Choisya ternata Kunth (Rutaceae family) are bushy shrubs of 2 m maximum height. They are ornamental, with persistent leaves and white flowers resembling those of orange trees whence their French name: Oranger du Mexique or English name: Mexican orange (). In Germany they are called Dreizahlige Choisya, and in their native country, Mexico, they are known as Hierba del Clavo, Flor del Clavo, Clavillo, and Clavo de Olor. The genus name is dedicated to the Genevan naturalist, Choisy (1799-1859).
Botanical Traits and Classification
The genus Choisya was studied by Gray (1888), Standley (1923), and later by Muller (1940). Choisya neglecta is the nearest to Choisya ternata, differing only by smaller leaflets and inflorescences. The other species counted by Muller are sometimes classified in a related genus, Astrophyllum, but according to Dreyer et al. (1972), the comparison of the chemical constituents of Choisya ternata, Choisya mollis, and Choisya arizonica cannot justify this distinction. Therefore, the genus Choisya contains seven species: C. ternata Kunth, C. neglecta Muller, C. dumosa A. Gray, C. mollis Standley = Choisya dumosa var. mollis Benson, C. arizonica Standley = Choisya dumosa var. arizonica Benson, C. palmeri Standley, and C. katherinae Muller.
Choisya ternata was first described in 1823 by the German botanist Kunth when he classified the plants harvested in North America by Humboldt and Bonpland. This species fructified infrequently, which may be due to irregular meiosis, the irregularities being manifested by a few lagging chromosomes at the time of anaphase. Moreover, pollen is often defective. According to Desai (), Choisya ternata may be a hybrid; however, some seeds were described by Boudouresques (1895).
Choisya ternata originated from the central and southern mountains of Mexico. The plants are seldom known growing wild. They were already widely cultivated in their native country when harvested by Humboldt and Bonpland. These cultivated plants are, in fact, very similar to those encountered in nature ().
Biology and Propagation
In Europe, Choisya ternata blossoms in April-May. After the spring flush, there are usually two other flushes of the same shoot within the same season, each of which may be accompanied by the development of lateral inflorescences as in the spring flush. Details on the endorhythmic development in C. ternata have been given by Guedes (1980). Even in their native region, the fruit-bearing is very infrequent. Thus, the species is propagated vegetatively. Micropropagation of Choisya ternata was recently achieved in France (Nursery Salle-Proust, St-Cyr-en-Val). Rooted plants of 8-10 cm in height have been commercialized since 1991. The plants are adapted in greenhouses and sold in a mixture of peat and perlite.
In 1895, Boudouresques studied this species and undertook the first pharmacological tests by experimenting the effects of aqueous extracts of leaves on himself: he found them tonic and appetizing. On the other hand, the oil is strongly repulsive. In 1923, Standley reported that Mexican people employed infusions of leaves for their antispasmodic and “stimulant properties”; Choisya ternata was registered in the 4th and 5th editions of the Mexican Pharmacopoeia. As far as we know, the present use of C. ternata is not widespread. However, it may be recalled that some Rutaceae-related species, such as Ruta graveolens and Ptelea trifoliata, which have a similar chemical constitution, are still used therapeutically ().
By using different strategies, in vitro cultures of Choisya ternata were established. Great variations exist within the populations of strains.
The use of inherent variability in vitro is an efficient procedure to obtain high-platydesminium-accumulating cell lines. Some of them accumulated the alkaloid in higher amounts than the mother plant. However, high-balfourodinium-accumulating lines were not obtained. The best method was the cloning of protoplasts obtained from mesophyll cells: with this procedure the highest balfourodinium-accumulating lines (about 700 µg/g on a dry weight basis) were obtained, a concentration far lower than that found in leaves. Other strategies than strain selection are necessary for achieving high-balfourodinium production in cultures of Choisya ternata. On the other hand, some strains can biotransform ellipticine by a process different from those generally encountered with microorganisms, which emphasizes the capacity of in vitro plant cell cultures to obtain new molecules.
Photoautotrophic growth does not allow the restoration of alkaloid biosynthesis capacities. Nevertheless, the presence of sterols not found in the whole plant shows that some original substances can be produced by photoautotrophic cultures.
Because of their easy cultivation procedures, cultures of Choisya ternata prove to be a good model for studying the enzymes involved in the biosynthetic pathway of furo- and dihydrofuroquinolines.
Selections from the book: “Medicinal and Aromatic Plants V”, 1993.