. The fruit is then placed into either plastic crates or bamboo baskets and taken to packaging houses, where the fruit undergo a series of checks for quality. 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 is split, under-ripe, or decaying is disposed of. The remaining healthy fruit is then prepared and shipped to markets.<ref name="BPU2">Template:Cite book</ref>

Many companies add preservatives to canned longan. Regulations control the preserving process. The only known preservative added to canned longan is sulfur dioxide, to prevent discoloration.<ref name="BPU2" /> 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, and efforts have been made to reduce this amount.<ref name="BPU2" />

Distribution

Longan is found commonly in most of Asia, primarily in mainland China, Taiwan, Vietnam and Thailand. China, the main longan-producing country in the world, produced about Template:Convert of longan in 2015–2017, accounting for 70% of the world's longan production and more than 50% of the world's longan plots.<ref>Luo, Jun, Can-fang Zhou, and Zhong Wan. "Analysis on the development status of lychee industry in Guangdong province in 2010." Guangdong Agric Sci 4 (2011): 16-8.</ref> Vietnam and Thailand produced around Template:Convert, respectively.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> 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.<ref name="BPU2" />

Yield

While longan yields average out to 2 to 5 tonnes per hectare, there have been observed yields of up to 19.5 tonnes per ha in Israel.<ref>Template:Citation</ref>

Advancements in selective breeding have allowed scientists to find a strain of longan containing a "high proportion of aborted seeds" at the end of a thirty-year breeding program in 2001.<ref>Template:Cite journal</ref> Studies in 2015 that aimed to aid longan breeding efforts discovered that −20 degrees Celsius is the optimal temperature for long-term storage of longan pollen, a key ingredient in enabling longan breeding programs.<ref>Template:Cite journal</ref>

Uses

Nutrition

Raw longan fruit is 83% water, 15% carbohydrates, 1% protein, and contains negligible fat (table). In a Template:Cvt reference amount, raw longan supplies 60 calories of food energy, 93% of the Daily Value (DV) of vitamin C, 11% DV of riboflavin, and no other micronutrients in appreciable quantities (table).

Culinary

The fruit is sweet, juicy, and succulent in superior agricultural varieties. The seed and the peel are not consumed. Apart from being eaten raw like other fruits, 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 has a drier sweetness similar to dates, lychees are often messily juicy with a more tropical, grape-like 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.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> In contrast with the fresh fruit, which is juicy and white, the flesh of dried longans is dark brown to almost black.

Once fermented, it can be made into longan wine.

See also

• Lansium parasiticum, the langsat or lanzones
• Talisia esculenta, a visually similar fruit from South America

External links

• Longan Production in Asia from the Food and Agriculture Organization of the United Nations