Posted by: David Green | December 21, 2009

Christmas Nuts

I guess there are more nuts in the shops at Christmas than at any other time of year… One of my favourites is the Brazil. Brazil nuts are one of the few crops that are harvested exclusively from natural rainforest. They are the fruit of the tree, Bertholletia excelsa, which reaches 45 m tall and is native to the Amazon basin. On the tree, the ‘nuts’ are packed like the segments of a Terry’s chocolate orange, into a shell. The fruiting season can be quite hazardous; imagine a hard, fist-sized object dropping from a ten-storey tower block!

Brazil 'nuts' in a hard fist-sized shell from the museum collection

The genus Bertholletia, of which the Brazil nut is the sole representative, is named in honour of the French chemist Claude Louis Berthollet. This is oddly appropriate as the tree has a remarkable ability to concentrate certain chemical elements. Brazil nuts can contain extraordinary quantities of selenium, a mineral which is essential (in small amounts) to human health.

Brazil nut trees only crop in natural rainforests. They are the basis of an export industry that provides employment for thousands of people, and as a result they are strong incentive for conservation in some areas. Recent research has shown that the flowers require a particular species of bee for pollination. The bees in their turn depend on an orchid if they are to survive (since the male bees use the orchid’s fragrance to attract females). The orchids are absent from forests that are damaged by logging and so are viable nut trees… Another interesting relationship is with the Agouti, a rodent which is one of the few animals that can break open the fruits. In times of plenty, Agouti’s bury nuts in much the same way as squirrels. They forget where some of them are and these provide the next generation of nut trees. A short film of this behaviour can be found on the BBC website.

The edible part of the nut is the oily endosperm, rich in selenium. If you scratch a table this Christmas try rubbing it with a 'nut', the scratch will disappear!

David Green
Curator of Mineralogy

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