thumb|Unripe carambolas on the tree
thumb|Carambola before pruning
thumb|Carambola after pruning
Carambola, also known as star fruit, is the fruit of Averrhoa carambola, a species of tree native to tropical Southeast Asia.
Carambola fruits contain oxalic acid and the neurotoxin caramboxin. Consuming large quantities of the fruit, especially for individuals with some types of kidney disease, can result in serious adverse health effects.
Origins and distribution
thumb|Sliced carambolas having 7, 6, and the usual 5 points
The center of diversity and the original range of Averrhoa carambola is tropical Southeast Asia, where it has been cultivated for centuries. It was introduced to the Indian subcontinent and Sri Lanka by Austronesian traders, along with ancient Austronesian cultigens like langsat, noni, and santol. They remain common in those areas and in East Asia and throughout Oceania and the Pacific Islands.
Like the closely related bilimbi, there are two main types of carambola: the small sour (or tart) type and the larger sweet type. The sour varieties have a higher oxalic acid content than the sweet type. Several cultivars have been developed in recent years. The most common cultivars grown commercially include the sweet types "Arkin" (Florida), "Yang Tao" (Taiwan), "Ma fueng" (Thailand), "Maha" (Malaysia), and "Demak" (Indonesia) and the sour types "Golden Star", "Newcomb", "Star King", and "Thayer" (all from Florida). Some sour varieties, like "Golden Star", can become sweet if allowed to ripen.
Ripe, sweet-type carambolas are sweet without being overwhelming, as they rarely have more than 4% sugar content. They have a tart, sour undertone. The taste is difficult to match, but it has been compared to a mix of apple, pear, grape, and citrus family fruits. Unripe star fruits are firmer and sour, and taste like green apples.
Ripe carambolas may also be used in cooking. In Southeast Asia, they are usually stewed in cloves and sugar, sometimes with apples. In China, they are cooked with fish. They may be cooked as a vegetable, pickled, or made into jams in Australia. In Jamaica, they are sometimes dried. In Thailand, they are cooked together with shrimp.
Health risks
Carambolas contain caramboxin and oxalic acid. Both substances are harmful to individuals suffering from kidney failure, kidney stones, or those under kidney dialysis treatment. Caramboxin is a neurotoxin which is structurally similar to phenylalanine, and is a glutamatergic agonist. These enzymes are significant in the first-pass elimination of many medications, and, thus, the consumption of carambola or its juice in combination with certain prescription medications can significantly increase their effective dosage within the body.
Cultivation
right|thumb|Unripe Indian carambola
thumb|Ripe carambola fruit with Indian spices
The carambola is a tropical and subtropical fruit which can be grown at elevations up to . It prefers full sun exposure, but requires enough humidity and annual rainfall of at least . for example, but fruiting also occurs at other times in some other locales, such as South Florida.
Major pests are carambola fruit flies, fruit moths, ants, and birds.
In the United States, commercial cultivation and broad consumer acceptance of the fruit only date to the 1970s, attributable to Morris Arkin, a backyard horticultuarlist, in Coral Gables, Florida. The 'Arkin' variety represented 98% of the acreage in South Florida in the early 21st century.
In popular culture
right|thumb|Carambola, photo taken in Assam
The trees are also grown as ornamentals for their abundant, brightly colored and unusually shaped fruits, as well as for their attractive dark green leaves and their lavender to pink flowers. in this setting known as "starfruit". They are one of the most valuable crops in the game. The in-game icon erroneously depicts the fruit as resembling its real-life cross-section, and the plant itself as a single-harvest crop instead of a tree.
The Filipino word for the starfruit, balimbing, due to its many-faced shape, has acquired the meaning in Philippine political discourse of a turncoat, someone who switches political allegiances not out of principle but for their own self-interest.