Langsat

The langsat tree grows 10 to 20 metres tall and produces long clusters of round to oval fruit with thin, pale buff to yellow skin that exudes a sticky white latex. Inside, the flesh is divided into five translucent white segments that taste sweet and sour, like a mix of grape and grapefruit. Some segments hold a green, bitter, flattened seed up to 2 centimetres long, while other segments are seedless. The seeds are very bitter, and eating them leaves a lasting unpleasant taste. Varieties include langsat, duku, which has thicker skin and sweeter flesh, and longkong. Fruit is sold fresh in markets, and seeds are used for planting.

Langsat comes from western Southeast Asia, with the Malay Peninsula, Sumatra, Borneo and southern Thailand considered the likely area of origin. It has been grown for centuries in villages across Malaysia, Indonesia, Thailand, the Philippines and beyond. The name langsat comes from the Malay language, while lanzones in the Philippines is a related form. The botanical name Lansium comes from the same root, and for a long time the species was called Lansium domesticum, though modern studies place it under parasiticum.

Langsat was widely cultivated in village orchards of the Malay world long before written records, valued as a seasonal fruit. Early European visitors, including Rumphius in seventeenth-century Ambon, described several forms. Regional varieties came to be known under separate names: duku in Malaysia and Indonesia, longkong in Thailand, and lanzones in the Philippines, where the town of Camiguin celebrates the fruit in a festival known as the Lanzones Festival each October.

Folk medicine across Southeast Asia has used parts of the tree, including the bark for dysentery and malaria, the fruit peel dried and burned as a mosquito-repelling incense, and the bitter seeds ground and used as a vermifuge or fever remedy. These practices are recorded in ethnobotanical surveys, but they have not been confirmed by clinical trials.

As a commercial crop, langsat has been limited by the fruit's short shelf life, since the skin browns within a few days after picking. Thailand developed the longkong as a specialised, thick-skinned type that travels better. Researchers have also studied the seeds and peel as sources of triterpenoids called lansiosides and onoceranoids.

Fresh fruit is peeled and eaten, with the seeds spat out, or the segments are preserved in syrup or made into jam and dessert. Fruit peel is dried and burned as a mosquito repellent in some villages. Seeds, being bitter, are not eaten as food but are used in traditional remedies, ground into pastes or steeped in water for fever, worms and diarrhoea, and the bark has similar uses. Wood from the tree is hard and used in construction and tool handles. Seeds are planted to raise new trees, though they quickly lose viability.

The edible flesh provides vitamin C, small amounts of calcium and potassium, and carbohydrates. Laboratory studies have found triterpenoids and phenolic compounds in seed and peel with antioxidant, anti-inflammatory and anti-malarial activity in vitro, but none of this has been proven in people. Seeds should not be seen as a medicine, and effective doses and safety are unknown. Traditional uses are best considered cultural information only.