Swingle and Reece (1967) noted that: "The discovery that a small-fruited plant, obviously a kumquat, was masquerading under the name Atalantia hindsii led Swingle to a study of the group, with the result that in 1915 he proposed a new genus, Fortunella, to include all the species of kumquats that had hitherto been placed in Citrus and Atalantia. Important characters were brought to light that separated Fortunella sharply from both Citrus and Atalantia. Further studies have disclosed the fact that a number of varieties of kumquats found in cultivation in China and Japan are merely hybrids due to chance cross-pollinations by insects in village or dooryard groves. The Meiwa variety (called Chintan in China), at first considered by Swingle to be a good species (Fortunella crassifolia), and the Changshou kumquat, named as a species (F. obovata ) by Tanaka, are both doubtless mere garden hybrids not entitled to rank as species. This decision helps greatly in clarifying the taxonomic status of the genus."
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; prickles absent or not persistent. Petiole glabrous or pubescent, length short or medium; wings absent, narrow or wide, adjoining the blade, tucking beneath blade or absent. Leaflets one, margin entire, crenate/crenulate, bluntly toothed or serrate/serrulate, shade leaflet blades flat or weakly conduplicate, sun leaflet blades flat or weakly or strongly conduplicate. Scent of crushed leaflets sweetly orange-like, spicy or peppery, freshly lemon-like, somewhat to strongly malodorous, mandarin-like or not scented. Fruit broader than long, as broad as long, or longer than broad; rind variegated, medium green (4), light green with some break to yellow (5), 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 group:
"The species of Fortunella, in spite of their small number, have been very inadequately studied, largely because, until recently, only one species was cultivated in either Europe or the United States and the others were represented only by scanty herbarium material in a few of the largest herbaria."
"There are also intergeneric hybrids resulting from cross-pollinations between Fortunella and Citrus found in cultivation in China and neighboring countries. One such hybrid, the Calamondin, has been erroneously named as a species of Citrus (it was called C. microcarpa by Bunge and C. mitis by Blanco). However, the whole complex intergeneric hybrid problem of Fortunella has been materially clarified by the making of many accurately safeguarded cross-pollinations of Fortunella with Citrus, Poncirus, Microcitrus, and Eremocitrus. This work, conducted under Swingle's direction in the Agricultural Research Service, led to the creation of a bewildering group of strange hybrids that would have been very disturbing to the taxonomist if their origin were not definitely known."
"Several species of Fortunella have developed a degree of resistance to winter cold and at the same time an even more important physiological peculiarity, namely, a very pronounced winter dormancy that permits them to pass through weeks of warm weather without starting growth or flowering. This quality, possessed in much higher degree by the kumquats than by any other citrus fruit tree (not excluding the winter-hardy Poncirus), makes them of prime importance in the breeding of new types of hardy citrus fruit trees (especially for producing acid citrus fruits) able to grow in much colder regions than the lemon or lime (both notoriously deficient in winter dormancy and hence easily pushed into growth by a few days of untimely warm weather in winter or early spring).
Fortunella hybrids will in all probability be produced in large numbers in the future. Their study is likely to prove of great importance in bringing about a just appreciation of the hybrid problem in the taxonomy as well as in the breeding of citrus fruit trees. Since Fortunella, with its few species and its already well-understood intergeneric hybrids, constitutes a veritable microcosm of the citrus world, it will doubtless prove of great help in understanding the much more complex and still only imperfectly studied species and hybrid problems in the genus Citrus itself."
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.
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.
Citrus ID Edition 2
October, 2011
idtools.org
