Limonia Sec. III, Hesperethusa Engl. (sec. Cottin 2002)
Hesperethusa M. Roem. (sec. Swingle and Reece 1967; sensu Tanaka sec. Cottin 2002); Naringi Adans. (sec. Mabberley 2004, Bayer et al. 2009)
Crown compact or dense, not weeping. First-year twig surface glabrous; second- or third-year twig surface mottled; thorns straight; prickles absent or not persistent. Petiole glabrous, length medium or long; wings narrow, adjoining the blade. Leaflets five to seven, margin crenate/crenulate or serrate/serrulate, rachis wings wide, shade leaflet blades flat or weakly conduplicate, sun leaflet blades flat or weakly conduplicate. Leaflets not scented when crushed. Fruit as broad as long or longer than broad; rind black; rind texture smooth (1-3); firmness membranous; navel absent; flesh red/purplish-tinged.
Swingle and Reece (1967) provided the following additional notes on the species:
"Slender, thorny trees or shrubs; leaves persistent, odd-pinnate; petioles and rachis broadly winged (petioles sometimes more narrowly winged); inflorescences axillary, few-flowered; flowers small, 4-merous (except stamens, twice as many as petals); ovary with 4 locules, 1 ovule in each locule; fruits small, 1 or more of the 4 segments with a single seed, surrounded by scanty, bitterish pulp containing large rudimentary sessile pulp-vesicles of irregular size and shape; seeds hard, smooth, germinating with epigeous cotyledons.
Hesperethusa has apparently no near relatives, differing widely from all the other genera of the Citrus Fruit Trees except Citropsis in having odd-pinnate leaves with three to four pairs of small, opposite, crenate leaflets and broadly winged petioles and rachis segments. Pinnate leaves were undoubtedly borne by the remote ancestors of all the Citrus and Citroid Fruit Trees (the tribe Citreae). The characters persist today only in two out of the thirteen genera (Hesperethusa and Citropsis)of the second subtribe, Citrinae, and in two out of the seven genera (Feronia and Feroniella) of the third subtribe, Balsamocitrinae. None of the eight genera in the first subtribe, Triphasiinae, have pinnate leaves. In other words, only two of the three subtribes of the tribe Citreae have genera with pinnate leaves, and out of a total of twenty-eight genera in the tribe only four have pinnate leaves.
Hesperethusa has some other points of similarity with the African genus Citropsis aside from pinnate leaves. The seeds of both genera have a hard testa, cream-yellow in color, composed of radial prismatic cells, some with very thick walls. The little known Citropsis daweana from Portuguese East Africa has the smallest leaflets of any of the species of Citropsis, with widely winged rachis segments but nearly wingless petioles, making the leaves look somewhat like those of certain forms of Hesperethusa crenulata.
The very small fruits of this monotypic genus show rudimentary pulp-vesicles attached to the dorsal wall and apparently also to the base of the locule. There are relatively few of these pulp-vesicles in each locule of the developing fruit; they are not clearly differentiated into basal and apical portions but are irregularly rounded and seem to be thin-walled; they vary greatly in size, and are often polygonal from mutual pressure. These rudimentary pulp-vesicles can be seen in the sections of the fruits of paratypic material in the Kew Herbarium which was collected by Roxburgh in the last quarter of the eighteenth century and from which he drew up the description of Limonia crenulata, the type species of the genus.
The pulp-vesicles of Hesperethusa that arise from the dorsal wall of the locule appear like small vesicles adhering to the wall by a broad base and are broader than high. The few pulp-vesicles that arise from the base of the locule are more or less slender and elongated but do not have any clearly marked stalk. The shapes taken by the pulp-vesicles seem to be governed by the free space available into which they can expand as they develop. The pulp-vesicles attached to the dorsal wall are somewhat like those of Pleiospermium in shape but they do not show any definite cortical layer and furthermore do not show any degenerations of the central portion into an oily or resinous (?) mass.
Hesperethusa can be grafted on Citrus and such grafts live and grow for many years.
Dr. Anna E. Jenkins (1936, pp. 71, 73) discovered on the fruits of Hesperethusa from India a fungus, Elsinoë sp., very like the scab fungi, E. fawcettii and E. australis, that attack species of Citrus."
"Severinia and Hesperethusa have peripheral pulp-vesicles that are irregular in shape and size and little differentiated in structure."
"The genus Hesperethusa in group A resembles Citropsis in group B in its leaf and seed characters but has much smaller fruits with much less definitely organized pulp-vesicles."
"This group includes the five genera of the subtribe Citrinae, Severinia, Pleiospermium, Burkillanthus, Limnocitrus, and Hesperethusa, which show the most primitive pulp-vesicles, lacking the stalks of the pulp-vesicles of group C (the True Citrus Fruit Trees) and the definite conical shape with broad sunken bases of those of group B (the Near-Citrus Fruit Trees)."
"The pulp-vesicles of Hesperethusa are irregularly rounded or even polygonal from natural pressure, without specialization of form or regularity of arrangement as far as can be learned from the material now available for study. Hesperethusa, like Citropsis, can be grafted on Citrus, and vice versa."
"Severinia differs decidedly from Hesperethusa in having simple leaves and wingless petioles."
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.
Jenkins, A.E. 1936. A Sphaceloma on fruit of Hesperethusa crenulata, a remote citrus relative from India. Phytopathology 26: 71–73.
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.
Search for this cultivar in NCBI Entrez or NCBI Nucleotide
Citrus ID Edition 2
October, 2011
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