Brazil nut family (Lecythidaceae) in the New World
The Lecythidaceae are a pantropical family of trees found in the tropics of Central and South America, southeast Asia, and Africa, including Madagascar. The family is divided into three subfamilies, the Planchonioideae, with six genera, the best known of which is Barringtonia, and 59 species in tropical Asia, Malaysia, northern Australia, the Pacific Islands, and Madagascar; the Foetidioideae, with a single genus, Foetidia, and 17 species in Madagascar, Mauritius, and East Africa; and the Lecythidoideae of the Western Hemisphere. This article focuses on the New World species of Lecythidaceae. Two other closely related families, the Napoleonaeaceae and the Scytopetalaceae, were previously considered subfamilies of the Lecythidaceae but they are now treated as closely related families. One South American species, Asteranthos brasiliensis, was at one time placed in the Napoleonaeaceae, but embryological, morphological, and molecular evidence demonstrate that it has a stronger relationship with the Scytopetalaceae.
According to the Angiosperm Phylogeny Group (APG), the Brazil nut family belongs to the order Ericales which is basal to the euasterid clade. Within the Ericales, the position of the Lecythidaceae is not resolved. For more information about this family of tropical trees see The Lecythidaceae Pages.
Species of the Brazil nut family in the New World range from Veracruz, Mexico (Eschweilera mexicana) to Paraguay (Cariniana estrellensis); the Caribbean is home only to Grias cauliflora which occurs in Jamaica and Central America from Belize and Guatemala to northwestern Colombia; and several species of Eschweilera grow in Trinidad and Tobago, but these islands harbor a South American, not a Caribbean, flora.
All species of the Brazil nut family are trees of the under story, canopy, or emergent layers. Among the tallest are the forest-dwelling Cariniana micrantha and Couratari stellata which reach 55 to 60 meters in height. The smallest is Eschweilera nana, a species that often possesses an underground trunk adapting it to survive the frequent fires of savanna vegetation in central Brazil. Trees of the Brazil nut (Bertholletia excelsa) in the 140-150 cm diameter size class have been estimated by radiocarbon dating to be only 270 years old. One of the oldest known trees from the Neotropics, regardless of family, is an individual of Cariniana micrantha radiocarbon dated at 1400 years old.
New World Lecythidaceae are most common and dominant in undisturbed, lowland forests on well drained soils between 19° N and 25° S latitudes. A recent study by Steege et al. reports that the Lecythidaceae and Eschweilera are ecologically the third and the first most important family and genus of trees, respectively, in the Amazon. In a 100-hectare plot established for the study of Lecythidaceae in central Amazonian Brazil, the Brazil nut family accounts for 12% of the individual trees and 6% of the species of trees. The center of diversity and the area with the greatest number of trees of Lecythidaceae is the Amazon Basin. Species of Lecythidaceae also occur in flooded forest, montane forests, and even savanna but in these habitats there are not as many species or individuals as there are in lowland Amazonian forests.
Pollination and Dispersal
The Brazil nut family provides many examples of plant/animal co-evolution. The flowers, fruits, and seeds are adapted to the animals that pollinate their flowers and the animals, wind, and water that disperse their seeds.
Adaptation of Lecythidaceae for pollination has taken place, for the most part, in the male part of the flower. There are two types of flowers, radially and bilaterally symmetrical, and three different rewards offered to pollinators ? fertile pollen, sterile pollen, and nectar. Radially symmetrical flowers, such as those of Gustavia superba (Fig. 1), offer only fertile pollen as a reward; consequently the pollinator reward and the pollen that results in fertilization are morphologically and physiologically identical. Female bees visiting the flowers have no restrictions to entering the flower, collect pollen that is subsequently fed to their larvae, and while they are there pollen is haphazardly deposited on their bodies. When the bees move to a flower of another tree, the pollen is deposited onto the stigma of that flower and eventually causes fertilization. In contrast, species of Lecythidaceae with bilaterally symmetrical flowers, may have two types of rewards, differentiated pollen and nectar.
As an example of adaptations for pollination and dispersal, the pollination and dispersal systems of the sapucaia (Lecythis pisonis), a species native to eastern Amazonian Brazil and Atlantic coastal forests of Brazil , are described.
The sapucaia has bilaterally symmetrical flowers (Fig. 2) that possess both sterile and fertile pollen in the same flower. The fertile pollen is located in a ring at the summit of the ovary and the sterile pollen is found in a hood that departs from one side of the ring and curves over the top of the ovary. Large, female bees, often carpenter bees (Xylocopa spp.), land on the hood to collect sterile pollen from the inside of the hood (Fig. 3). While collecting sterile pollen, the bee receives fertile pollen on the head and back as they brush against the ring. Experiments have demonstrated that the pollen collected by the bee does not germinate while that deposited onto the head and back germinates. It is the fertile pollen that is brushed off the head and back of the bee onto the stigmas of subsequent flowers visited that causes fertilization. For the most part, species of the Brazil nut family have low self-compatibility (pollen from the same tree usually does not result in the production of seeds); thus most fruit set is the result of female bees moving from one tree to another. Only female bees visit the flowers because they are collecting pollen to feed to larval bees. In species with nectar as a reward both female and male bees visit the flowers because they are collecting nectar for their own energy.
The fruit of the sapucaia (Fig. 4) is the largest of all Lecythidaceae. After pollination by bees, the fruits reach the size of a human head after a year of development. The fruit of this species opens via a lid that drops when the seeds are mature. This happens when the fruit is in the tree crown and the seeds are still attached to the inner fruit wall by a cord called a funicle, which, in turn, is surrounded by a fleshy, white outgrow called an aril. Bats (e.g., Phyllostomus hastatus) (Fig. 4) remove the seeds with the attached aril usually on the same night that the fruits open. After the aril is eaten, the bats drop the intact seeds under their roosts.
The woody fruits of Lecythidaceae protect the seeds from predation. But even the thick and woody fruit walls of Cariniana micrantha do not deter brown capuchin monkeys from opening the lids and eating the seeds. The monkeys tear nearly mature fruits from the branches, knock them against the larger limbs and trunk to open the lids, consume seeds, and then drop the fruits containing a few remnant seeds to the ground. In one year, 99.5% of the entire seed production of a tree in central Brazilian Amazon was destroyed by brown capuchins.
The Brazil nut is the economically most important species of Lecythidaceae. Brazil nuts are gathered only from Bertholletia excelsa, a species of non-flooded forest native to Guyana, Surinam, and Amazonian Colombia, Venezuela , Peru , Bolivia, and Brazil . Another species, the cannon-ball tree is cultivated as a botanical curiosity in tropical gardens because of its showy, aromatic flowers and cannon ball like fruits that arise profusely from the main trunk. There are two other species of Couroupita, C. nicaraguarensis and C. subsessilis that are also called cannon ball trees, but these species are not cultivated. Some species, especially in the genus Cariniana, yield valuable timbers.
- Angiosperm Phylogeny Group (APG)
- The Lecythidaceae Pages for descriptions of the pollination and dispersal systems of other species.
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