Citrus decumana var. racemosa M. Roem; C. decumana var. patoniana Riccob.; C. maxima var. uvacarpa Merr. (sec. Swingle and Reece 1967)
Citrus x aurantium L., pro sp. [Grapefruit Group] (sensu Mabberley 1997, Bayer et al. 2009); Citrus paradisi Macfad. (sensu Swingle and Reece 1967; sensu Tanaka sec. Cottin 2002)
Swingle and Reece (1967) noted that:
"The grapefruit apparently originated in the West Indies. In spite of careful search, it has not been found native in the Old World, where the parent species is largely grown and where many horticultural varieties are known."
"Another alternative is that the grapefruit may be a hybrid of the pummelo with the sweet orange. The morphological characters of the twigs, leaves, flowers, fruits, and seeds would suggest this. The most important argument against such an origin of the grapefruit is the absence of any breakup of self-pollinated grapefruit seedlings into orange-like and pummelo-like forms. The fairly high fertility of the grapefruit when pollinated by Citrus reticulata 'Dancy' makes the absence of reversions in the self-pollinated seedlings of the grapefruit hard to explain. On the other hand, the hybrids of C. reticulata 'Dancy' with grapefruit show great variability; some of them are grapefruit-like and others somewhat orange-like. In view of this fact it seems best to retain the grapefruit, for the present at least, as an independent but satellite species immediately following C. grandis, with which it is so closely allied that many Citrus taxonomists consider it a variety of that species. Patrick Browne (1756, 1789) was perhaps the first to discuss the grapefruit, under the name "Forbidden Fruit" or "Smaller Shaddock." Lunan (1814, pp. 171-73) was the first to use the term grapefruit. He wrote: "There is a variety known by the name of Grapefruit, on account of its resemblance in flavor to the grape." Tanaka (1926) gave the taxonomic history of the grapefruit (in Japanese) and in the English summary a good technical description of its botanical characters."
"It must be admitted that the true nature of the grapefruit is still unknown. It is to be hoped that the mystery of its origin can be settled by some of the newer methods now used in taxonomic research."
Crown compact or dense, not weeping. First-year twig surface glabrous or pubescent; second- or third-year twig surface striate; thorns absent or not persistent or straight; prickles absent or not persistent. Petiole glabrous or pubescent, length short or medium; wings narrow, medium or wide, adjoining the blade or tucking beneath blade. Leaflets one, margin entire, crenate/crenulate or bluntly toothed, shade leaflet blades flat or weakly conduplicate, sun leaflet blades flat, weakly or strongly conduplicate. Scent of crushed leaflets sweetly orange-like, somewhat to strongly malodorous, or not scented. Fruit broader than long, as broad as long, or longer than broad; rind green-yellow (6), yellow (7-10), yellow-orange (11), or orange (12); rind texture smooth (1-3), slightly rough (4-5), or medium rough (6-7); firmness leathery; navel absent or present; flesh orange or yellow; taste grapefruit-like.
Hodgson (1967) provided the following additional notes on the species: "The common or ordinary grapefruit is increasingly referred to in the trade as the white grapefruit to distinguish it from the pigmented varieties. Typically, the trees are vigorous, large, and very productive and the fruit is seedy and rich in flavor. From the early seedling plantings in Florida, all of which trace back to the original introduction, numerous selections were made many years ago and named as varieties. The most important of these is Duncan, which was a seedling from a tree in the original planting. Many if not most of these early named varieties have proved to be indistinguishable and doubtless represent the same parental clone. In the markets of the United States, the fruit from seedling trees and some of these varieties, of which there remains considerable acreage, is usually sold under the name Florida Common."
Swingle and Reece (1967) provided the following additional notes on the species:
"A large, round-topped tree with dense foliage; twigs angular when young, glabrous or nearly so; leaves larger than those of the sweet orange, smaller than those of the pummelo, ovate, bluntly tipped and broadly rounded at the base, glabrous or nearly so; petioles rather broadly winged but not so broad as those of the pummelo, oblanceolate to obovate in shape, the somewhat broadly rounded tip touching the very broadly rounded base of the leaf blade; flowers large, borne singly or in small clusters in the axils of the leaves; calyx 5-lobed; petals smaller than those of the pummelo, often larger than those of the sweet orange; fruits larger than those of the sweet orange but smaller than those of most pummelos; seeds smaller than those of the pummelo, white, not yellowish, not ridged as are those of the pummelo."
"The fruit of the grapefruit contains a bitter glucoside, naringin, first discovered in the pummelo. According to Zoller (1918, p. 371), naringin is found in large quantities in the peel of the grapefruit (from 0.66 to 0.80 grams per 100 grams of fruit). It occurs without any hesperidin but seems able to give rise to a form of vitamin P, according to Szent-Györgyi (1938). It is different from the glycosides of hesperidin, found in the sweet orange, and aurantamarin, in the sour orange."
Bayer, R.J., D.J. Mabberley, C. Morton, C.H. Miller, I.K. Sharma, B.E. Pfeil, S. Rich, R. Hitchcock, and S. Sykes. 2009. A molecular phylogeny of the orange subfamily (Rutaceae: Aurantioideae) using nine cpDNA sequences. American Journal of Botany 96: 668–685.
Browne, P. 1756. The civil and natural history of Jamaica. Osborne, London. 503 pp.
Browne, P. 1789. The civil and natural history of Jamaica. Second edition. With four additional indexes. White & Son, London. 526 pp.
Cottin, R. 2002. Citrus of the World: A citrus directory. Version 2.0. France: SRA INRA-CIRAD.
Hodgson, R W. 1967. Horticultural varieties of Citrus. In: The Citrus industry. Ed. 2. Vol. I. W. Reuther, H. J. Webber, and L. D. Batchelor, eds. Riverside: University of California. http://lib.ucr.edu/agnic/webber/Vol1/Chapter4.html.
Lunan, J. 1814. Hortus Jamaicensis. St. Iago de la Vega Gazette, Jamaica. 2 vol.
Mabberley, D.J. 1997. A classification for edible Citrus (Rutaceae). Telopea 7: 167–172.
Swingle, W.T. and P.C. Reece. 1967. The botany of Citrus and its wild relatives. In: Reuther, W., H.J. Webber, and L.D. Batchelor (eds.). The Citrus industry. Ed. 2. Vol. I. University of California, Riverside. http://lib.ucr.edu/agnic/webber/Vol1/Chapter3.html.
Szent-Györgyi, A. 1938. Methoden zur Herstellung von Citron. Zeitschrift für physiologische Chemie. 255:126–31.
Tanaka, T. 1926. On the scientific name of the grapefruit. Bulteno scienca de la fakultato terkultura Kjusu imperia universitato. 2:67–83. [Japanese with English resume.]
Zoller, H. F. 1918. Some constituents of the American grapefruit (Citrus decamana ). Journal of Industrial and Engineering Chemistry 10:364–75.
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Citrus ID Edition 2
October, 2011
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