Botanical Origin—The genus Cinchona constitutes together with Cascarilla (including Buena and Cosmibuena), Remijia, Ladenbergia, Macrocnemum, and about 30 other nearly allied genera, the well-characterized tribe Cinchoneæ of the order Rubiaceæ. This tribe consists of shrubs or trees with opposite leaves, 2-celled ovary, capsular fruit, and numerous minute, vertical or ascending, peltate, winged, albuminous seeds.
(A.) Remarks on the genus.—The genus Cinchona is distinguished by deciduous stipules, flowers in terminal panicles, 5-toothed superior calyx, tubular corolla expanding into 5 lobes fringed at the margin. The corolla is of an agreeable weak odour, and of a rosy or purplish hue or white. The fruit is a capsule of ovoid or subcylindrical form, dehiscing from the base (the fruit-stalk also splitting) into two valves, which are held together at the apex by the thick permanent calyx. The seeds, 30 to 40 in number, are imbricated vertically; they are flat, winged all round by a broad membrane, which is very irregularly toothed or lacerated at the edge.
The Cinchonas are evergreen, with finely-veined leaves, traversed by a strong midrib. The thick leafstalk, often of a fine red, is sometimes a sixth the length of the whole leaf, but usually shorter. The leaves are ovate, obovate, or nearly circular; in some species lanceolate, rarely cordate, always entire, glabrous or more rarely hirsute, often variable as to size and form in the same species.
Among the valuable species, several are distinguished by small pits called scrobiculi, situated on the under side of the leaf, in the axils of the veins which proceed from the midrib. These pits sometimes exude an astringent juice. In some species they are replaced by tufts of hair. The young leaves are sometimes purplish on the under side; in several species the full-grown foliage assumes before falling, rich tints of crimson or orange.
The species of Cinchona are so much alike that their definition is a matter of the utmost difficulty, and only to be accomplished by resorting to a number of characters which taken singly are of no great importance. Individual species are moreover frequently connected together by well-marked and permanent intermediate forms, so that according to the expression of Howard, the whole form a continuous series, the terminal members of which are scarcely more sharply separated from the allied genera, than from plants of their own series.
As to the number and value of the species known, there is some diversity of view. Weddell, in 1870, enumerated 33 species and 18 sub-species, besides numerous varieties and sub-varieties. Bentham and Hooker, in 1873, estimated the species as about 36.
Kuntze, in the book quoted at the end of the present article, proposed to reduce all the species to the four following:
1. Cinchona Weddelliana O. Kuntze, nearly answering to C. Calisaya Weddell.
2. C. Pavoniana O. Kuntze, including C. micrantha Ruiz and Pavon and several allied plants.
3. C. Howardiana O. Kuntze, constituted of C. succirubra Pavon and a few other species of former authors.