OriginNative to the rainforests of Sabah, Sarawak, Borneo, Sumatra and Celebes. It is one of four native varieties of longan.
DescriptionIsaus, related to longans, look like mini custard apples. Bumpy green exterior with translucent flesh encasing a deep red-black seed.
Growth HabitatTropical and subtropical areas.
FoliageLeaves are 9.9-22cm long by 2.7-10cm wide, medium green in colour. Young leaf flushes are deep red in colour.
FlowersFlowers are yellow brown with densely hairy petals with smooth sepals or outer smaller petal coverings, each with 6-10 stamens.
FruitsThe fruit is about 25cm across with green pebbly skin at maturity ripening yellowish-green. The seed is similar to that of the longan (D. longana), measuring slightly less than half the fruit diameter 11mm. The skin of Isau is thicker than that of longan. The fruit is also sweeter and drier.
Harvest The whole panicle of Longan fruits with one or two leaves is cut with a knife or scissors. Removal of too much leaves and wood with the fruit panicles at harvest reduces flowering in the next season.
SoilIsaus grow well in a rich sandy loam and also on moderately acid, somewhat organic, sand. 
PruningPrune to increase sunlight and air circulation. Prune for structural and formative growth. Prune also for maintenance and production.
FertilizationIn China, fertilizers are applied to fruit bearing Longan trees at a frequency of five to six times a year. Application of fertilizer at N:P:K ratios of 1:0.5:1 or 1:1:4 has been reported to increase yield significantly.
PropagationVegetative propagation was divided into two techniques, namely conventional and in vitro techniques. In vitro technique is preferred than conventional techniques because it is often the only practical way to produce large amounts of true-to-type isau plants.
1 Longan has 2.5g of water, 1.8 calories, 0.5g carbohydrates, 2.5g of Vit C, 0.3 mg of Magnesium, 0.6mg of phosphorus, 8.0gm of potassium.
Health BenefitsThere is not much information on Isau but the closest relative Longan has these benefits –

The fruit contains a range of vitamins and minerals that include iron, magnesium, phosphorus and potassium as well as vitamins A and C.

With a high vitamin C content, the fruit is helpful in protecting the body from colds and flu, and helps to boost the immune system. Vitamin C helps the body in absorbing iron and it plays a part in maintaining healthy skin and enabling the body to heal wounds. Vitamin C helps in improving wound healing and increases longevity as it fights the free radicals that damage cells.

Together with polyphenols, it helps in fighting off free radicals that are damaging to cells and cause cancer and damage to arteries thus increase the risk for heart attacks and strokes. Studies are ongoing regarding the effectiveness and safety of antioxidants in the longan.

The fruit is low in fats and calories and makes a healthy addition to the diet of those wanting to lose weight. Longans contain complex carbohydrates (sucrose) and glucose that increases energy improves stamina and reduces hunger.

Logans are recommended as anti-depressants as they have a relaxing effect on the nervous system, they enhance nerve function, lower irritability and reduce fatigue. All of this is due to the essential minerals contained in the fruit.

They are said to contain iron that is required in red blood cell formation and therefore helps reduce the risk of anaemia.

The vitamins contained in the fruit help in enhancing complexion of skin, minimises the cracking and peeling of skin as well as helping in keeping the teeth and gums in good health. It also has a positive impact on vision and is helpful in reducing cataract formation and reducing the risk of age related macular degeneration and night blindness.

The seed of the fruit is administered as it helps counteract heavy sweating and the pulverised kernel is said to contain Saponins, tannin and fats that serve a styptic or a substance that draws tissue together thereby constricting the tissue and effectively stopping blood and other secretions.

Longans are also used to treat insomnia, to overcome anxiety and a difficulty in concentration as it contains fitokimianya that serves to relax the nerves and provides a calming effect.
Commercial UsesLongan can be frozen, canned or dried. The dried, longan aril is black, leathery and smoky in flavour and is used mainly to prepare a refreshing drink. This drink is very popular among the Chinese. A liqueur is made by macerating the longan flesh in alcohol. Dried longan flesh is also an ingredient in herbal medicine used for stomach ache, insomnia and as an antidote for poison. The seed is used as a shampoo, like soapberries (Sapindus saponaria L.), due to its saponin content. Dried leaves, which contain quercetin and quercitrin, and flowers of longan are also sold as ingredients in Chinese herbal medicine.
Food SuggestionFresh Isau with Red Date Drink

Ingredients (serves 1, prep time 8 mins ):
- 6 dried longan
- 3 red dates (Jujube), removed the seeds
- 10ml honey (to taste)
- 500ml (2 cup) hot water

Put fresh isau or logan and red dates into a glass and pour in 1 cup of hot water (>=85°C).
Rinse the ingredients and drain. Then Pour in another 1 cup of hot water. Cover for 5 minutes. Serve


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