Until yesterday I was under the happy illusion that I knew a thing or two about fruit. Not any kind of expert, you understand, just reasonably well-versed in the shape and taste of some of nature's bounty.

Fruit has increased in variety as I've grown older; there is almost a perfect correlation. When I was tiny and living in England, apples and pears were fruit - anything else was virtually unavailable. Then oranges and bananas made a big comeback in the fifties. Gradually, like a geometric progression, the rate of increasing variety accelerated inexorably. Grapefruit arrived; so exotic were they that restaurants felt no need to do anything with them other than cut them in half and put a glazed cherry in the middle.

Remember the coming of kiwis? Suddenly no plate was complete without a fan of thinly sliced kiwi for decoration. And that was the start of a whole new idea: exotic fruit as decoration for a plate.

Recently as the choice has been getting wider and wider I've added papaya, passion fruit and mango to my vocabulary. But passably adventurous as I am, nothing had quite prepared me for the array of exotica that confronted me in the fruit and vegetable department of Quinnsworth's Merrion Centre.

There are things on display there that make you wonder what exactly nature was thinking of when she designed these offerings. Small, bulbous things called mangosteens with a thick skin that needed a cleaver to split, spiky melons which are clearly designed to give the message 'don't touch', and then there's the cassava root. Looking like the proverbial baby's arm holding a tangerine, this brown, hard, hairy brute made me consider the bravery of the first person to look at one and think 'I must give this a taste.' Quite the oddest of all is the eddoe, the size and shape of a small onion, with a skin like a pangolin. This is one fruit that is definitely more for decoration than food.

Enter Freda Molamphy, Quinnsworth's expert. She knows more about exotic fruit and vegetables than any member of the human race I've ever met. She even knows recipes that include this arcana of the vegetable kingdom. She introduces me to the array of bizarre creation displayed on the shelves. 'Mangoes and papayas are still the most in demand. Use them in fruit salads, or slices of papaya with Parma ham as a starter. Mango sorbet or cheesecake is beautiful.' She shows me a custard apple. This looks a bit like an artichoke with the leaves shaved smoothly off, which has a soft, smooth flesh that I really liked. 'I make ice-cream with these.' Freda tells me. I said hello to chow-chows, rambutans, granadillas and Sharon fruit.

This last took me by surprise. Sharon fruits or Persimmons are also known here, it seems, by their Italian name: cachi. They grow in the orchard of my old family house in Italy, and I'd never seen them anywhere else until now. I've never been crazy about the taste of them, but it warmed my heart to see a little piece of Italy in Merrion. They even had that other common southern Italian fruit, the prickly pear.

Freda and I discuss the uses of some of the pulpier exotica with the peculiar shapes and huge seeds. 'Could it be,' I ask, 'that some of these might be better employed sprayed gold and hung on a Christmas tree, rather than forming part of our diet?' She agrees. 'Some of these tropical fruits have a pulpy interior rather than a fleshy one. They really are just for decoration.' Then we come to the Chinese lanterns or physallis. These are gloriously perfumed little berries, sweet and intensely flavoured that were serious contenders with the custard apple for my favourite fruit of the day.

An equally unusual assortment of vegetables are here. Yams, cassava root, chayote, organic celeriac and salsify, lamb's lettuce and the green from hell, sorrel. Freda tells me that sorrel is becoming one of their best-sellers - quite the flavour of the moment; presumably among those with a highly developed sense of fashion and no taste buds.

Anyone with a penchant for the unusual and an adventurous palate no longer has an excuse for not satisfying themselves. Global trade has even removed the exigencies of the seasons; practically any vegetable produce can now be bought at any time of year. I'm yet to be convinced that this is necessarily a good thing, but it's a fact, and it's visible on the shelves.

A thought strikes me; these exotic fruits are not cheap, presumably because transport, storage and small demand make economies of scale impossible. Yet in the countries from which they come they probably have little value. The clear plastic tray that held two Thai mangosteens would probably be worth more in rural Thailand than half a dozen fruits - a peculiarity inherent in the workings of the global economy.