None
Citrus L. (sec. Mabberley 2004, Bayer et al. 2009); Fortunella Swingle (sec. Swingle and Reece 1967; Cottin 2002)
Swingle and Reece (1967) noted that:
"The kumquat orange, though described by early Chinese writers on agriculture, remained virtually unknown to Europeans until recent times. The kumquat is mentioned in many early Chinese works and described in some detail by Han Yen-chih (1923) in his treatise on the oranges written in 1178. Later works of both Chinese and Japanese authors treat of it fully, often with fairly good illustrations.
The first vague description of the kumquat orange in European literature was published by Ferrari in 1646 in his Hesperides and was based on reports made to him by Alvaro Semedo, a Portuguese Jesuit who lived for twenty-two years in China. Ferrari's successors, Sterbeeck, Volckamer, Risso and Poiteau, and other authors of monumental illustrated works on citrus fruits, have added nothing to our knowledge of the kumquat.
Full descriptions of the round and oval kumquats were published by Hume (1903, 1909), but not until 1912 was there a good account of these plants published in Europe, when Trabut (1912) described them and distinguished them from the so-called "chinosis" or "chinotto" (Citrus aurantium var. myrtifolia), with which they had been confused by Volckamer (1708) and many subsequent European writers. Two years later, Trabut (1914) published in Algeria a fuller illustrated account of these plants and gave an explanation of the failure of the kumquat to become known and be propagated in continental Europe, namely, that seedlings do not thrive and, furthermore, that viable seed is hard to secure; moreover, he stated that the kumquat, when grafted on sour or Seville oranges (the stock generally used), did not succeed at all."
Crown compact or dense, not weeping. First-year twig surface glabrous; second- or third-year twig surface striate; thorns absent or not persistent or straight; prickles absent or not persistent or straight. Petiole glabrous, length short or medium; wings absent or, if present, narrow, adjoining the blade. Leaflets one, margin entire, crenate/crenulate or bluntly toothed, shade leaflet blades flat or weakly or strongly conduplicate. Sun leaflet blades weakly or strongly conduplicate. Scent of crushed leaflets spicy or peppery, freshly lemon-like, somewhat to strongly malodorous, or not scented. Fruit broader than long, as broad as long, or longer than broad; rind variegated, green-yellow (6), yellow (7-10), yellow-orange (11), orange (12), or red-orange (13); rind texture smooth (1-3), slightly rough (4-5), or medium rough (6-7); firmness leathery; navel absent; flesh orange or yellow; taste acidic-sweet or sour.
Swingle and Reece (1967) provided the following additional notes on the genus:
"Shrubs or small trees; young branches angular, the older ones rounded; spines borne singly at one side of the bud in the axils of the leaves, or wanting; leaves 1-foliolate, rather thick, blunt-pointed or even retuse, acute or rounded at the base, veins evident above, scarcely showing beneath, lower surface pale green, densely glandular-dotted; petioles narrowly winged or merely margined, sometimes not articulated with the leaf blade; flowers borne singly or in few-flowered clusters in the axils of the leaves, hermaphrodite, 5-merous (rarely 3-, 4-, or 6-merous); flower buds, 8-10 mm long, more or less angular in cross-section; petals 5 (rarely 4 or 6), white, acute, 8-12 mm long; stamens 16 or 20, polyadelphous, cohering irregularly in bundles; filaments broad, but tapering at the tip; pistil seated on a well-marked cylindrical disk; ovary subglobose, with 3-7 locules, with 2 collateral ovules in each locule; ovary merging gradually or abruptly into the short style, this usually shorter than the ovary, sometimes shorter than the stigma; stigma capitate, symmetrical, cavernous within because of the large, deep-seated oil glands (1/4-1/5 the diam. of the stigma); fruits small, usually 2-4 times as long as the petiole, ovoid or globose; peel rather thick, fleshy, aromatic, and sweet flavored, containing large immersed oil glands; segments 3-7; pulp-vesicles small, fusiform or subglobose, stalked, containing an acid juice; seeds ovate in outline, smooth; embryo pistache green, germination with hypogeous cotyledons; first foliage leaves broadly ovate, subsessile, opposite as in Citrus.
The genus Fortunella resembles Citrus in the general appearance of the stems, twigs, spines, leaves, flowers, and fruits and in having the polyadelphous stamens cohering in bundles and normally four times as numerous as the petals. It differs from Citrus: (1) in having an isomerous or hypomerous ovary normally with three to five, rarely six or seven, locules (not polymerous with 8 to 15 or more locules); (2) in having two collateral ovules in each locule (not 4 to 12); (3) in having a cavernous stigma containing a few large, deeply immersed, lysigenous oil glands, usually in pairs, oval in cross section, with the radial diameter longer, about one-fourth to one-fifth the diameter of the stigma (in Citrus the homologous oil glands are so much smaller [one-tenth to one-fifteenth the diameter of the stigma in C. sinensis] that they do not give a cavernous character to the stigma); (4) in having the under surface of the leaves pale green, nearly veinless, and with very numerous, small, deep-green glandular dots; (5) in having very small fruits with acid pulp and a sweet, edible, more or less pulpy skin; (6) in having small, more or less angular flower buds.
The kumquat bears abundant orange- or flame-to-orange-colored fruits of small size, often less than an inch in diameter. Fortunella margarita and F. japonica , widely cultivated in China and Japan and in all subtropical regions, have fruits with a relatively thick, fleshy, sweet, edible peel, with four to seven segments filled with mildly acid pulp. A third species, with long, slender leaves and long petioles, F. polyandra , commonly cultivated in the Malay Peninsula, has larger globose fruits with a thin peel. A fourth species, F. hindsii, which grows wild in the mountains of southern China and on the island of Hong Kong, has very small globose fruits with three to four segments."
"One of the kumquats, F. polyandra, is native to tropical regions; the other three grow in cool subtropical or even warm temperate regions. The type species of Fortunella, F. margarita, and the closely related F. japonica not only are resistant to cold when in a dormant condition but also exhibit the highest degree of winter dormancy of any of the True Citrus Fruit Trees. These two species of kumquats can endure fairly warm weather in winter or early spring lasting for many days or even for some weeks without starting new growth (Swingle, 1910, 1913; Swingle and Robinson 1923, p. 229.)
Fortunella approaches Atalantia, and differs strikingly from Citrus, in having only two collateral ovules near the top of each locule (Citrus has 4 to 12 ovules). However, Fortunella differs from Atalantia in having four times as many stamens as petals (instead of twice as many) and agrees with Citrus in having similar twig, leaf, spine, flower, and fruit characters. The leaves, however, show very many more oil glands on the underside than are present in any species of Citrus, often ten times as many. In many superficial fruit characters Fortunella agrees with the Australian desert lime, Eremocitrus glauca. The seeds are very different, however, and the stem, twig, leaf, and flower characters are so strikingly different that it is not possible to regard these genera as being very closely related."
Kumquats and kumquat hybrids
For diagnostic purposes, cultivars in this group can be divided into three classes based on fruit size. As fruit size varies to some extent on an individual plant, it is necessary to gauge the approximate average size when attempting to place a cultivar into one of the three classes. Within the size classes, cultivars can be differentiated to some extent by leaf scent, color of the fruit flesh, and subtle differences in leaf dimensions.
Small-fruited cultivars (fruits usually < 1.5 cm long). This group includes the procimequats and some calamondins. The two can be distinguished by the scent of the crushed young leaves. Calamondins have a distinctive, bready doughy scent, whereas procimequats do not. Procimequats also generally bear smaller fruits (0.7 to 1.2 [1.3] cm long). Fruits of calamondins vary from 1.5 to 3 cm long. Fruits of both cultivars are generally as broad as long or broader than long. Leaf blades also vary in general dimension. Procimequats tend to exhibit narrow elliptical leaves with bases and apices often tapered to about the same degree (and thus exhibiting a rather symmetrical shape). Calamondin leaves tend to have a higher length to width ratio, with leaves frequently at least half as wide as long.
Medium-fruited cultivars (fruits usually 1.5 to 3.5 cm long). This group includes calamondin, Crassifolia, Meiwa, and Nagami (among others). Fruits in this group tend to be distinctly longer than broad. Calamondin can be distinguished from all others in the group by the distinctive bread doughy scent of the crushed young leaves. Meiwa plants grown in the UCR Citrus Variety Collection are distinctive in that they generally do not exhibit a petiole wing articulation. The blade is thus extends uninterrupted to the petiole base. A few leaves on a given plant may exhibit incomplete articulation, but the vast majority show no articulation at all. This condition appears to be unique to Meiwa, at least in Riverside, and is not shared by any other kumquat or kumquat hybrid seen in the course of this developing this tool. Fruits of Meiwas are about 1.4-2.4 (-2.7) cm long and the flesh is the orange one might associate with a mandarin (from here on “mandarin-orange”). Aside from the articulation, Meiwa is difficult to distinguish from plants known as Crassifolia. Crassifolia fruits are about 1.8-2.5 cm long and exhibit a mandarin-orange colored flesh. Nagami can be distinguished from both Meiwa and Crassifolia in that its fruits generally have a higher length to width ratio. Nagami fruits usually fall in the range of 2.2-3.5 cm long with flesh that is also mandarin-orange colored.
Large-fruited cultivars (fruits usually 3 to 6 cm long). As in the medium-fruited group above, fruits in the large-fruited group tend to be distinctly longer than broad. This group includes the citrangequats, mandarinquats, and orangequats. The scent of crushed young leaves can be helpful in recognizing plants in one of these three hybrid categories. Citrangequats tend to be either somewhat malodorous or exhibit a scent similar to Trifoliate Orange. Mandarinquats tend to exhibit a scent reminiscent of mandarins. Orangequat tend to exhibit a sweetish scent, reminiscent of sweet oranges. Flesh color can also be useful diagnostically. Citrangequats tend to exhibit fruit flesh of a similar color as Trifoliate Orange, in contrast to the mandarinquats and orangequats which tend to exhibit a mandarin-orange colored flesh.
Citrangequats. Sinton and Thomasville can be distinguished from one another in part by subtle differences in leaf blade size and length to width ratio. Sinton tends to exhibit leaves shorter (ca. 4-6 cm long) and broader relative to their overall length (slightly less than half as long as wide). Sinton also tends to bear somewhat shorter fruits (ca. 3-4.5 cm long). Thomasville in contrast tends to exhibit leaves longer (ca. 5.5-8.5 cm long) and narrower relative to their overall length (width about 40% of the length). Thomasville fruits tend to be in the range of 4-5 (-6) cm long.
Mandarinquats. Indio exhibits some of the largest leaves among kumquat hybrids (ca. 7-9 x 3-3.5 cm). Its young leaves when crushed exhibit a typical mandarin scent. Its fruits are mandarin-orange colored and about 4-6 cm long.
Orangequats. Nippon exhibits leaves in the range of 4.5-5.5 (-7) cm long. Leaves tend to be between 33 and 37% as wide as long. The crushed young leaves are reminiscent of sweet orange. Fruits fall within the range of 3.5-4.5 cm long.
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.
Cottin, R. 2002. Citrus of the World: A citrus directory. Version 2.0. France: SRA INRA-CIRAD.
Han, Y.-c. 1923. Han Yen-chih's Chü lu (written 1178). Monograph on the oranges of Wenchou, Chekiang. Translated by Michael J. Hagerty, with introduction by Paul Pelliot. T'oung Pao, Leiden, Ser. 2, 22: 63–96.
Hume, H.H. 1903. The kumquats. Florida Agricultural Experimental Station Bulletin 65: 550–566.
Hume, H.H. 1909. Citrus fruits and their culture. Orange Judd & Co., New York. 587 pp.
Mabberley, D.J. 2004. Citrus (Rutaceae): A review of recent advances in etymology, systematics and medical applications. Blumea 49: 481–498.
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.
Swingle, W.T. 1910. New types of citrus fruits for Florida. Proceedings of the Florida State Horticultural Society 23: 36–41.
Swingle, W.T. 1913. New citrous fruits. American Breeders Magazine 4: 83–95.
Swingle, W.T. and T.R. Robinson. 1923. Two important new types of citrous hybrids for the home garden, citrangequats and limequats. Journal of Agricultural Research. 23: 229–238.
Trabut, L. 1912. Chinois et kumquat. Revue Horticole [Paris] 84: 564–567. 3 figs.
Trabut, L. 1914. Le kumquat. Bulletin Agricole de l'Algerie et de la Tunisie II 20: 2–11.
Volckamer, J.C. 1708-14. Nürnbergische Hesperides, oder gründliche Beschreibung der edlen Citronat- Citronen- und Pomeranzen-Füchte… Bei dem Authore, Nürnberg. 2 vol.
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Citrus ID Edition 2
October, 2011
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