Without being ‘food for free’ fanatics, many people have experienced the delightful flavours on offer to those who glean wild blackberries, raspberries or strawberries from the countryside. With species like these it is easy to see what attracted our ancestors to bring them into cultivation. In other cases however, one is left to wonder, how did anyone ever think of eating that? Such a crop is the cashew nut, which is a relative of the poison ivy, poison oak and the poison sumac.
The cashew is a tropical tree, which can grow to a height of 15 meters, it is a native of Brazil, but was already widely grown throughout South America and the Caribbean before the arrival of the Europeans. The Latin name of the cashew, Anacardium which means ‘shaped like a heart’ describes the kidney shaped nut which hangs below the bright red or yellow cashew apple (strange that). Sink your teeth into a cashew nut as it falls ripe from the tree and you quickly discover that the thick shell, which surrounds the nut, is full of toxic oil that not only tastes disgusting but also blisters your mouth. Extracting the nut without contaminating it with this noxious substance is a complex process that may involve soaking it in hot water to volatilise the oil or burning it off by gentle roasting. Cashew yields are low with trees being prone to more than a hundred different pests and diseases, this can result in less than thirty or forty nuts being produced per tree, no wonder they cost a packet.
It must surely have been the cashew apple rather than its nut, which first attracted man to the tree. The cashew apple is a delicacy almost unheard of outside the tropics. It is a false fruit, which is formed from the swollen stem, which supports the cashew nut. Similar to a pear in both shape and size, the cashew apple tastes rather like eating a sponge soaked in an astringent sugar solution. It is no great surprise that about 95 percent of the world’s cashew apples are left to rot in the orchard. Fruit eating bats may disagree, as they are the main seed dispersal agents of the cashew, and they just love them! In Brazil cashew apples are used to manufacture a soft drink, in the Caribbean and parts of West Africa they are fermented to produce cashew wine, while in Goa in India they go one better and drink cashew apple brandy. It is considered by many to taste as good a real brandy, and it certainly tastes better than the liquid extracted from the shell of the cashew nut, which is used commercially in brake linings!
The cashew has a rather interesting sex-life, in that a single tree will initially produce flowers that are entirely male, and only later in the season will it produce flowers that are hermaphrodite or occasionally female. If the male flowers are to avoid sexual frustration it requires that there is some overlap in the stage of flowering between different trees. This is a trick that the pistachio, (a relative of the cashew) is amazingly poor at.
The pistachio is a tree of similar stature to the cashew, but it is a native of the Old World rather than the new. Unlike the cashew, individual pistachio trees are either entirely male or entirely female. The sex-life of the pistachio is remarkable because although individual trees may be as old as 700 years, they frequently have the sexual competence of a novice. Put crudely, the problem is a simple failure to get their act to together. The most widely grown male trees known as ‘Peters’ have an unfortunate habit of blossoming too soon to satisfy the female ‘ Kerman’ trees. Other pistachio males have even greater impotency problems than do Peters, in that they are only sexually active for a couple of days each year. Peters usually manage to sustain flowering for as much as three weeks, which is sufficient in most years to allow an overlap with the females of two frantic days for wind pollination to occur. Unfortunately all too frequently male and female pistachios fail completely to synchronise their flowering and no nuts are produced, a problem that appears particularly acute in the United States. Even when the two sexes do hit it off, pistachios only crop well every alternate year, the reason for these ‘on’ and ‘off’ years remains uncertain.
Humans have been growing and consuming pistachio nuts since antiquity, they are mentioned in the Old Testament story of Joseph. The Queen of Sheba was especially fond of them, with the assistance of a few of her court favourites, she is said to have eaten the entire pistachio crop of Assyria. Pistachio nuts remain a favourite food in the Middle East to this day, where they form an essential ingredient of wedding feasts.
Given the fact that the crop has such an ancient history of cultivation, it is remarkable that its inability to synchronise male and female flowering has not been addressed. The explanation for this may be related to female infidelity. In its native Middle East, when male pistachios fail to perform, closely related wild trees that grow in proximity to the orchards are often able to pollinate the female trees. Nut production is assured, and there is therefore little reason to select for delayed flowering males or early flowering females. When pistachio cultivation became popular in the southern United States as the result of a tax evasion scam and the banning of pistachio imports from Ayatollah Khomeni’s Iran, the American female pistachios were unable to turn to their wild relatives in their times of need. When no alternative pollen source is available, the mistiming of male and female flowering inevitably results in total crop failure. Any delight felt by the Ayatollah at the impotence of the American Peters must surely have been matched by the embarrassment caused by his unfaithful Iranian females.