Longan

Plants of the World Online[5] lists:

• 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)

Depending upon climate and soil type the tree may grow to over 100 feet (30 m)[6] in height, but it typically stands 30–40 ft (9–12 m) in height[7] and the crown is round.[8] The trunk is 2.5 ft (0.8 m) thick[7] with corky bark.[8] The branches are long and thick, typically drooping.[7]

The leaves are oblong and blunt-tipped, usually 4–8 inches (10–20 cm) long and 2 in (5 cm) wide.[7] The leaves are pinnately compounded and alternate.[8] There are 6 to 9 pairs of leaflets per leaf[8] and the upper surface is wavy and a dark, glossy-green.[7]

The Longan tree produces light-yellow inflorescences at the end of branches.[7] The inflorescence is commonly called a panicle and are 4–18 in (10–46 cm) long, and widely branched.[8] The small flowers have 5 to 6 sepals and petals that are brownish-yellow.[8] The flower has a two-lobed pistil and 8 stamen. There are three flower types, distributed throughout the panicle;[7] staminate (functionally male), pistillate (functionally female), and hermaphroditic flowers.[8] Flowering occurs as a progression.[8]

Longan fruit with flesh, seed, and peel visible.

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.[8] The flesh is translucent, and the seed is large and black with a circular white spot at the base.[7][8] This gives the illusion of an eye.[7] The flesh has a musky, sweet taste, which can be compared to the flavor of lychee fruit.[7]

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).[9] Longans usually bear fruit slightly later than lychees.[10]

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.[1]

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.[11]

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. Four hundred years later, longan trees flourished in other parts of China like Fujian and Guangdong, where longan production soon became an industry.[12]

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.[12]

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.[12] 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.[3]

The longan was described in Joao de Loureiro's work, Flora Cochinchinensis, published in 1790.

Currently, longan crops are grown in southern China, Taiwan, northern Thailand, Malaysia, Indonesia, Cambodia, Laos, Vietnam, India, Sri Lanka, Philippines, Australia, the United States, and Mauritius.[11] It is also grown in Bangladesh.[13]

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 have 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.[14] In contrast with the fresh fruit, which is juicy and white, the flesh of dried longans is dark brown to almost black.

Longans, raw

A peeled longan fruit
Nutritional value per 100 g (3.5 oz)
Energy	251 kJ (60 kcal)
Carbohydrates	15.14 g
Sugars	n/a
Dietary fiber	1.1 g
Fat	0.1 g
Protein	1.31 g
Threonine	0.034 g
Isoleucine	0.026 g
Leucine	0.054 g
Lysine	0.046 g
Methionine	0.013 g
Phenylalanine	0.030 g
Tyrosine	0.025 g
Valine	0.058 g
Arginine	0.035 g
Histidine	0.012 g
Alanine	0.157 g
Aspartic acid	0.126 g
Glutamic acid	0.209 g
Glycine	0.042 g
Proline	0.042 g
Serine	0.048 g
Vitamins	Quantity %DV†
Thiamine (B1)	3% 0.031 mg
Riboflavin (B2)	12% 0.14 mg
Niacin (B3)	2% 0.3 mg
Vitamin C	101% 84 mg
Minerals	Quantity %DV†
Calcium	0% 1 mg
Iron	1% 0.13 mg
Magnesium	3% 10 mg
Manganese	2% 0.052 mg
Phosphorus	3% 21 mg
Potassium	6% 266 mg
Sodium	0% 0 mg
Zinc	1% 0.05 mg
Link to USDA Database entry Vitamin B6/Folate values were unavailable
Units μg = micrograms • mg = milligrams IU = International units
†Percentages are roughly approximated using US recommendations for adults. Source: USDA FoodData Central

Longan is commonly found in traditional Eastern folk medicine. This is a common occurrence since, prior to the 1800s, longan was most prevalent in Asia.[12]

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.[15]

It is found commonly in most of Asia, primarily in mainland China, Taiwan, Vietnam and Thailand.[16] China, the main longan-producing country in the world, produced about 1,900 thousand tonnes of longan in 2015–2017. Vietnam and Thailand produced around 500 thousand and 980 thousand tonnes, respectively.[17] 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.[12]

The longan industry is very new in North America and Australia. Commercial crops have only been around for twenty years. In the United States, longan is grown in Florida, Texas, Nevada, Georgia, California, Hawaii, and Arizona. They are also grown in Australia, along the eastern coast.

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.[18]

Fruit is picked early in the day in order 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 prepped and shipped to markets.[12]

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.[12] 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.[12]

Potassium chlorate has been found to cause the longan tree to blossom. However, this stresses the tree if used excessively, and eventually kills it.

Wikimedia Commons has media related to Dimocarpus longan.

Wikispecies has information related to Dimocarpus longan.

• Fruits of Warm Climates: Longan
• Longan Production in Asia from the Food and Agriculture Organization of the United Nations