containing many juice-filled vesicles and usually a few seeds (pips). When unripe, the fruit is green. The grainy irregular rind of the ripe fruit can range from bright orange to yellow-orange, but frequently retains green patches or, under warm climate conditions, remains entirely green. Like all other citrus fruits, the sweet orange is non-climacteric. The Citrus sinensis group is subdivided into four classes with distinct characteristics: common oranges, blood or pigmented oranges, navel oranges, and acidless oranges. Other citrus groups also known as oranges are: Bergamot orange (Citrus bergamia Risso), grown mainly in Italy for its peel, producing a primary essence for perfumes, also used to flavor Earl Grey tea. It is a hybrid of bitter orange x lemon. Bitter orange (Citrus aurantium), also known as Seville orange, sour orange (especially when used as rootstock for a sweet orange tree), bigarade orange and marmalade orange. Like the sweet orange, it is a pomelo x mandarin hybrid, but arose from a distinct hybridization event. Mandarin orange (Citrus reticulata) is an original species of citrus, and is a progenitor of the common orange. Trifoliate orange (Poncirus trifoliata), sometimes included in the genus (classified as Citrus trifoliata). It often serves as a rootstock for sweet orange trees and other Citrus cultivars. An enormous number of cultivars have, like the sweet orange, a mix of pomelo and mandarin ancestry. Some cultivars are mandarin-pomelo hybrids, bred from the same parents as the sweet orange (e.g. the tangor and ponkan tangerine). Other cultivars are sweet orange x mandarin hybrids (e.g. clementines). Mandarin traits generally include being smaller and oblate, easier to peel, and less acidic. Pomelo traits include a thick white albedo (rind pith, mesocarp) that is more closely attached to the segments. Orange trees generally are grafted. The bottom of the tree, including the roots and trunk, is called rootstock, while the fruit-bearing top has two different names: budwood (when referring to the process of grafting) and scion (when mentioning the variety of orange). Etymology The word ultimately derives from Proto-Dravidian or Tamil (). From there the word entered Sanskrit ( or ), meaning 'orange tree'. The Sanskrit word reached European languages through Persian () and its Arabic derivative (). The word entered Late Middle English in the 14th century via Old French (in the phrase ). The French word, in turn, comes from Old Provençal , based on the Arabic word. In several languages,