When early man was evolving as a hunter and food gatherer, he discovered that certain plants store their food reserves in swollenand similar underground structures. The advantage to the plant is that it can survive in this way through either a very cold or a very dry season of the year, and resume growth when the weather becomes warmer or wetter. The human food-gatherers found that if they dug up these they had a handy source of nourishment to see them through a bad time of year, and one that was easily stored. As farming developed, vegetables were cultivated as high-yielding easily-raised crops throughout the world and settlers naturally carried them to new countries. Many are now grown thousands of miles from their first homelands.
When is a root not a root?
Only a minority of root vegetables are true roots in the botanical sense. Carrots, turnips, beetroots and radishes are in fact swollen portions of their plant’s underground root systems. But onions are bulbs, that isof colourless modified for storage of food reserves and the plant’s true root can be seen growing out beneath them. Potatoes, yams and tapioca or cassava are all tubers, that is swollen portions of underground . They have the capacity to send out both roots and shoots after their resting period, so such tubers can be detached and planted in order to establish fresh crops. In contrast, true roots and bulbs are usually raised afresh each year from .
Most root vegetables store the bulk of their nutrients as insoluble starch, a carbohydrate that is readily digested, after conversion into soluble sugar, by man. A few, such as beetroot, have a variable proportion of sugar, and hence are sweet to the taste. Some, such as tapioca, are actuallyif eaten raw, and must be cooked to make them harmless and wholesome. Root vegetables as a whole are a valuable source of essential vitamins, especially vitamin C. They also contribute mineral elements to our diets, but are poor in fats and proteins.
Biennial root crops: radishes, carrots, turnips and beetroots
Many root vegetables have a two-yearly or at least a two-seasonal life cycle, and hence are called. During its first summer the grows, but does not flower. Foodstuffs that might have supported and fruits are diverted instead to the roots, which swell out as they become storage organs. Next spring the plant is able to draw on this reserve, so it can open and ripen profusely early in the season. Therefore its get a good start in competition with other plants and in their struggle against a difficult environment. After seeding, the parent plant dies.
Man intervenes in this simple life cycle by harvesting the swollen roots for his own nourishment, but at the same time he is careful to keep a breeding stock of plants that he allows to mature and bear seed for his next crop.
The familiar red-rooted radish, Raplianus sativus, which matures in a matter of weeks, but will quickly ‘run to seed’ unless uprooted promptly, is a good, if rather high-speed, example of this kind of husbandry. Radishes come originally from the Mediterranean region, where their pattern of short fast growth-periods, followed by pauses of rest, is adapted to short spells of rain under a hot climate.
Carrots are grown on a similar plan; they can, if desired, be stored for several months after harvesting, for their corky skin resists water loss. The wild carrot, Daucus carota, grows on dry chalky soils in southern England, as a feathery-foliaged white-flowered herb. Its thin whitish roots, developed to resist seasonal droughts, bear little flesh, but have an unmistakable carrot flavour.
Turnips, Brassica rapa, and their nearallies the yellow-fleshed swedes, have been grown for centuries as tasty root vegetables, especially for winter use. They are possibly the roots first used by man, for their remains have been found on Neolithic sites. In the eighteenth century a reforming landowner, Viscount Townshend, who inevitably gained the nickname ‘Turnip Townshend’, discovered that they could be grown on a grand scale forraw to sheep and cattle. This enabled farmers to maintain larger stocks through the winter, when grass was scarce. These roots augmented the small supplies of hay, hitherto the only easily-stored winter fodder, and made farms far more productive and profitable. As a rule, turnips are harvested in autumn and stored in clamps which are long stacks covered first with straw, then with a layer of earth, to keep out the frost. In Scotland, sheep are allowed into the fields to eat these roots where they grow.
Wild beetroots, Beta maritima, can be found on European seashores growing as straggly grey-green weeds that resist blazing sunshine on a dry, salty and sandy soil. Under cultivation, growers have developed three strains, all with much larger roots than their wild ancestors. Red round beetroots make tasty sweet table vegetables after cooking. Sugar beets, which are white and tapered in shape, like carrots, are a main source of refined sugar. After this has been washed out at the factory, their spent roots are-used as cattle fodder. Spinach beets are grown for the tenderthat spring from their roots, and are cooked for use as green vegetables, like spinach.
The common onion, Allium cepa, originated in the hot dry climate of the Near East, and its fleshy bulb stores water, as well as food, through prolonged droughts. This explains the presence of several layers of thin waterproof skins surrounding the white modified leaves that compose the bulb. Onions are raised from seed, sown in spring and harvested in autumn as an easily-stored source of both food and flavouring. Those left for seed open ball-shaped clusters of pretty bluish-white flowers on tall stalks, followed by papery white pods holding many small black seeds.
The value of the potato, Solanum tuberosum, as a staple food for man was discovered in prehistoric times, apparently by Inca Indians who lived in highaltitude regions on the slopes of the Andes of Peru, in subtropical latitudes but above the hot levels where the main tropical tubers are cultivated. Potatoes were carried wherever the Incas’ pattern of primitive farming spread. They were introduced to Europe by the first Spanish explorers, and are now grown all over the world. Scores of varieties have been bred, but none is frostproof, and in all cold countries they must be stored away from winter cold, usually in clamps covered with straw and earth.
Potatoes bear pretty white or blue-tinged flowers, with reflexed petals, a prominent central cone of yellow anthers and a green pistil. They ripen many seeds in round green berries shaped like little tomatoes (which are in fact poisonous). But in practice they are only raised from seed by breeders seeking to establish new varieties, becausestart growth slowly and vary in character. The main potato crop is raised by cultivating the land, then burying small tubers, which are called ‘seed potatoes’ (though they are not seeds at all), just below the surface of the soil. Shoots spring up from little buds, called ‘eyes’, on the surface of the tuber, and roots break out at the same places. A dense low bushy plant results. This sends out, just below ground level, odd white side stalks, on each of which a new tuber develops, close to the soil surface. About midsummer the farmer ‘earths-up’ his crop, using a special plough to pile soil over these new tubers, which would otherwise become hard, greenish-brown, badly-flavoured and slightly poisonous; then in autumn, when the foliage has withered, he uses another plough, or machine, to raise his heavy underground crop. Similar practices are followed in gardens.
Tapioca is obtained from the cassava or manio’c plant, Manihot esculenta, native to Central and South America, but now grown in every tropical country, especially West Africa and Southeast Asia. It is planted as, on well-cultivated and fertilized land, and takes 12-15 months to mature. Its jointed shoots quickly grow tall, often exceeding 2m (6.5ft), and the crop looks like a forest of waving stems bearing large compound leaves. Clusters of long sausage-shaped roots develop below ground, giving a heavy yield of over 30 tonnes per hectare. These starchy roots hold small amounts of poisonous prussic acid and cannot be eaten raw. American Indians prepare them for food in two ways, either slicing and boiling them to wash out the poison, or drying them and then pounding them into a coarse meal called manioc. The familiar tapioca used for puddings is prepared for storage, or export from tropical countries, by an elaborate factory process of rasping the roots, washing out the starch grains, then drying them to form a meal. This is next rocked in hammocks, causing the grains to form round globes, which are cooked gently to make them hold together. The waste is fed to pigs.
Yams, which are a staple food in tropical Africa and the West Indies, are the large tubers of a climbing plant called Dioscorea batatas, originally native to China, and its allied species. Yams are planted as tubers which produce slender stems that are trained up stakes. After about 10-months growth their bluntended tubers (often 40cm (i6in) long by 10cm (4m) thick), mature and are dug up. The yams are stored in racks, with air circulating round them; as long as they are kept dry they will not sprout again. They have a food value comparable to that of potatoes, holding about four-fifths by weight of water and one-fifth nutritious starch, with a little protein.
Taro, Colocasia esculenta, the staple root crop of the Pacific Islands, is also grown in the West Indies under the names of eddoes and cocoes. It is a monocotyledon related to the arum lily, and grows as a tuft of tall stalks bearing huge heart-shaped leaves. Its oval roots yield the starch that is made, in Polynesia, into a thin porridge called ‘poi’.
A number of other tropical plants produce edible roots, including the sweet potato (a morning glory relation); uca (a wood sorrel relation); ulluco (of the family Basellaceae); and arrowroot (related to the marantas, popular as houseplants).