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Description: The sour orange, Citrus aurantium, is an erect tree that ranges in height from less than 10 ft (~3 m) to about 30 ft (~9 m) and has a more compact crown than the sweet orange (Citrus sinensis). C. aurantium produces smooth, brown bark and green twigs that are angular when young, and flexible, with thorns that range in length from 2.5-8 cm (~1-3 in) long but not very sharp. The fragrant evergreen, compound leaves with minutely toothed edges are about 6-14 cm (~2.5-5.5 in) long and about 4-10 cm (1.5-4 in) wide; they are usually ovate in shape with a short point at the apex and alternately arranged on broad-winged petioles that are considerably longer than those of the sweet orange. In addition, the leaves of C. aurantium are dark-green above, pale beneath, and dotted with tiny oil glands. The bisexual flowers are highly fragrant and are borne at the axils. They are solitary or clustered and about 3.75 cm (1.5 in) wide with five white, slender, separated petals surrounding a mass of up to more than 20 yellow stamens. The useful fruit is round, oblate or oblong-oval and about 5-10 cm (~2.5-5 in) wide. C. aurantium has a rough surface and a relatively thick, aromatic but bitter peel with minute, sunken oil glands. The peel becomes bright reddish-orange when mature, and the10-12 segments of the acidic, pulpy fruit contain a few to numerous seeds. Because the center of the fruit becomes hollow when mature, the sour orange fruit is “able to float” (Stone 1970).
Distribution: The sour orange, C. aurantium, is probably indigenous to southeastern Asia and is generally assumed to have been a relatively early post-European-contact introduction into the Pacific Islands, although natives of some tropical South Pacific Islands, especially Fiji, Samoa, and Guam, believe the tree was brought to their homelands in pre-European-contact times. On the other hand, because the fruit becomes hollow when mature and therefore can float, this species of Citrus might have dispersed to some islands without human help?
Uses by Island or Island Group: A species of multiple uses, the sour orange, C. aurantium, is generally used to make beverages and to flavor food. It is fruit sold as a minor cash crop in some countries, and parts of the tree are used medicinally (e.g., see Clarke and Thaman 1993). More specifically, the juice, peel, and essential oil of the sour orange have all been used in traditional therapy for “digestive problems, epilepsy, fatigue, insomnia, infections, respiratory problems, skin problems, and many other uses,” and the essence of bitter orange as a flavoring is added in some liquors such as Triple Sec and Cointreau. Although the fruit and skins of sour orange are sometimes used to make marmalade in several places around the world, they are not used for this purpose in the tropical Pacific islands, except in New Caledonia. On the other hand, sour orange trees are sometimes cultivated in rural and home gardens throughout most of Polynesia and in some areas of Micronesia and Melanesia. Where it is cultivated on Pacific Islands, including some in Micronesia, the crushed fruit and macerated leaves of sour orange trees are used to make a lather in water which is used as soap for washing clothes and shampooing the hair.
Uses in Yap: According to Falanruw et al. (1987:7), the sour range, C. aurantium, is one of many cultivated tree species “commonly found in the agroforest overstory” of Yap.
Usesin the Mariana Islands: Stafford (1905) referred tocommon use of “wild orange” in the Mariana Islands that he called the “soap orange” and which may refer to Citrus aurantium(var. saponacea Safford), or perhaps to (or also to) the “wild orange” species Citrus macroptera Montrouzier?According to Safford (1905:226):
“The wild orange of Guam is identical with the ‘moli’ of Fiji and Samoa, and, as in those island groups, it is apparently indigenous or of prehistoric introduction. It is not edible. The saponaceous fruit is used by the natives of Guam not only for washing the hair, as in several other Pacific islands, but also as a substitute for soap in washing clothing. [Historically on the island of Guam it was] a common sight to see scores of women and girls standing waist deep in the river with an oblong shallow wooden tray (batea) before them either afloat or resting on a rock. On this tray the linen is spread, rubbed with orange pulp, and vigorously scrubbed with a corncob. Often the entire surface of the rivers where the current is sluggish is covered with decaying oranges.”
Stone (1970:354), referring to Safford, indicated the macerated pulp and leaves of C. macroptera (“wild orange”) has been utilized in hair and clothes washing, and suggested that this species is seemingly “but not certainly, wild and native in Guam,” and is not rare, “at least in certain areas, such as Barrigada Hill.” Referring specifically to C. aurantium, Moore and McMakin (1979:171) indicated that the fruit of sour orange species has been used on Guam “for cooking, making sauces and for orangeade.” Among the botanical reports of its occurrence (wild or cultivated?) in the Mariana Islands include, for example, Ryozo Kanehira (1931:288) who described C. aurantium growing in “thickets at medium altitudes” on Saipan where he collected specimens; and Fosberg et al. (1977:30) noted the presence of C. aurantium in an “area of former habitation, below 100 m” on the southern coast of Asuncion Island (also see Raulerson 2006; http://www.hear.org/pier/species/citrus_aurantium.htm).
Uses on Namoluk Atoll: According to Marshall (1975:37), the sour orange trees, C. aurantium, known as Kurukur on Namoluk, are cultivated and grow spontaneously in partially shaded areas on the atoll islets away from the beaches:
“The extremely sour oranges are eaten or squeezed for their juice to which sugar is added. Fragrant roots are used in leis, the tough wood sometimes is used for coconut husking stakes, and long, straight branches formerly were very important as staves in stick dancing and warfare (these staves, like the plant, were called ‘kurukur’). The bark is used in medicines.”
Uses in Chuuk: The pounded roots of a citrus species (possibly C. aurantium)known locally in Chuuk as Kurukur or Kurukuri, are mixed with the leaves, bark, and fruit of other plants to make a perfumed precipitate (called soonen ayis) for scenting necklaces and headbands, as well as human hair and body (Merlin and Juvik 1996).
Uses in Pohnpei: According toBalick et al. (2009:491), Citrus aurantiumreportedly is used medicinally in Pohnpei to treat high fever(soumwahu en rerrer) “when the oahs palm leaf (Metroxylon amicarum) is not available, the skin [of C. aurantium] is peeled off, squeezed on a cloth, and put into the mouth three times daily.”