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Citrus ID







Cultivar or taxon


Citrus L. (sec. Mabberley 2004, Bayer et al. 2009); Microcitrus Swingle (sec. Swingle and Reece 1967; Cottin 2002)



Swingle and Reece (1967) noted that:

"Microcitrus is a primitive genus related to Citrus; perhaps some of its species are very like the ancestral species from which Citrus developed."

"The six known species of Microcitrus are the result of millions of years of slow evolution from a primitive ancestral type. From this ancestral type arose the genus Eremocitrus, with marked xerophytic adaptations and two ovules in each locule of the ovary, and the genus Microcitrus, with more numerous ovules in each locule.

This ancestral type probably resembled somewhat M. warburgiana, the New Guinea species, which has small leaves and small, nearly spherical fruits. From such an ancestral form, one line of evolution produced the so-called native orange, round lime, or Dooja (M. australis), that grows to a large tree and has subglobose fruits much larger than those of M. warburgiana, with long, slender, pointed, more or less twisted pulp-vesicles; another line of evolution culminated in M. inodora and M. maideniana, highly specialized forms showing adaptations to tropical rain forests, with large leaves and paired spines; a third line of evolution led to the small-leaved, somewhat xerophytic species M. australasica and M. garrowayi, both with long-ovoid or very elongate-cylindric fruits.

These remarkable citrus fruits are extremely interesting, in that they show how evolution has proceeded in regions isolated as Australia and New Guinea have been during the last twenty or thirty million years since they were cut off from all other land masses The evolution of other citrus fruits is not so easily followed, since Citrus, Fortunella, and Poncirus did not originate in regions that were geographically isolated in definitely dated geologic eras."



Crown compact or dense, not weeping. First-year twig surface glabrous; second- or third-year twig surface striate; thorns straight; prickles absent or not persistent. Petiole glabrous, length short or medium; wings absent, if present, narrow, adjoining the blade. Leaflets one, margin entire (by misinterpretation) or bluntly toothed, shade leaflet blades flat or weakly conduplicate, sun leaflet blades flat or weakly conduplicate. Scent of crushed leaflets sweetly orange-like, spicy or peppery, or not scented. Fruit as broad as long or longer than broad; rind black, red or pink, dark green (3), medium green (4), light green with some break to yellow (5), green-yellow (6), or yellow (7-10); rind texture slightly rough (4-5), medium rough (6-7), or rough (8); firmness leathery; navel absent; flesh green/greenish.

Swingle and Reece (1967) provided the following additional notes on the genus:

"To judge from the thick leaves that become glaucous as they develop, the plants of this genus are very probably somewhat xerophytic, like Microcitrus of Australia, but are not so well adapted to withstand long-continued drought and hot, dry winds as the truly xerophytic Eremocitrus, also of Australia."

In the analysis by Bayer et al. (2009), species of Microcitrus (as recognized by Swingle) formed a strongly supported clade including the Australian xerophytes Eremocitrus glauca (= Citrus glauca sensu Bayer et al. 2009).



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.

Hodgson, R.W. 1967. Horticultural varieties of Citrus. In: Reuther, W., H.J. Webber, and L.D. Batchelor (eds.). The Citrus industry, rev. University of California Press.

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.



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Citrus ID Edition 2
October, 2011