The Meliaceae family is found in the Americas, Africa and Asia, and includes about 50 genera and 1,000 species (Watson and Dallwis, 1995). In the neotropics, 8 genera have been described: Cabralea, Carapa, Cedrela, Guarea, Ruegea, Schmardea, Swietenia and Trichilia, with Swietenia and Cedrela being the most important from the forestry point of view (Pennington and Styles, 1975; Holdridge, 1975; Pennington, 1981). These latter ones will be dealt with in this document.
The most up-to-date review of Swietenia and Cedrela is by Pennington (1981), in which the author worked on Cedrela jointly with Germán; the document presents takonomic keys for Swietenia and Cedrela, which allow the identification of the species recognized by the authors. In more recent studies, Reynel and Pennington (1989) study the genus Cedrela in Peru and cite the presence of species of the genera Ruegea and Schmardea in the country; these had not earlier been reported to be present in the neotropics.
This genus is found only in the neotropics (Figueroa, 1994) and consists of three species: Swietenia mahagoni Jacq., Swietenia macrophylla King, and Swietenia humilis Zucc.; and two natural hybrids: one is a product of a cross between S. macrophylla and S. humilis and is found in the areas of the distribution range in which the two species overlap; the other is a cross between S. macrophylla and S. mahogani, named S. x aubrevilleana which has been found close to plantations of the two species (Pennington, 1981).
Known as “caoba” and “caoba Hondureña” in Spanish, “mogno” in Portuguese and “mahogany” or “bigleaf mahogany” in English, the range of distribution of this species runs from Mexico to Brazil. In Mexico it is found from south of Tamaulipas, and follows the Atlantic coastline to the Yucatan peninsula; it is present in Central America, from Belize to Panama; it continues through the northeast section of South America throughout the periphery of the High Amazon in Colombia, Venezuela, Ecuador and Peru through to Bolivia and the southern Amazon in Brazil (Miranda, 1952 and 1975; Pennington and Sarukhán, 1968; Salas, 1993; Figueroa, 1994). S. macrophylla has been included in Appendix III of CITES (Convention on International Trade in Endangered Species) at the request of Costa Rica, and for this reason, a certificate of origin is needed in order to export wood and wood products (CITES, 1995).
Known as “caoba de las Indias Occidentales” or “West Indian mahogany” and “mahogany”. The species is native to southern Florida, the Keys, the Bahamas, Cuba, Jamaica and the Dominican Republic.
The species was introduced into Puerto Rico, the Virgin Islands, the Bermudas, the Lesser Antilles, Trinidad and Tobago, and southward to South America and the island of Curaçao; it has also been introduced into Hawaii, the Solomon Islands, India, Sri Lanka and Fiji, among others. In its natural range of distribution the species occurs in a series of isolated stands, in pure stands or in mixture with other species (Little, Wadsworth and Marrero, 1967; Little, 1978; and Francis, 1991).
Referred to as “Pacific mahogany”, “caobilla” or “cobano”. The species is distributed within a narrow band along the Pacific Coast stretching from Sinaloa, Mexico, with a isolated occurrence in eastern Guatemala located east-southeast of Lake Izabal, down towards Punta Arenas in Costa Rica (Miranda, 1952 and 1975; Whitmore and Hinojosa, 1977; Salas, 1993).
The distribution of S. macrophylla and S. humilis overlaps in at least three areas; one in Mexico (in the Tehuantepec isthmus), one in Guatemala and another one in Costa Rica (Whitmore and Hinojosa, 1977), where there have also been reports of natural hybrids between the two species. S. humilis has been included in Appendix II of CITES, which means that in order to be marketed, Chapter Four of the Convention signed by the member countries must be complied with, which states the obligation of obtaining from the competent authorities the permission to export or import specimens or products of the species.
The broad ecological and geographic range over which Swietenia species are distributed and the ease of hybridization between them suggest that a high degree of genetic diversity is likely to be available in the natural populations (Newton et al, 1993b).
It has, in fact, been confirmed that the majority of the species of the Meliaceae have a high degree of variability. In the case of Swietenia, the three species are inter-fertile (Styles in Pennington, 1981; Francis, 1991) and produce hybrids when brought together. Hybrids occur both where natural distribution overlaps and where plantations have been established of hybridising species. Taxonomic identification is difficult in such areas.
Marquetti et al (1975) describe the taxonomy and distribution of the genus Swietenia: S. mahogoni, S. macrophylla and S. humilis, citing examples of observations made in Cuba and the Caribbean islands and reporting on the occurrence of intermediate forms between S. mahagoni and S. macrophylla where these species grow closely together, presenting evidence from local studies that the intermediate form found in Cuba is an F1 hybrid.
There are reports of natural hybrids of S. humilis x S. macrophylla in the northeast of Costa Rica (Holdridge and Poveda, 1975; Whitmore, 1983), in areas where the morphology of the leaf as well as the size of the fruit of these species show a gradual climal change. Hybrids have appeared spontaneously in many islands of the Caribbean, in Central America and in Mexico, where plantations of the cited species have been established (Whitmore and Hinojosa, 1977; Styles in Pennington, 1981). In Mexico a possible hybrid of S. macrophylla x S. mahagoni was detected in the Los Mangos forest nursery in Chetumal, Quintana Roo, as reported by Chavelas, Borja and Lopez Suarez (personal communication).
Whitmore and Hinojosa (1977) analyze the relations of the three species of Swietenia, review S. macrophylla x S. mahagoni hybrids from the taxonomic point of view, and describe two presumed hybrids of S. humilis x S. macrophylla and S. humilis x S. mahagoni; the authors consider that these latter are ones to be insufficiently known.
The capacity for hybridization greatly influences the genetic composition of individual stands. For example, the populations of Swietenia in Puerto Rico, constitute a cluster of hybrids with F1, F2 and F3 generations and back-crosses between the two principal species, including individuals with leaves, bark, fruits and seeds with the characteristics of one or the other of the parent species (Whitmore and Hinojosa, 1977, Francis, 1991).
The occurrence of hybrids has important implications for defining strategies for genetic conservation and for genetic improvement programmes. For example, the hybridization with the introduced Swietenia macrophylla in Puerto Rico can be considered a cause of genetic erosion in the native Swietenia mahagoni. Genetically pure populations of the two species might disappear in Puerto Rico with the passage of time (Newton et al, 1993b).
Francis (1991) points out that inter-specific Swietenia hybrids have been observed and utilized in various areas, as they have shown more rapid growth than their parent species in early tests. It has been reported that the F2 generation segregates according to Mendelian rules in the proportion 1:2:1 (Marquetti et al, 1975).
Kageyama (1996) reports on the existence of a presumed hybrid of Swietenia mahagoni and S. macrophylla, known as S. x aubrevilleana, which combines good growth, good form and resistance to drought. The hybrid occurs spontaneously in areas where the two parent species were planted in proximity; this hybrid has been reported in Taiwan and Indonesia.
There is some evidence which supports the assumption that S. humilis and S. macrophylla could be the same species, and there is some work in progress to clarify their taxonomic relationship1 (Germán, 1996; Navarro, 1996).
1 Information provided by Biol. María Teresa Germán, Instituto de Biologia, UNAM, Mexico (1996).
The genus Cedrela was described by P. Browne in 1756. In 1759 Linneaus described C. odorata. Since then, 69 species have been placed in this genus, including species which occur in the Americas, India, Southeast Asia and Australasia. In 1960 Smith carried out a review of the genus and, based on this study, the Asian and Australasian species were placed in the genus Toona, leaving the genus Cedrela with only nine species, all of them occurring in the Americas (Lamb, 1968).
In 1981 Styles (in Pennington, Styles and Taylor, 1981) reviewed the genus with M.T. Germán. These authors recognize 7 species: Cedrela fissilis Vellozo; C. lilloi C. De Candolle; C. montana Moritz ex Turczaninov; C. oaxacensis C. De Candolle & Rose; C. odorata Linnaeus; C. salvadorensis Standley and C. tonduzii C. De Candolle. The same authors consider four species insufficiently known: C. angustifolia Moçiño and Sessé Ex P. de Candolle; C. discolor S.F. Blake; C. imparipinnata C. de Candolle and C. weberbaueri Harms. In 1990, Calderón de Rzedowski G. and Germán M.T., in reporting on the Meliaceae of the Bajío region (Mexico), recognized the existence of Cedrela dugesii Watson, which is considered by various authors a synonym of C. odorata.
Marquetti (1990) notes the existence of a natural hybrid, product of a cross between C. odorata L. x C. cubensis (Bissé), which, according to the author, demonstrates heterosis and shows better growth when compared to the parent species.
The distribution of the principal species of Cedrela in the neotropics is as follows:
C. oaxacensis is endemic to the Balsas River basin in Mexico, occurring in dry areas of the States of Morelos, Guerrero and Oaxaca. In certain areas it is associated with Pinus species. Populations consist of small trees of no actual economic importance (Standley and Steyermark, 1946; Lamb, 1968; Pennington, 1981).
C. salvadorensis, occurs in dry tropical forests, from the State of Jalisco to Chiapas in Mexico, continuing through Central America to the north of Panama, generally in dry tropical or deciduous humid forests, on stony and calcareous soils, and generally at altitudes of less than 1,000 meters above sea level, although occasionally the species has been reported to grow at 1,500 meters (Standley and Steyermark, 1946; Lamb, 1968; Pennington, 1981).
C. tonduzii is found from Oaxaca and Chiapas in Mexico through to Panama in Central America. It is a large tree, with good wood properties; on occasion it grows in association with Pinus and Liquidambar species, at altitudes of 1,100 to 2,800 meters above sea level, generally on soils that are volcanic in origin, fertile and well drained. It is of potential importance in plantations (Standley and Steyermark, 1946; Lamb, 1968; Pennington, 1981).
C. odorata is distributed from the north of Mexico in the State of Sinaloa (26°N) to Chiapas on the Pacific coast, and from the state of Tamaulipas to Campeche, Yucatan and Quintana Roo on the Atlantic coast, continuing down through Central and South America to the Argentine provinces of Misiones and Tucuman (28°S). It is also found in the Caribbean Islands. In general, the species grows on well-drained, fertile soils. It is found in tropical as well as in dry and humid sub-tropical forests, at altitudes of up to 1,200 meters (Standley and Steyermark, 1946; Verduzco, 1961; Lamb, 1968; Holdridge, 1976a; Pennington, 1981; Ponce, 1996), it has been observed in Ocosingo, Chiapas, up to 1,800 meters above sea level, and in these areas grows in association with Pinus species.
The distribution of C. lilloi C.D.C is confined to South America. It is found in Bolivia, Peru, Brazil and Argentina. In Bolivia and Argentina the species is found in mountain forests, at altitudes from 1,000 to 3,400 meters above sea level, but is also reported to occur at altitudes as low as 800 meters. In Peru, it is found in high valleys where it forms extensive forests and is also planted for shade. It is a cold-resistant species, deciduous in winter, and is of importance as a producer of wood for local use (Standley and Steyermark, 1946; Lamb, 1968; Pennington, 1981).
C. montana is a species found in the cloud-forest belt and in the “paramo” areas. It can be seen frequently in open pastureland and in abandoned agricultural areas. In South America, it occurs in the same areas as C. lilloi, with which it is associated in the highlands of Venezuela and Peru (1,400 to 3,100 meters above sea level). It is a locally important species (Standley and Steyermark, 1946; Lamb, 1968; Pennington, 1981).
C. fissilis is found from Costa Rica in Central America to southern Brazil and northern Argentina in South America. The wood of this species is considered inferior to that of C. odorata, nonetheless in some areas wood of the two species is marketed interchangeably. C. fissilis is extremely variable especially in terms of leaf morphology. This has been reflected in a large number of synonyms and varieties that have been described for this species (Standley and Steyermark, 1946, Lamb, 1968; Pennington, 1981).
In the present document, only Cedrela odorata L and C. fissilis Vellozo will be dealt with in some detail.
Known as “cedro Hembra”, “Spanish cedar”, “royal cedar”, “red cedar” or “cedar”, Cedrela odorata is the most important and widely distributed species of the genus Cedrela. Its wood is in high demand in the American tropics, as sawnwood, plywood, for molding and cabinet work. Having an agreeable, pleasant scent its wood is also used as packaging for Havana cigars.
The species ranges from northern Mexico, through Central America and the Caribbean islands, to Brazil; it is found in tropical and sub-tropical and semi-humid climates. It is found from sea level to close to 3,000 meters above sea level, in Bolivia (Lamb, 1968). In Chiapas, Mexico, C. odorata grows from sea level up to 1,800 meters (Ocosingo, Chiapas), and is found at higher altitudes mixed with Pinus species. It is usually found on well-drained soils. The species tolerates prolonged periods of drought (Lamb, 1968; Salas, 1993); it also grows in volcanic soils (Pennington and Sarukhán, 1968).
As seen above, Cedrela odorata is widely distributed throughout the neotropics and grows in mixed stands. Individuals of this species are few in number and are widely dispersed. Cedrela odorata is not generally considered to be threatened in the main parts of its distribution range. It is represented in Protected Areas, in natural forests, and it is common to find individuals of the species planted in urban areas.
Reynel (1988) notes that Cedrela odorata is not under threat in Peru, that populations of the species remain, and that many of the Protected Areas in the country contain individuals of the species. However, the author warns that some populations of this and other Cedrela species are drastically being reduced.
On the Yucatan Peninsula, Mexico, is it common to observe individual mature trees of Cedrela odorata, with diameters of up to 60 centimeters planted outside private houses; the owners consider that the tree represents a type of “savings” account for the future. It is important to note that part of the wood which is presently marketed, especially in Yucatan, comes such individual, planted trees.
Currently, in the States of Campeche and Yucatan, Mexico, close to 3,500 hectares of Cedrela odorata plantations have been established and the species is a preferred one for incorporation into agroforestry systems.
Known as “cedar”, “rose cedar”, “red cedar”, or “white cedar”, this tree flowers during the months of August and September. Its fruit ripens while the tree is leafless, between June and August. It annually produces a large quantity of viable seeds (Lorenzi, 1992).
The species ranges from Costa Rica to the north of Argentina. In Brazil it is found from Rio Grande del Sur to Minas Gerais, in semi-deciduous forests and in the Atlantic Forest. It is also found in other areas throughout Brazil, although in lesser density (Lorenzi, 1992). The species occurs in very low density (1 tree in 10 hectares) in primary forests, and in greater abundance among secondary vegetation (Kageyama, 1996; Gandara, 1995).
The flowers of species of the Meliaceae have usually been described as perfect, and at times as dioecious/polygamous. Various authors cited by Lamb (1966) note that the flowers are hermaphroditic. This is not always the case according to White and Styles (1963), based on their observations in southeast and central Africa.
Lee (1967) made observations on flowers of Swietenia macrophylla and S. mahagoni, in which he examined in detail the distribution of male and female flowers, the structure of the flowers, the sex of fallen flowers, and reported upon results obtained by bagging flowers with pistils and those with anthers, and from controlled pollination tests. The author concludes that Swietenia flowers are uni-sexual, and that the trees are monoecious with both female and male flowers in each inflorescence. He calls the mixed male/female inflorescences in which hermaphroditic flowers also occur, “tiros”. Styles (1972) is in agreement.
Generally, Swietenia flowers at the beginning of the rainy season: from May to August in Mexico (Pennington and Sarukhán, 1968; Patiño et al, 1983), in the West Indies and in the northern part of South America (Bascopé et al, 1957; Karani, 11973; Raunio, 1973).
In Cedrela odorata the flowers appear when the tree re-sprouts. The large and abundant inflorescences contain many small symmetrical flowers of greyish-white colour. It has been confirmed that the trees are monoecious: both female and male flowers are found in the same inflorescence. The female flowers open before the male flowers. The reproductive cycle of C. odorata is synchronized with the growing season, and thus varies over its range of distribution (Cintron, 1990).
Styles (1972) states that in the neotropical genera of Swietenioideae, which are important from the timber point of view including species such as Swietenia (S. macrophylla King, S. mahagoni (L) Jacq.), Cedrela (the majority of the species) and Carapa (C. guianensis Aubl., C. procera DC Most), the flowers are unisexual and the individuals are monoecious. Styles (1972) also analyzed the flowering biology of the Meliaceae in view of the importance of this factor in tree improvement, and notes that the majority of botanists describe the flowers as hermaphroditic and perfect, due to the fact that each flower possesses both anthers and pistil.
The same author emphasizes that despite the fact that both the anther and the pistil are present in any one flower, both of these are not necessarily effective; in the functional male, the anthers are large, yellow in colour and full of pollen, which is freed by longitudinal cracking during the anthesis. In these flowers, however, in spite of the fact that the ovary and the pistil appear normal in size and form (usually cylindrical or globular), the ovules which are contained them are minuscule and rudimentary, brownish in colour and will generally abort. Also, in this case the ovules do not completely fill the ovary as they do in functional female flowers. This sterile ovary, in which the style is larger than in the functional female flower, is known as “pistiloid”, and it is incapable of further development. After dispersing the pollen, the masculine flower withers and falls to the forest floor (Leb, 1967 cited by Styles, 1972).
Styles (1972) notes that the above systems encourage cross-pollination, but that they do not assure that this cross-pollination will be as effective as in dioecious species or in species in which specific biological systems of self-incompatibility prevail.
However, cross-pollination in some of species of Swietenia, Cedrela and Carapa, is favoured by the fact that the female and the male flowers do not open at the same time (dicogamy). This has been confirmed by field observations in Swietenia by Lee (1968) and in Cedrela by Jones (cited by Styles, 1972).
Howard et al (1995) conducted studies to investigate the role of insects in the pollination of Swietenia mahagony Jacquin in Florida. The only insects that were found to visit the flowers were trips (Thysanoptera), including Frankliniella bispinosa (Morgan), F. insularis (Franklin), Pseudothrips inequalis (Beach/Thripidae), Frankiniella spp, and an unidentified trips larva (Phlaeothripidae). The authors report the presence of trips in percentages which vary from 12% to 59% in the flowers observed in the sampling sites, which were 27 to 82 kilometers from each other. The majority of the flowers sampled were male.
The trips were observed inside the stamen tubes, where there is a large quantity of pollen, and they moved in and out of the stamen tube through a space between this structure and the stigma, usually through a lateral fissure; this forced contact between the insect, the anther and the stigma, facilitating pollination. The majority of the captured trips had Swietenia pollen on their bodies. The authors note that this information will be useful in the genetic improvement of the species.
Styles and Khosla (1976) note that the Meliaceae flowers show structural characteristics pointing to entomophilia, and suggest that nocturnal bees and butterflies might be the primary pollen vectors.
Parraguirre and Calix (1996) are currently working on the reproductive biology of Swietenia macrophylla in San Felipe Bacalar, Quintana Roo, Mexico. Initial observations indicate the presence of trips and other insects on the flowers.
In Brazil, Cedrela fissilis was studied by C. Crestana (Kageyama, 1996). Only trips were found visiting the flowers of that species.
Patiño et al (1983) report on the dates of flowering for Swietenia and Cedrela odorata, indicating that in S. humilis in the States of Guerrero, Veracruz and Oaxaca in Mexico, the flowering period occurs generally between May and June; for S. macrophylla observed in the States of Campeche and Quintana Roo, flowering occurs from April to June, depending on the locality. For Cedrela odorata, the authors indicate May to August as the flowering period in the States of Campeche and Quintana Roo, Mexico. The same authors state that the seed production period in Mexico for S. macrophylla (Campeche and Quintana Roo) and S. humilis (Guerrero and Oaxaca) is in February-April; and for Cedrela odorata, in most parts of its distribution range, in March-April.
Navarro C. and Hernandez (1996) indicate that the seed production period of S. macrophylla in Central America varies largely in function of the areas observed. In Panama, peak production is in November; in Costa Rica from the end of November to the beginning of December; in Nicaragua, on the Atlantic Coast, in January and February; in Honduras in February and March at higher altitudes (700 meters above sea level); in Peten, Guatemala and in most parts of Belize in February and March. Variation in the timing of seed production of up to one month between individual trees in any one stand has been observed.
Gómez and Jasso (1995) carried out a study of the size and form of the fruit of S. macrophylla growing in plantations in Quintana Roo, Mexico. They report a mean weight of 300 grams per fruit; a mean length of 12.5 to 13.0 centimeters; a mean diameter of 5.0 centimeters; and an average of 49 viable seeds per fruit.
Niembro (1996) estimated, in natural conditions, the seed yield based on a study of 108 fruits of S. macrophylla, seeking to understand the existing relations between length, diameter and weight of the fruit and the number of well-developed and malformed seeds in each capsule. The results obtained showed that the fruit of mahogany produce an average of 49 well-developed seeds, of which 39 germinated and gave rise to new plants. The weight and the dimensions of the fruit showed significant, positive correlation with the biological quantity and quality of the seeds produced, at the levels of 1% and 5% of probability. The fruits of greater weight and size are those which are recommended to be collected in order to stock the maximum quantity of viable seeds, according to the evidence offered by the study (Niembro 1996a).
Niembro (1996b), studying the fruit of the Cedrela odorata, obtained an average of 25 seemingly well-developed seeds, of which 15 germinated and gave rise to new plants. The length of the fruit varied between 17.1 to 44.8 millimetres, with a mean of 35.8 millimetres; the weight of fruit ranged from 1.34 to 5.45 grams, with a mean of 3.09 grams.
Whitmore and Hinojosa (1977) studied the seeds of the three species of Swietenia and their hybrids in the laboratory, obtaining the following results:
Table 1. NUMBER OF SEEDS WITHOUT WINGS PER KILOGRAM FOR SPECIES AND HYBRIDS OF SWIETENIA (WHITMORE AND HINOJOSA, 1977)
|Species or Hybrid||Seeds/kg||Seed Origin|
|Swietenia mahagoni||7,840||Virgin Islands (St. Croix)|
|Swietenia humilis||1,540||Guerrero, Mexico|
|S. macrophylla x S. mahagoni||2,880||Virgin Islands (St. Croix)|
|S. humilis x S. mahagoni||1,960||Virgin Islands (St. Croix)|
|S. humilis x S. macrophylla||2,360||Guanacaste, Costa Rica|
The data from the Virgin Islands originate from plantations.
Patiño et al (1983) report on minimum, maximum and average values for the number of seeds per kilogram in S. macrophylla, S. humilis and Cedrela odorata, presented below.
Table 2. NUMBER OF SEEDS PER KILOGRAM FOR SPECIES OF SWIETENIA AND CEDRELA IN MEXICO (PATIÑO ET AL, 1983)
|Species||Minimum Number/kg||Maximum Number/kg||Medium/kg|
Navarro (1995) notes that between 1,300 to 2000 seeds per kg can be obtained in S. macrophylla, giving between 40 to 60 viable seeds per fruit. The author comments that seeds of S. macrophylla can be conserved for one year or more in refrigeration chambers, and for several months in ambient conditions.