An orange—specifically, the sweet orange—is the citrus fruit Citrus sinensis (syn. Citrus aurantium L. var. dulcis L., or Citrus aurantium Risso) and its fruit. The orange is a hybrid of ancient cultivated origin, possibly between pomelo (Citrus maxima) and tangerine (Citrus reticulata). It is a small flowering tree growing to about 10 m tall with evergreen leaves, which are arranged alternately, of ovate shape with crenulate margins and 4–10 cm long. The orange fruit is a hesperidium, a type of berry.

Oranges originated in Southeast Asia. The fruit of Citrus sinensis is called sweet orange to distinguish it from Citrus aurantium, the bitter orange. In a number of languages, it is known as a "Chinese apple" (e.g. Dutch Sinaasappel, "China's apple", or "Apfelsine" in German). The name is thought to ultimately derive from the Dravidian word for the orange tree, with its final form developing after passing through numerous intermediate languages.

Fruit

All citrus trees are of the single genus Citrus, and remain largely interbreedable; that is, there is only one "superspecies" which includes grapefruits, lemons, limes and oranges. Nevertheless, names have been given to the various members of the genus, oranges often being referred to as Citrus sinensis and Citrus aurantium. Fruits of all members of the genus Citrus are considered berries because they have many seeds, are fleshy and soft, and derive from a single ovary. An orange seed is called a pip. The white thread-like material, attached to the inside of the peel is called pith.

Persian orange

The Persian orange, grown widely in southern Europe after its introduction to Italy in the 11th century, was bitter. Sweet oranges brought to Europe in the 15th century from India by Portuguese traders, quickly displaced the bitter, and are now the most common variety of orange cultivated. The sweet orange will grow to different sizes and colours according to local conditions, most commonly with ten carpels, or segments, inside.

Some South East European tongues name orange after Portugal, which was formerly the main source of imports of sweet oranges. Examples are Bulgarian portokal 1, Greek portokali 2, Romanian portocală and Georgian phortokhali 3. Also in South Italian dialects (Neapolitan), orange is named portogallo or purtualle, literally "the Portuguese ones". Related names can also be found in non-European languages: Turkish Portakal, Arabic al-burtuqal 4, Persian porteghal 5 and Amharic birtukan.