A. bilimbi is a commonly cultivated tree species of the Old World tropics introduced in the 1790s to the Neotropics, where it has since naturalized (Macfadyen, 1837; Morton, 1987). The species is also cultivated in western Africa (Burkill, 1985). It is listed in the Global Compendium of Weeds as a “naturalised, weed” (Randall, 2012) and is known to be invasive in the Old World tropics (Space et al., 2003). A risk assessment prepared for Hawaii gave the species a score of 1, indicating the need for further evaluation of its invasiveness (PIER, 2015).
Oxalidaceae, sometimes called the ‘wood sorrel’ family, includes over 800 species of herbs, shrubs, and trees, mostly of neotropical origin. Some taxonomists shifted Averrhoa from Oxalidaceae to a separate family, Averrhoaceae. However, this is not currently an accepted family and is treated as a synonym of Oxalidaceae (Ravindran, 2016). The genus name Averrhoa is in honour of the famous twelth-century philosopher Averrhoes from Cordoba, Spain (Macfadyen, 1837). The species name bilimbi derives from the Malay vernacular name for the species, a name still used in most tropical countries.
Averrhoa bilimbi L. and A. carambola L. are the only two species of commercial interest in the family, due to their fruits. The Indian (Hindi) name bilimbi has become the most popular vernacular name globally for A. bilimbi, but blimbe and cucumber tree are also used.
The following is taken from Morton (1987): “The tree is attractive, long-lived, reaches 16 to 33 ft (5-10 m) in height; has a short trunk soon dividing into a number of upright branches. The leaves, very similar to those of the Otaheite gooseberry and mainly clustered at the branch tips, are alternate, imparipirmate; 12 to 24 in (30-60 cm) long, with 11 to 37 alternate or subopposite leaflets, ovate or oblong, with rounded base and pointed tip; downy; medium-green on the upper surface, pale on the underside; 3/4 to 4 in (2-10 cm) long, 1/2 to 1 1/8 in (1.2-1.25 cm) wide. Small, fragrant, 5-petalled flowers, yellowish-green or purplish marked with dark-purple, are borne in small, hairy panicles emerging directly from the trunk and oldest, thickest branches and some twigs, as do the clusters of curious fruits. The bilimbi is ellipsoid, obovoid or nearly cylindrical, faintly 5-sided, 1 1/2 to 4 in (4-10 cm) long; capped by a thin, star-shaped calyx at the stem-end and tipped with 5 hair-like floral remnants at the apex. The fruit is crisp when unripe, turns from bright-green to yellowish-green, ivory or nearly white when ripe and falls to the ground. The outer skin is glossy, very thin, soft and tender, and the flesh green, jelly-like, juicy and extremely acid. There may be a few (perhaps 6 or 7) flattened, disc-like seeds about 1/4 in (6 mm) wide, smooth and brown.”
A. bilimbi is possibly native to tropical Southeast Asia, with the Moluccas suggested as a probable place of origin, and is widely cultivated in the New World Tropics and the west tropical African region (Burkill, 1985; Morton, 1987; Orwa et al., 2009; Acevedo-Rodriguez and Strong, 2012). It is cultivated throughout Indonesia and Philippines where the plants are found in semi-wild conditions everywhere. It is a very common backyard plant in Sri Lanka, India and Myanmar, and is grown widely in Malaysia, Thailand and in most other tropical countries. In 1793, bilimbi was carried from the island of Timor to Jamaica and, after some years, was planted in Cuba, Puerto Rico, Trinidad, the lowlands of Central America, Venezuela, Colombia, Ecuador, Surinam, Guyana and Brazil and even in northern Argentina, where it is very popular among Asiatic residents as it is in Hawaii. In the USA it is also grown as an occasional curiosity in southern Florida (Ravindran, 2016).
The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.
A. bilimbi, like A. carambola, is generally considered to have originated in tropical Southeast Asia but some authors have speculated it to originate in the Neotropics, which has led to some uncertainty over the native status of the species in some Asian countries. In the Philippines, for example, both Merrill (1904) and Quisumbing (1951) report both A. bilimbi and A. carambola as having been introduced via the galleon trade to the Philippines from tropical America during the Spanish colonial period. A. bilimbi is reported as either an introduction to India (Orwa et al., 2009) or possibly native (Bircher and Bircher, 2000), and is reportedly native to China (Flora of China Editorial Committee, 2015). Today, the species is well known and widely cultivated in tropical Asia, particularly the Philippines, for its food and medicinal uses. It was introduced into Queensland, Australia, at the end of the nineteenth century, and has been grown commercially in the region since that time (Morton, 1987)
In 1793 the species was introduced into Jamaica by way of, as Macfadyen (1837) writes, “His Majesty’s ship Providence”. From there, it was eventually distributed across the West Indies and Central America, into northern South America (Morton, 1987). It is unclear how prevalent the species was in the West Indies during the nineteenth century, as it was not included in Bello’s (1881; 1883) work on Puerto Rico. Neither was it included in Britton’s (1918) work on Bermuda, but by 1903 it had been identified as an economic plant in Puerto Rico (Cook and Collins, 1903), and was also included in Britton and Wilson’s (1924) flora of Puerto Rico and the Virgin Islands. The species was not included in Sesse and Mocino’s Flora Mexicana (1894) but is now known to occur there (Flora Mesoamericana, 2015).
Risk of introduction for this species needs further evaluation, according to a PIER risk assessment of the species prepared for Hawaii (PIER, 2015). Although in Singapore the species is considered a casual introduction, as plants “do not form self-replacing populations and rely on repeated introductions or limited asexual reproduction for persistence” (Chong et al., 2009), it is reported to be invasive in Palau (Space et al., 2003), weedy in Asia Pacific and Central Africa (Randall, 2012), and “freely escaping” in China (Flora of China Editorial Committee, 2015). Invasive traits include repeated history of introduction to non-native habitats, vigorous growth, and dispersal by water and birds (Morton, 1987; Orwa et al., 2009; Flora of China Editorial Committee, 2015).
A. bilimbi is widely grown in gardens and cultivated areas of tropical regions around the world. It is also known to occur in undisturbed places, near villages and in secondary forest in Papua New Guinea and throughout settled areas of the Philippines, where it is both cultivated and semi-cultivated (Merrill, 1923; PIER, 2015). In China and Taiwan, the species is widely cultivated and freely escaping along rivers and in areas of secondary vegetation (Flora of China Editorial Committee, 2015). The species occurs in the canal zone of Panama (Panama Checklist, 2014). It is also a common cultivated species in gardens “across the plains of India” (Morton, 1987).
The heterostylus self-incompatibility (SI) system is a feature of both A. bilimbi and A. carambola. Members of these species have various style lengths such that the stigmas in each morph more or less correspond to the positions of the anthers in the other morphs; this requires multiple morphs of the species, and ensures that trees are not inbred (Knight, 1965; Ganders, 1979; Wong et al., 1994). A. carambola is distylous, with two morphs, and A. bilimbi is tristylous, with three morphs, so when cultivating either species all morphs should be planted to ensure fruit yield (Ganders, 1979; Staples and Herbst, 2005).
Flower panicles have 18–64 flowers that form on the trunk and older branches. Flowers take about a week from bud burst to open flower, with flowers opening in the morning. It takes about 15 days for the whole panicle to flower. Fruit set occurs 15–20 days after inflorescence emergence and is indicated by petal fall with the stigma persisting on the end of the fruit. (Paull and Duarte, 2012). Due to profuse flower production in each tree, pollination effectively becomes intra-tree and not inter-tree. Flowering continues throughout the year and fruit is available for most of the year, but usually there are one or two pronounced harvest seasons, each lasting about two months. Fruit development takes about 90-110 days (Ravindran, 2016).
BothA. bilimbiandA. carambolathrive in tropical regions and prefer a climate with evenly distributed rainfall and a 2-3 month dry season, but can tolerate frost-free subtropics and wetter climates, although not the wettest zones of Malaysia (Morton, 1987; Samson, 1991; FAO EcoCrop, 2015). BothAverrhoaspecies should be grown in well-drained soils between pH of 5.5-6.5 and grow well on peat (Samson, 1991);A. bilimbican grow in sand or limestone (Morton, 1987), and can tolerate an absolute pH range of 5.5-8.3 (FAO EcoCrop, 2015).A. bilimbicannot tolerate long spells of cold weather, flooding, or salinity, and its growth is stunted by shade (Morton, 1987; Samson, 1991; Bircher and Bircher, 2000). The species generally grows at low elevations up to 500 m in Java (Samson, 1991) and to 1000 m in Mesoamerica (Flora Mesoamericana, 2014; Panama Checklist, 2014).
The seed of A. bilimbi are likely dispersed by water, as the species is known to escape freely from cultivation along riverbanks (Flora of China Editorial Committee, 2015).
Vector Transmission (Biotic)
Seeds might be carried or eaten by animals who feed on the fleshy fruit encapsulating the seeds, although this is somewhat unlikely as the fruit is extremely acidic. Its fruit have, however, been reportedly eaten by birds (Saad et al., 2011).
Little information is available regarding its potential accidental introduction as a contaminant, but considering its seeds are relatively large this is not likely to be a main pathway of dispersal.
The species has been intentionally introduced in tropical regions around the world for human cultivation, as it is used in food and medicine.
Outside of cultivation, increased populations of A. bilimbi could positively impact livelihoods of communities, particularly those who rely on local foraging and can harvest fruits of this species for food and sale.
A. bilimbi is cultivated primarily for its juicy but very sour edible fruit and for use in traditional medicine. The fruit is used in the preparation of jams and jellies and for cooling beverages. In such cases fruits are pricked or cut into small pieces and steeped in water overnight for reducing sourness and for bringing down the oxalic acid level. Fruits, after acidity reduction, are used in various preparations, involving both fish and vegetables. In Pakistan, for example, the fruit is often preserved in sugar and sometimes pickled (Flora of Pakistan, 2015), and in Malaya the fruits are processed and made into dried sliced snacks (Hanelt et al., 2001). In Philippine cuisine the fruits are widely used to add a tart or acid flavour, much like how lemon juice and tamarinds are used (Staples and Herbst, 2005). Although the fruit is generally regarded as too acid for eating raw, Morton (1987) reports that the green, raw fruits are used to make a relish which is served with rice and beans in Costa Rica, and that ripe fruits are frequently added to curries in the Far East. In Costa Rica the species is used both as flavouring and a preservative (Burger, 1991). A. bilimbi is made into chutneys and is used in place of raw mango and tamarind. Flowers are also collected, washed, air dried and preserved in sugar syrup (Ravindran, 2016).
In the Philippines fruits are eaten raw, curried or added as a souring agent for traditional Filipino dishes; often the fruit is made into a stock for use in various dishes that need sourness. In Indonesia it is also preserved after sun drying, the product being often known as asam sunti. For its preparation bilimbi fruits are sliced thinly, salted and dried in the sun for many days. Dried bilimbi is a popular ingredient in the cookery of Sumatra, especially in the Aceh region that is located in the northern tip of the island. In Kerala (India) it is made into a relishing pickle, while in Karnataka, Goa and in many other places the fruits are eaten raw together with salt and spices. In rural areas of southern India and Sri Lanka, the commonest use of bilimbi fruit is in the preparation of fish curries for which this sour spice gives a peculiar flavour and taste. Bilimbi is widely used in the Seychelles, imparting a unique taste to many local fish preparations. In Hawaii, chefs use juiced fruit as a substitute for vinegar in salad dressings and soups. It is also dried and reconstituted with other juices and spices for use in sauces.
As a commercial food crop, A. bilimbi requires special handling; fruits must be handpicked, because of the thin skin, and cannot be stored for more than a few days (Morton, 1987).
The leaves, flowers, and fruits of this species have medicinal uses within various cultures. In Pakistan, the fruit is used as an astringent and, when cooked, is eaten to cure piles and scurvy (Flora of Pakistan, 2015). In the Philippines its leaf paste is applied as a poultice on itches, swellings, mumps and rheumatism and in other types of skin eruption. In other Asian traditions, juice from the fruit is used in a concoction for fevers, a paste can be made from the leaves and applied tropically to cure mumps, rheumatism, and pimples, or brewed to treat syphilis, and an infusion of the flowers is used to treat coughs and thrush (Quisumbing, 1951). In Malaysia, leaves, either fresh or after fermentation, are used to treat venereal diseases. Infusion of leaves is given for coughs and it is taken as a tonic by women after child birth. Infusion of flowers in boiling water is prescribed as an effective remedy for coughs and thrush. In Java, bilimbi fruit mixed with black pepper is prescribed for ailments caused by weather changes and a paste of bilimbi and pepper is smeared over the body for reducing fever. Fruit preserved in sugar is indicated for coughs, beriberi and biliousness. Fruit syrup is used as a cure for fever and inflammation, and to stop bleeding from the rectum and alleviating internal haemorrhoids. In many countries leaf paste is used as an antidote for poisonous animals. Further ethnobotanical information for this species can be found in Duke’s (2015) Phytochemical and Ethnobotanical Databases.
Most other uses relate to the fruit’s high acidic content, such as cleaning blades, as mordants in the preparation of an orange dye for silk fabrics, and for cleaning cloth and metal (Morton, 1987; Staples and Herbst, 2005). It is widely used as a stain remover throughout South East and Far East countries because of its high oxalic acid content (Ravindran, 2016). Its wood can also be used as fuel, a purple dye from the petals is used as an indicator in chemistry, and the species has potential in agroforestry (FAO EcoCrop, 2015).
Bilimbi fruit juice and water extract (but not alcohol or hexane extracts) exhibit notable anti-hypercholesterolaemic and hypoglycaemic activities. An active compound was isolated from the fraction that showed optimum activity at a dose level of 0.3 mg/kg; however, the compound remains uncharacterized. The effective dose is indicated as: fruit (125 mg/kg) and the aqueous extract (50 mg/kg); it was effective in reducing lipids in rats fed a high-fat diet. Some studies have also indicated a significant hypoglycaemic effect for bilimbi leaves. In addition, bilimbi leaves also possess hypotriglyceridaemic, anti-lipid peroxidative and anti-atherogenic properties in animal systems. The ethanol extract of bilimbi was shown to elevate significantly serum HDL cholesterol concentration by 60% compared with a standard control. The extract significantly enhanced the anti-atherogenic index and HDL/total cholesterol ratio but did not affect LDL-cholesterol and total cholesterol.
Bilimbi fruit juice has been shown to possess high bacteriostatic and bactericidal properties, and washing fresh shrimps in bilimbi fruit juice was shown to inhibit bacterial growth very significantly during preservation. Chloroform and methanol extracts of fruit were shown to be active against bacteria.
Little information is available regarding methods of prevention and control as the species has not yet been reported to a priority weed species. Considering its invasive risk assessment score of 1 (requires further evaluation) (PIER, 2015) as well as the short shelf life of its seeds, this need for research is not yet urgent but may be required in the near future.
Forzza RC, Leitman PM, Costa AF, Carvalho Jr AA et al, 2012. List of species of the Flora of Brazil. (Lista de espécies Flora do Brasil)., Rio de Janeiro, Brazil: Rio de Janeiro Botanic Garden. http://floradobrasil.jbrj.gov.br/2012/