Averrhoa bilimbi aka Bilimbi

Averrhoa bilimbi is an evergreen fruit tree in the Oxalidaceae family. Its common names include bilimbi, camias, and cucumber tree. Kew places its native range in central and eastern Malesia. Useful Tropical Plants gives a narrower range in Indonesia’s Moluccas. It grows in lowland forests, often beside rivers. People grow it in gardens across the tropics. Commercial planting is less widespread than home growing.

This long-lived tree grows slowly and has a low, open crown. It can also take the form of a shrub. Most plants reach about 7–10 feet (2–3 m) tall. Some reach 49 feet (15 m), well above that usual range. The trunk is short and can span about 1 foot (0.3 m) across. Its evergreen form gives it a lasting place in tropical gardens. Its main garden value lies in its useful fruit.

The fruit turns greenish yellow and has flesh that lets light through. Its shape is round in cross-section or has five slight angles. Each fruit holds a few flat seeds without a fleshy covering. Ripe fruit is crisp, juicy, and very sour. Some people eat thin slices in salads or with salt. More often, cooks use it to add sharpness to dishes. It goes into curries, sauces, chutneys, pickles, and sweets. The fruit also supplies vitamin C. The sour flowers can be made into preserves.

Bilimbi suits the warm, damp climate of the tropical lowlands. It grows best with daytime temperatures of 23–30°C. The cited range it can endure is 10–36°C. Even light frost can harm it. Young growth suffers severe damage at about −1°C. Temperatures of −3°C or lower can kill mature plants. The tree grows well where rain falls through the year. It prefers annual rainfall of 1,200–2,300 mm. Yet it can also cope with a dry season lasting two or three months.

The plant has uses beyond food. Its sour juice helps remove stains from cloth and brass. People also use the fruit when dyeing silk. The petals yield a purple dye used as a chemical indicator. The wood serves as fuel but rarely reaches useful timber sizes. Leaves, flowers, and fruit have roles in traditional medicine. Those uses do not establish that the remedies work. Useful Tropical Plants lists no known hazards. That statement does not amount to a full safety assessment.