The genus Cinchona is classified in the Tribe Cinchoneae, and includes at least 23 species of trees and shrubs that are native to the Andes of South America and the mountains of southern Central America. The trees have showy white, pink, or purple flowers that are generally pollinated by butterflies and hummingbirds, and dry capsular fruits with flat, papery seeds that disperse on the wind. Most of the species are found in the Andes and adjacent lowlands of Ecuador and Peru, and most have rather restricted ranges. Cinchona pubescens has the broadest natural range and has been cultivated in other areas; in continental regions it spreads little beyond cultivation, but in the Galapagos and some other tropical islands it has become an invasive weed.
The bark of several species of Cinchona has been the source for some centuries of the febrifuge chemical quinine, effective against malaria. In the Andes the bark has been widely harvested from wild Cinchona trees, which has reduced their populations. Several species and numerous hybrids have been cultivated in warm humid regions world wide, particularly India and southeastern Asia. Commercially useful quantities of quinine are found in the bark of only two main species, C. pubescens, which has sometimes been cultivated under the name C. succirubra, and C. calisaya. Cinchona calisaya has sometimes been cultivated under the name C. ledgeriana and has also been sometimes confused with C. officinalis, however C. officinalis is a separate species found the Andes of southern Ecuador that does not contain quinine in its bark. Some other Rubiaceae also produce quinine and are used locally as malaria remedies, for example Hintonia and perhaps Coutarea in Mexico and northern Central America. Trees of Cinchona are also prized for their good wood.
The flowers are diurnal, and white, pink, or purple and generally very hairy or fuzzy in the mouth of the corolla tube. They are apparently pollinated mainly by butterflies and hummingbirds. The flowers are distylous: some plants have only flowers of the long-styled ("pin" form), with the stigma positioned at the top of the corolla tube and the anthers positioned below, inside the tube; other plants have short-styled flowers ("thrum" form) with the reciprocal or opposite arrangement, with the anthers positioned at the top of the corolla tube and the stigmas below, inside the tube. This reciprocal arrangement is believed to promote out-crossing and diminish pollination by the same flower form, by depositing pollen on different parts of the pollinator so that the pollen from the short-styled flowers is transferred to the stigmas of the long-styled flowers, and vice versa. In general the distylous type of flower also has incompatibility at the cellular level, so the pollen of long-styled flowers generally has a very low success rate in other long-styled flowers, and vice versa. The fruits are dry, rather woody capsules that open to release numerous small, papery, flattened seeds that are dispersed by the wind.
Cinchona is notable within the Rubiaceae at least for its ability to hybridize, and as noted by Andersson (1998) in some areas where two species' ranges connect, the boundaries between the species are not entirely clear due to hybrid swarms of plants with intermediate conditions. Many commercially grown plants of Cinchona are of hybrid origin and thus do not correspond to any wild or named species.
Cinchona has been confused with the related Rubiaceae genus Ladenbergia. In fact the separation of these was not clear for many years, but Andersson (1998) showed that species of Cinchona have white, pink, or purple flowers that open during the day and are hairy or fuzzy at the top of the tube and on the lobes, while Ladenbergia has bright white flowers that open during the night, and are not hairy or fuzzy at the top. Otherwise these two groups are difficult to separate. Previously they were sometimes separated by their fruits, which supposedly opened from the bottom in Cinchona vs. from the top in Ladenbergia, but Andersson showed that in fact the pattern of opening varies within both genera so this distinction does not actually work.
Many species of Cinchona are uncommon today, and several are formally considered threatened. The trees are found in well preserved, usually isolated montane forests, although most of them seem to grow in disturbed areas as well when they are not cut down. Cinchona populations have been significantly reduced or extirpated by human exploitation, both harvesting the bark and taking whole trees for their good wood. In general folk taxonomy the "cascarilla" or "quina" tree is still considered fairly common in the Andes, but usually the plants identified with these names today are Ladenbergia oblongifolia, a common species found widely in secondary vegetation, or Elaeagia and various other species of Rubiaceae with well developed ligulate stipules that are held erect in bud. Ladenbergia oblongifolia does have some bitter alkaloids in its bark, but these are produced in very low quantity and this species is not a useful source of quinine. However Ladenbergia oblongifolia is today starting to be cultivated as "Cinchona" due to lack of botanical knowledge and, apparently, a shift in the folk taxonomy as younger generations no longer see the true Cinchona species.
The multidisciplinary international project The Quest for Cinchona - A Phylogenetic Tale , based in Copenhagen, addresses the biogeography, alkaloid chemistry, and conservation of Cinchona and related plants that are sources of quinine in South America. See their website and publications for information on those topics.
The name Cinchona was one of the first published for Rubiaceae, and for more than half a century afterward this name was used for most of the Rubiaceae plants with dehiscent capsules and winged seeds. However today the plants originally included in Cinchona are separated into more than a dozen different genera. This broad use of the name Cinchona created some taxonomic confusion, as did the large number of studies in the 18th and 19th century that attempted to make a taxonomy for the cultivated trees of Cinchona. These studies of cultivated trees were done before the concepts of species and hybrids were well developed, and often did not distinguish these types of plants or relate the cultivated, usually hybrid plants to the wild, "species" plants. Also many Cinchona names used for cultivated plants were never actually scientific names, they were commercial designations or breeds. Additionally, in the 18th and 19th century two other names were commonly used for Cinchona, Quinquina and Cascarilla. These are not accepted scientific names today, as discussed on their respective web pages.
Author: C.M. Taylor.
The content of this web page was last revised on 29 Nov. 2016.
Taylor web page: http://www.mobot.org/MOBOT/Research/curators/taylor.shtml