Another Life:The natural history of Christmas dealt here last December with the botany and biogeography of the spices in an average wedge of pudding. But it can penetrate even further into the rainforest and other tropical habitats on the trail of our festive nuts.
Few of them, perhaps, seem quite so exotic since muesli went upmarket: I am still a bit amazed to be chewing on chunks of Brazil nut for breakfast, remembering them still in their shells, a once-a-year, tooth-threatening treasure in the toe of my Christmas stocking.
Brazil nuts (Bertholletia excelsior) present, as it happens, a great ecological story - one to make you wonder how they can possibly be so plentiful as one of the luxury nuts of the western world.
For a start, they are almost all still harvested from wild-growing native trees in the remaining rainforests of Amazonia - towering, often ancient, trees in stands of 50 to 100, mixed in with other natural vegetation in the drier forest areas of the Guianas, Colombia, Venezuela, Peru, Bolivia and Brazil.Bertholletia is a unique species and depends on an ecosystem that has so far defied artificial and economically successful replication in plantations, either in Amazonia or elsewhere in the tropics.
Brazil nuts begin as spires of creamy "snapdragon" flowers blooming high in the canopy. Pollination largely depends on forceful, solitary bees, native to undisturbed rainforest, with long tongues made to take nectar from the tree orchids of the forest. The fruit of Bertholletia grow as woody spheres the size of a large grapefruit and weighing up to 2.5k, that fall with a thud in the rainy months of January and February.
The nuts are packed inside this capsule, perhaps 20 of them or more, and are liberated naturally by the chisel-teeth of rodents - agoutis and squirrels - who eat some and cache others, forgetting where they put them sufficiently often to guarantee that some nuts start growing a year or so later.
The human harvest, with machetes, is by the forest families living in reserves who load the nuts onto rafts or canoes and paddle them to the traders in the Amazon's river ports. In 1986 (such figures are rare), more than $5 million (€3.8) worth of nuts were exported through Manaos alone.
Brazil nuts, you will be startled to read, are naturally radioactive, extracting radium and barium from the soil. It's not enough to start a Geiger counter clicking or be useful to Russian assassins, but with beta and alpha radium activity "significantly above" the natural background level.
Most of it is not retained by the body, but a whole box of chocolate brazils on Christmas evening may send you to bed with a certain glow.
While generally full of proteins, fats, vitamins and healthy amino acids, nuts can also concentrate some of nature's more powerful chemicals and allergens, not to mention - if badly stored - dangerously toxic moulds.
You will know about the prussic acid of bitter almonds (absent from the sweeter sort we eat). There's also a caustic resin, with daunting industrial uses, that has to be removed in producing cashews, one of my favourite nibbles.
The cashew tree, Anacardium occidentale, is a small but wide-spreading tropical evergreen that grows in sandy soils across the tropics, from its native north-east Brazil to the Indian and Vietnamese plantations that now lead world production.
Each cashew is held in a kidney-shaped shell that appears stuck on the tip of a soft and pear-shaped "apple", a sort of pseudo-fruit with an acidic pulp that can be eaten or fermented into liquor. The appended cashew shell, on the other hand, contains within its woody cells a caustic substance called urushiol, which has to be removed by roasting or steaming. Shelling by machine is difficult, and painful rashes are common among poorly-paid women workers in India, shelling by hand with wooden mallets and bits of bent wire at a rate of about 200 nuts per hour (didn't mean to spoil your party).
Pistachio nuts (Pistacia vera), on the other hand, with their distinctive pale-green kernels, have been thoroughly industrialised since a US plant scientist bred a modern variety called Kerman from wild nuts brought home from Iran. Growing in grape-like clusters, the shells split open themselves with an audible pop, whereupon, in Californian orchards, they are mechanically shaken from the tree - in one minute! - and rushed off to be dried, hulled and salted.
The trees of Iran, Turkey and Syria, however, still supply the bulk of the world's pistachio trade.
The sweet and buttery pecan (Carya illinoinensis), is thoroughly American, ripening on the tallest kind of hickory tree in the heat and humidity of the south-eastern states. It was made the state tree of Texas 60 years ago, and grows abundantly on the ranch of President Bush, who served pecan pie to President Putin.