Rare breed: The Romanesco Broccoli is prized for its flavour and beauty. Picture: Artichaud

Rebecca’s garden is replete with heirlooms. Different colours, shapes and sizes, they dot the landscape, sparkling like diamonds when the sun catches them at the right angle.

Rouge d’Hiver, Cherokee Purple, Zucchino Rampicante, Little Marvels, Tonda di Paragi… Their very names evoke the exotic, hinting at journeys of discovery in foreign parts.

Indeed, many of them have come from far afield and are highly prized, although call them by the humble names of lettuce, tomato, zucchini, peas or carrots and the uninitiated may think otherwise.

It is the scarcity of these cultivars that makes them so valued, if not valuable in the tradition of diamonds and pearls.

Before the advent of monoculture farming – growing one crop over a wide area – there were thousands of varieties, for example, of apples to be had. Chances are our grandparents could have reeled off dozens without thinking; most of us would be hard pressed to name more than about four or five.

Large-scale commercial farming generally favours hybrid crops that produce a more uniform look, smell and taste, as well as ones that can withstand the rigours of transportation and storage.

Think about the average tomato you buy; it’s either round or oval, big or small. There aren’t too many green, purple, pink or striped ones to be found in most grocers.

Hunting down heirlooms

But there is a band of people around the world dedicated to changing all that, to hunting down and preserving exotic heirlooms so they do not vanish from our lives forever. People who are gardeners and food lovers like Rebecca can go to for a slice or two of tasty treasures.

The Seed Savers Exchange, a non-profit organisation, estimates it has passed on more than a million such seeds to other like-minded gardeners since its inception in 1975.

Founders Diane Ott Whealy and Kent Whealy began their heirloom collection with two plants from Diane’s grandfather – Grandpa Ott’s Morning Glory and German Pink Tomato – that had been brought by his parents from Bavaria to the US in the 1870s.

Heritage Farm, SSE’s headquarters in Decorah, Iowa, boasts 24 acres of certified organic gardens that puts Eden in the shade. There, you’ll find the most diverse public orchard in the United States, a place where 700 varieties of apples from the 19th century are on display; as well as more than 24,000 rare vegetable varieties, including 500 different types of tomatoes and beans, from as far afield as Eastern Europe.

Although there is some debate about what exactly constitutes an heirloom, it is generally held that the plant must be at least 50 years old (some gardeners maintain the plants should have celebrated their 100 birthdays); it must be self-pollinated or open-pollinated (able to reproduce itself); and, like anything worthy of the name, it needs a history worth sharing.

Take the rare Golden Sweet Pea. Collected at a market in India, it is best eaten small and is a delicious addition to stir-fries. It will also look rather gorgeous in your garden, boasting purple flowers and bright yellow pods.

Then there’s the beautiful Romanesco Broccoli. Prized in Italy, its yellow heads look like cascading coral and those who’ve sampled it argue there is no other in the family that can touch it for flavour.

For another splash of colour, try the Purple Peruvian, a potato highly valued in the South American highlands. Regarded by many chefs as the “gem of the Andes”, this not-so-humble-spud raises your average salad a notch and also makes great chips.

SSE and other companies sell heirloom seeds worldwide, so if you can’t find any of the above at the local grocer – and chances are you won’t – you might just be able to grow them yourselves. And discover a whole new meaning of the word treasure.