Taxonomy and Distribution

• Title

  Taxonomy and Distribution

• Authors

  Scott Alan Mori

• Description

  Bertholletia excelsa belongs to a pantropical family of trees (Lecythidaceae) that includes approximately 200 species in the Neotropics, distributed from southern Mexico into southern Brazil (Mori and Prance, 1990a; Prance and Mori, 1979). The Brazil nut represents a single species in the well-defined genus Bertholletia. Although there is considerable variation in fruit size and shape and number of seeds per fruit, there is no justification for recognizing more than one species of Bertholletia. The closest relatives of B. excelsa are among species of Lecythis commonly referred to in the vernacular as the jarana group (Mori and Prance, 1990b). Other species with edible seeds in the family are Lecythis pisonis and its relatives, L. minor and L. ollaria. The latter two species, however, sometimes cause hair and fingernail loss because of excess selenium accumulation in the seeds (Dickson, 1969; Kerdel-Vegas, 1966). Nevertheless, the differences between Bertholletia and Lecythis are so great that there is little hope for introducing genetic material from one genus into the other via hybridization. Consequently, germ plasm for improvement of Brazil nut production will have to come from the variation found within B. excelsa, not from closely related species in other genera. Bertholletia excelsa is an Amazonian plant that prefers nonflooded forest (terra firma) in the Guianas, Colombia, Venezuela, Peru, Bolivia and Brazil. The climatic conditions under which Brazil nuts grow are summarized in de Almeida (1963), Diniz and Bastos (1974), and Mori and Prance (1990b). Brazil nuts are cultivated in tropical botanical gardens far outside its native range, and minor plantations have been established in Kuala Lumpur in Malaysia (Müller, 1981) and Ghana in Africa (D.K. Abbiw, pers. comm.). Trees of Bertholletia excelsa occur in stands of 50 to 100 individuals that are known as "manchales" in Peru (Sánchez, 1973) and "castanhais" in Brazil (Dias, 1959). Density of Brazil nut trees per hectare varies considerably throughout the Amazon. In a study of Brazil nut production in eastern Brazil, Miller (1990) found from 9 to 26 reproductive trees per hectare, while Becker and Mori (unpublished data) found only one tree over 10 centimeters dbh in a 100-hectare plot in central Amazonian Brazil. There is some evidence that Brazil nut trees are gap dependent (Mori and Prance, 1990b). Moreover some authors have suggested that stands of the Brazil nut owe their origin to pre-Colombian Indians (Miller, 1990; Mori and Prance, 1990b; Müller et al., 1980). An understanding of the development of reproductive individuals from seed is still needed before management of Brazil nuts in natural stands is possible.