Tubers

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TUBERS

TUBERS. Tuber is a loan word deriving from the Latin verb tumere (to swell). It was introduced into colloquial English via botanical Latin during the Renaissance and retains a number of related meanings: a swelling, a growth resembling a knot, or even a truffle. When applied to vegetables, tuber is now understood to mean a fleshy underground swelling on root strands that normally contains varying proportions of starch. In reality, this definition is quite imprecise given the huge diversity of tuberous-like roots and stems that exist in nature.

For example, taro (Colocasia sp. ), is sometimes referred to as a tuber and sometimes as a corm since it straddles the definition of both. Other vegetables, like the arracacha (Arracacha xanthorrhiza ) of South America, are often classified as "tuberous rooted" since the swollen part is not distinctly separate from the crown or herbaceous (above-ground) parts of the plant. The potato is considered a classic example of a common tuber, since the swollen part forms along various root strands and is only connected to the rest of the plant in this fashion. However, it is possible to induce this feature in any number of wild tuberous-rooted plants once domesticated and carefully selected.

Most true tubers are capable of reproducing themselves vegetatively and when reproduced in this manner, they become true genetic clones of their parents. This reproduction technique allows beneficial characteristics, such as flavor, texture, storing qualities, or resistance to certain pests and diseases to be preserved from one generation to the next. It would appear, however, that most tubers originally appealed to humans for their starch or sugars, especially tubers that could be consumed raw. Only later did cookery expand the list of choices, since many tubers like cassava are toxic until exposed to heat or some other processing step.

Nutrient rich and relatively easy to gather, tubers have played a major role in the history of human diet, since they could be collected from the wild and stockpiled against times of food shortage. This dietary shift from happenstance to organized gathering, which required calculations regarding collection, storage, and distribution, brought about profound changes in human social organization and development, even more so after tubers were brought under cultivation.

Pre-agricultural societies relied heavily on foraged tubers, especially those that required little or no processing. Bog potatoes or groundnuts (Apios tuberosa ) supplied the hunter-gatherers of eastern North America with an easy to collect source of small, starchy tubers that could be stored in pits for later use and eaten like nuts. Even for societies that later turned to intensive agriculture, such wild tubers remained an important supplement to the diet. However, many tuberous vegetables like the water parsley (Oenanthe sarmentosa ) and wood sunflower (Helianthus strumosus ) of North America, the bagana (Amorphophallus abyssinicus ) of Ethiopia, and the kudzu (Pueraria lobata ) of New Guinea, were never brought under cultivation by the native peoples of those areas, but simply gathered from the wild and traded, or allowed to grow in patches kept free of competing weeds. These managed plants were the preliminary steps toward gardening and primitive agriculture.

There is no precise record of when the first tubers were brought under cultivation on an organized basis, but in all likelihood the taros of India (if we allow that Colocasia and Alocasia are tubers) were among the first since they are mentioned in Sanskrit sources and terms for them are known in pre-Sanskrit languages. Doubtless they were followed or even preceded by potatoes in the high Andes, the yam bean (Pachyrrhizus erosus ) in Central America, and the chufa (Cyperus esculentus ) of the Mediterranean region. Vestiges of many tuberous plants have been found in caves, but this does not mean they were cultivated. Unless there are corroborating written records, or artifacts depicting tuberous vegetables, archeology cannot safely establish that a tuber was in fact cultivated since traces of pollen, preserved seeds, or actual dried tubers can originate from wild as well as cultivated sources. Furthermore, even where there are physical depictions of the plant, as in the case of chufa and coco grass (Cyperus rotundus ) in ancient Egyptian paintings of pleasure gardens, this only proves that they were appreciated as ornamentals.

Yet, over time, many tuberous vegetables were indeed brought under cultivation in order to increase the supply and the reliability of the harvest. The highest percentage of indigenous cultivated tubers of different species is found in South America, where there is presently a concerted attempt to analyze and promote their uses. Elsewhere, many tubers gathered from the wild have fallen into neglect even where this nutritional diversity supplied a more balanced diet. Additionally, except for the Pacific islands, almost all of the lesser sorts of cultivated yam, such as the White Yam (Dioscorea rotundata ), and the Buck Yam (Dioscorea pentaphylla ), have decreased in production because of the introduction of commercially improved sweet potatoes. No tubers have done more than the potato and sweet potato (Ipomoea batatas ) to alter human agriculture and diet, since both of these plants can be grown in a wide variety of soils and microclimates on a large commercial scale.

In the tropics, however, taros and yams (Discorea sp. ) remain key food crops, followed by the New World cassava (Manihot esculenta ) and to a limited extent malanga or yautia (Xanthosoma sp.). Consumption patterns vary from country to country and from one cultural group to the next, and practical growing considerations should not be overlooked. For example, in some areas, cassava and malanga have become important agricultural supplements since they will grow where taro will not and like sweet potatoes, they yield a ready supply of nutritionally rich greens. Since the 1500s, Old and New World tubers have moved out of their original habitats to such an extent that there is often a great deal of confusion as to where the plants came from. The inventory that follows deals with tubers based on their continent of origin, but with brief comments on how they have spread to other parts of the world, or how they are employed in local cuisines.

Africa (Sub-Sahara)

When we consider that yams, taros, sweet potatoes, and cassava are all exotics introduced from other continents, the range of indigenous tuberous vegetables available to Africans is extremely small. The African landscape is rich in leafy vegetables, but until the introduction of yams about 1000 C.E., there was no large tuberous vegetable serving as a staple on a continent-wide scale. Only here and there, locally occurring tubers provided limited food supplies for those willing to gather them. Most of Africa's indigenous tubers are small in size and few of them have ever been brought under cultivation. Furthermore, to date, there are no complete continent-wide inventories of native tuberous plants, a task made doubly difficult because of so many common synonyms that exist in the numerous languages of Africa, not to mention the political instability in several key countries.

While there has been a large amount of research devoted to African foodways and tribal cultures, little has been devoted to traditional gardening. The growing, gathering, and cooking of traditional plants is largely a woman's task in Africa, and in the past, this has been treated as an activity of low status. Fortunately, there is now a shift of interest in promoting the conservation and use of underutilized and neglected foods, particularly in Botswana, Ethiopia, Kenya, and Nigeria.

Many of the native tubers listed below are presently being inventoried for study and evaluation for possible breeding programs in conjunction with sustainable agriculture. However, very few of them are mentioned in cookbooks. Aside from these, Arisaema schimperianum, Campanula edulis, Commelina benghalensis and latifolia, Cyperus esculentus, Dioscorea quartiniana, and Dioscorea schimperiana all provide a source of indigenous tubers that are collected from the wild in several parts of Africa.

African yam bean (Sphenostylis stenocarpa). This plant produces protein-rich seeds, edible leaves, and a large spindle-shaped tuber that can be cooked like a potato. The yam bean is mostly consumed by villagers in West Africa and even appears in cookbooks from that region.

Anchote (Coccinia abyssinica). This perennial occurs as a wild vine in several parts of East Africa. The small tubers are cooked like potatoes in Ethiopia. Coccinia grandis and Coccinia triloba, both relatives of anchote, are gathered by some tribes in Kenya.

Hausa potato (Solenostemon rotundifolius). Formerly classified Coleus rotundifolius, these black tubers are prepared like potatoes and may be eaten either raw or cooked. This plant has been introduced into Southeast Asia, where it is employed in curries or eaten with coconuts.

Jacob's Coat or Sayabana (Coleus blumei). Both the leaves and tubers are eaten. The leaves are also added to fermented beverages. Now introduced into tropical Asia.

Livingstone potato (Coleus parviflorus). Also known as the country potato and African potato, this handsome tuber is widely cultivated in the dry regions of East and West Africa. The tubers resemble the crosnes of east Asia, but have yellow skin and white flesh. They are also dried and then ground to make a flour for dumplings. The Arabs are thought to have introduced this into India. From there the Portuguese introduced it into Malaysia and Indonesia.

Serendipity berry (Dioscoreophyllum cumminsii). Known as utobili in Nigeria, this shrub produces a number of products useful to the native peoples of West Africa. The tubers are employed in soups, especially as thickeners and are considered one of the distinctive ingredients in regional Nigerian cookery.

Eurasia (Including the Mediterranean Basin and Pacific Islands)

The Eurasian land mass represents a huge diversity of tuberous plants, and some of the earliest ones brought into cultivation. This includes all the cultivated taros (two species each of Alocasia and Colocasia, one species of Cyrtosperma ), most of the agricultural yams (roughly ten species out of 600), and innumerable lesser tubers such as the kudzu (Pueraria lobata ), which has become an invasive pest in the southern part of the United States. Historical information on many of the tubers from this part of the world is good, since their cultivation is often noted in the records left by peoples residing in ancient China, India, the Near East and Mediterranean Basin. It should be noted, however, that most of the Eurasian staple tubers are of tropical origin.

Adder's grass (Dactylorhiza maculata). This is technically an orchid whose tuber was ground to yield a starchy powder employed in the preparation of salep. Salep, a word of Turkish and ultimately of Arabic origin, was a beverage served cold during hot weather and hot during cold weather. The actual drink is of Byzantine origin (or perhaps even Lydian as some historians have suggested), since the orchid tubers with which it is made are found primarily in Asia Minor and Armenia. The starch was also used to thicken milk and more recently to make a line of elastic ice creams popular in the Middle East.

Historically, salep was also popular in seventeenth-and eighteenth-century England and America, especially in coffeehouses, but in general it was regarded as a health drink. It was also thought to contain aphrodisiac qualities. It has been replaced by cornstarch or arrowroot.

Asphodel (Asphodeline lutea). A native of the Mediterranean, the Egyptians, Greeks, and Romans prepared it like a potato. It prefers sandy soil and was probably a minor crop in some parts of North Africa during classical antiquity. It also yields a starch that was highly valued as a food thickener for making medieval blancmanges, sauces, and thickened soups.

Chufa (Cyperus esculentus). Chufa is found throughout the Mediterranean Basin and in parts of sub-Saharan Africa. It has been taken to most parts of the world where it is either maintained as a garden plant or has managed to escape into the wild (as in the case of North America). Wild chufa, which is often called nut grass in English speaking countries, produces small tubers resembling brown shriveled peas. Their flavor is similar to almonds and when pressed, they yield an oil similar to almond milk. The tubers of cultivated chufa are much larger, sometimes the size of a lima bean, and much easier to employ in cookery.

Chufa was domesticated thousands of years ago and was probably an important food source for the ancient Phoenicians. The Egyptians grew it both for its ornamental leaves and its tubers. The Byzantine Greeks used it both in cookery and medicine. It is still employed in modern Spain in the preparation of horchata, a milky beverage popular in the fall. The British Isle imitation was called orgeat in eighteenth century cookbooks.

Crosnes (Stachys affinis). Generally harvested during the winter months when the tops are dead, the tubers are knobby and white. The plant resembles nettle and prefers moist, shady soil; thus, it is ideal for marginal ground. It is also extremely hardy, and has been cultivated as an important supplement crop in China and Japan for many centuries. The tubers are pickled or eaten in stir-fries. The plant was introduced into France in the 1880s and takes its European name from the village of Crosnes (Seine-et-Oise), the site of a large experimental farm where crosnes were first trialled. Crosnes are also grown in the United States and are now commonly seen in farm markets.

Devil's tongue (Amorphophallus rivieri). A native of Southeast Asia that is now very important in Japanese and Korean cooking, the tubers yield a starch that is solidified into a gel called konnyaku (yam cake). Noodles called shirataki are made from this. Yam cake is also commonly added to Korean hot-pot dishes.

Elephant's foot or telinga potato (Amorphophallus campanulatus). Mentioned in Sanskrit, this is one of the most ancient cultivated plants of tropical Asia. In India, the tuber (also called a corm) is prepared in curries, fried, added to stews, and cooked in syrup. It is also sold in cans and is imported in this form to the United States. The plant is now cultivated in East Africa, especially in areas where Indians have settled.

Giant swamp taro (Cyrtosperma camissonis). A native of the Pacific Islands and Indonesia. It grows well on the difficult soils of coral atolls, thus it is much favored by Polynesians. The tuber requires several years to mature, so cultivation is continuous, with some being dug while others are being planted.

Kembang Bangké (Amorphophallus variabilis). A near relative of devil's tongue mentioned above, this is also used to make the starchy gel known as konnyaku.

Korean bellflower root (Platycodon grandiflorus). This is the east Asian counterpart of the European rampion. Called toraji in Korean, is it employed in stir-fries and kimchee, or pickled like crosnes.

Kudzu (Pueraria lobata). Kudzu originates in China and Japan, and its common name is of Japanese origin. It grows wild in the grasslands of the Pacific Islands, and because all parts of the plant are edible, it was formerly important in the agriculture of India, Malaysia, and Southeast Asia. Because the tubers, which can reach a length of three feet (1 meter) require several years to mature, the plant is slowly losing ground to sweet potatoes as a staple even though the tubers contain roughly 27 percent starch. The vines grow anywhere from 24 (8 meters) to 36 feet (12 meters) in one season and will overwhelm any plants nearby.

Polynesian Arrowroot or Tacca (Tacca leontopetaloides). Grown mostly on the Pacific Islands, this is an ancient source of starch, which has long been sold under the name of pia flour. The plant is cultivated throughout Oceania as well as in India and Sri Lanka. Cultivation is now declining in favor of cassava, which is easier to grow.

Rampion (Campanula rapunculus). The tubers resemble tiny potatoes and were once popular in salads and as a table vegetable. It is still cultivated to some extent in France, Germany, and Switzerland. Historically, it was grown as a garden vegetable even during Roman times, with the center of cultivation in the Rhine Valley. Its Latin name means little turnip, and it was evidently an important food among the Gauls and early Germans, perhaps with some now lost sacred connections. Numerous folk legends survive dealing with personifications of this tuber, including the famous Grimm fairy tale about Rapunzel, and the story of the first king and queen of ancient Polandthe queen's name was rampion.

Soldier orchid (Orchis militaris). Found in temperate regions of Europe and Asia, this tuber was often gathered and prepared like a small potato. It was also used in medicine and in the preparation of salep (see adder's grass). Because the tubers resemble testicles, they were thought to enhance male sexuality. As the common name implies, the tuber was often employed as a forage food by armies on the move.

Taro (Colocasia sp. ). This group of tubers includes two cultivated species as well as the closely related genus Alocasia, all of which appear to originate in southern India. Some Indian historians claim that taro was brought under cultivation over 10,000 years ago, although this is not firmly established. Whatever the date, it is clear that taro is one of the most ancient of the cultivated Old World tubers. It spread to Egypt by the first century C.E. and then to many parts of the Mediterranean. The Spanish and Portuguese brought it to the New World. The history of taro and its many forms is taken up in further detail below.

Yam (Dioscorea sp. ). Yam is a loose term covering some 600 species, of which about ten are cultivated for food. Many member of this genus are poisonous or require processing to remove toxins in order to make them safe for consumption. The common name derives from a West African word nyami, but the botanical origin is thought to be Sri Lanka or Southeast Asia. Since this is such a large and economically important group, yams are treated separately below. Yams are now found in tropical regions throughout the world.

North America (United States and Canada)

In terms of naturally occurring and domesticated native tubers, North American biodiversity is relatively sparse. Most of the edible tuberous plants that exist here were employed by native populations prior to European contact. Very few of these plants were acculturated by Europeans except under frontier conditions or during times of scarcity. The introduction of the sweet potato in the South and the potato in cooler parts of the continent more or less preempted the domestication of potentially important native tuber crops that might offer nutritional alternatives better adapted to soil and climate. Only the Jerusalem artichoke (Helianthus tuberosus ) has played a minor role doubtless because of its similarity to the potato when cooked. The following list is by no means complete, but it does list the primary tubers known to native peoples.

Arrowhead (Sagittaria sagittifolia). Found all over continental United States and Canada, it is known by many Indian names, the most common being wapatoo. The tuber tastes like a potato and can be sun-dried for use in the winter. A closely related species, sessile-fruited arrowhead (Sagittaria rigida ) is found only in the eastern North America. Both plants are aquatic. It is also important to note here that European and Asian arrowhead, formerly treated as separate species, are now grouped together, thus this plant is in fact found throughout the Northern Hemisphere.

Bush morning glory (Ipomoea leptophylla). A native of the Great Plains, this was once collected for its tuber, which resembles a sweet potato. The tuber has also been classified as a root, although the distinction here is hazy. Some plants produce unpleasantly bitter or tough tubers, while others are starchy or even pleasantly sweet. These differences may be environmental. The tuber may be eaten raw or cooked and is excellent when sliced and sun-dried.

Groundnut or bog potato (Apios americana). Sweet and starchy, these small tubers contain about 17 percent crude protein and are therefore among the most nutrient rich of all the New World tubers, more so even than the potato. They can be eaten raw or prepared like potatoes, or added to soups and stews like beans or peas. There is considerable breeding being undertaken to develop commercially feasible crops, with over ten named cultivars in circulation among experimental growers at the present time. The commercial advantage of this tuber is that it can be grown on marginal land and it is not subject to a large number of pests.

Jerusalem artichoke (Helianthus tuberosus). First noted by Europeans about 1605, the Jerusalem artichoke has experienced numerous cycles in popularity over the ensuing centuries. It was promoted by French agricultural writers Antoine Parmentier (1789) and especially by Victor Yvart (1790) who wrote a treatise on the subject, and is even mentioned by American cookbook author Amelia Simmons in 1796. Rich in inulin, the Jerusalem artichoke was widely cultivated by native peoples in North America, especially in the Midwest where it is thought to have originated.

There are five basic tuber types and a wide range of skin colors, from pure white, to red, purple, even brown. There are also discernible differences in flavor, but nearly all of the known varieties share in common a strong resemblance to the flavor of cooked artichokes, hence the name: artichoke of New Jerusalem. Most native peoples referred to the plant as a "sun root," which is botanically more correct. The Jerusalem artichoke has been hybridized with the sunflower to yield the Sunchoke, which is high in sugar and may eventually serve as a commercial source for sugar.

A number of Jerusalem artichoke cultivars are considered improvements over the knobby, hard to pare wild sorts. These include Challenger, French Mammoth, Skorospelka (developed in Russia), Stampede (developed by Ontario Indians), and Fuseau, a tapered sort resembling a sweet potato in shape which was developed in Egypt about 1913.

Maximilian's sunflower (Helianthus maximilianii). This is a near relative of the Jerusalem artichoke, which produces tubers or thick tuberous roots prepared and eaten in the same manner. It is native to the dry prairies of the Great Plains, where it was first identified by Prince Maximilian of Wied-Neuwied during a trip up the Missouri River between 1815 and 1817.

Water parsley (Oenanthe sarmentosa). An aquatic tuber with black skin and starchy white flesh tasting of parsley. It was highly esteemed by the native peoples of the Pacific Northwest.

Wild potato (Solanum fendleri and Solanum jamesii). These are small, marble-size potatoes found in the Southwest. They were gathered mostly by the Navajo, Hopi, and other native groups. The Fendler Wild Potato is said to taste like a chestnut when cooked. The Colorado Wild Potato (Solanum jamesii ) was eaten raw, baked or boiled and can be stored for long periods of time. It was also dried and ground to make flour. Both species contain bitter toxins that can be neutralized when cooked with an alkaline substance.

Wild sweet potato (Ipomoea pandurata). This is in most ways similar to the Bush Morning Glory, except that it has a vining habit and grows in the eastern regions of North America rather than on the Great Plains. It was considered an important food source by Eastern Woodlands peoples.

Wood sunflower (Helianthus strumosus). A near relative of the Jerusalem artichoke, the tubers are less well formed, more elongated and knobby. The flavor is similar to a Jerusalem artichoke. The plant grows in forest clearings in eastern North America and has become relatively rare. It is cultivated on a very limited basis by specialists interested in heirloom crops.

South America (Including Central America and Mexico)

This region of the world possesses the richest natural diversity of tuberous species, yet nowhere is the literature more confusing than from this continent. As the late Sophie Coe pointed out "the treachery of common names" can transform comparative research into linguistic nightmares, especially when it comes to cookery. Local names for plants change not only across national borders, but from one region to the next, and even among neighboring native languages. All of these aliases show up in regional cookbooks, which must be read with great care. The ocumo of Venezuela is the malanga of Puerto Rico and the quequisque of Nicaragua. Not all of the multitudes of local names are listed below, just those that are most commonly mentioned in culinary literature. Nor are all of the South American tubers included, since many of the minor ones like swamp lily (Thalia geniculata ) are consumed primarily or exclusively by indigenous ethnic groups. The tubers included here are those that play an important role in agriculture and kitchen gardens, and many of them are now commonly grown in other parts of the world.

Arrowroot (Maranta arundinacea). Some botanists refer to the root of this plant as a tuber when it is round and as a rhizome when it is long, even though the genetic material is identical. This difference in shape is owing to physical changes as the plant matures, but for the purposes of cookery, it is treated here as a tuber. This is a plant that grows on boggy ground or along steams, and in the West Indies where it originates, it was grated, boiled, or baked in the manner of a potato by the native peoples. Because it is so rich in starch, arrowroot became an article of trade by the eighteenth century, the starch being an ideal thickener in sauces as well as a basis for soupy gruels in invalid cookery. It also became one of the base thickeners for budín, and a key ingredient in delicate galletas. Arrowroot is now grown mainly as a source of culinary starch, but its culture has spread to several parts of the world. In Asia, it is planted along the borders of rice fields, so it is an important secondary crop for small-scale farming. It is also employed in the manufacture of noodles.

Cassava (Manihot esculenta). Also called manioc and yuca, cassava has become on of the most important food crops in the tropics, particularly in sub-Saharan Africa. The nutrient-rich leaves are boiled like spinach, the tuber cooked like potatoes, and the starch used for making tapioca. The genetic origin of the plant is tropical South America, most likely northeastern Brazil. It was brought under cultivation about 3,000 B.C.E., but had spread to many areas of Central America, Mexico, and the Caribbean by the time Columbus first saw it in 1492. It became an important military ration for the conquistadors because it could be stored for a long period of time. Since the 1500s, cassava has been introduced and thoroughly integrated into the agricultures of Asia and Africa. In South America entire cookbooks, such as Enrique Tercero Hoyos's Casabe (Bogotá, 1996), are devoted to the preparation of this vegetable. A more complete discussion of cassava and its complex history are provided in a separate article.

Cush-cush or Indian yam (Dioscorea trifida). Also called Mapuey. Compared with the more popular yams introduced from the Old World, this may be considered a minor crop limited to the northern coast of South America, parts of Central America, and the Caribbean. It has not received much attention in scientific literature, although it is the only New World yam raised for food. In Afro-Caribbean cookery, it is treated like the sweet potato and is superior in quality. The texture is very fine and creamy when mashed. There are several landraces, most with white flesh, others with rose or purple flesh.

Dahlia (Dahlia pinnata). The common garden dahlia now grown as an ornamental was not noticed by European horticulturists until it was sent to Spain in 1787. Prior to that, its tubers were cultivated or gathered from the wild by the native peoples of southwest Mexico. The dahlia is still considered one of the native ingredients in the cookery of Oaxaca, and the petals make a colorful addition to salads. Today, there are several cultivars raised especially for their large, sweet potato-like tubers. There the similarity stops, since these tubers do not cook soft, but rather retain a certain celery-like crispness that is ideal for vegetable stir-fries. The flavor is complex, something akin to steamed pumpkin with overtones of sunflower seeds and a hint of spinach. Dacopa, an intensely sweet extract from the tubers, is used to flavor beverages in Central America. This extract tastes like strong mocha.

Madeira vine (Andredera cordifolia). This fine ornamental vine, which was a popular verandah plant in Victorian America, is actually a very good garden vegetable with many overlooked qualities. Its succulent, fleshy leaves may be eaten raw or cooked, and its white, nutty tubers make excellent additions to a meal, especially because they retain their crispness if not cooked too long. Otherwise, when cooked soft, they resemble potatoes. This is a relative of Malabar spinach and ulluco, which is still commonly found in Central American markets. It originates in the tropical parts of South America, but outside the western hemisphere it is not widely dispersed as a food plant except for a few places in Asia, such as Japan and the Philippines.

Malanga (Xanthosoma sp. ). Christopher Columbus encountered this plant during his voyages to the New World but no one yet has established a universally accepted name. It was called taia in Carib, but goes by yautia or malanga in Spanish, ocumo in Venezulea, chou caraibe in the French West Indies, tannia and calaloo in the English-speaking islands, and quequisque in Nicaragua. The confusion is even greater since these names refer to specific species in some localities, while in others they are just general monikers to differentiate the plant from taro, which it resembles. The yautia amarilla of the Dominican Republic is Xanthosoma atrovirens and not any other yellow-tubered species, while the yautia morada of Puerto Rico is the same species as Nicaraguan quequisque (Xanthosoma violaceum ). To get it right in the marketplace, it is almost necessary to bring a botanist along. Confusion arises from the fact that within each species there are numerous varieties and indeed many named cultivars. To the subsistence farmers of the Caribbean and South American tropics where this plant originates, all of this does not matter; it is only how it tastes that counts.

The most commonly grown species is the white tubered sort called yautia blanca or malanga blanca (Xanthosoma saggittifolium ), a key ingredient in Cuban and Puerto Rican cookery. The differences between malanga and taro are very noticeable when subjected to comparative taste-testing. The malanga is finer textured, easier to digest, and contains more starch. The leaves, which are cooked like greens, are also richer in protein and minerals, and the Haitians believe they taste a bit like mild cabbage. The underground parts harvested are the lateral tubers, which means that by digging beside the plant, it is possible to remove tubers as needed without killing it. This low maintenance, perennial food supply is one reason that the vegetable is so popular among the rural poor in the tropics. It also grows in areas with less rainfall than required by taro and will even grow in well-drained uplands. For this reason, its cultivation has also spread to Hawaii, Malaysia, the Philippines, Indonesia, and much of Southeast Asia, where it is used like taro.

Mashua (Tropaeolum tuberosum). Also known as Añu, this species of the garden nasturtium has been cultivated since ancient times in the Andes and has no known ancestral forms. It grows like a typical vining nasturtium and produces red and yellow flowers during the summer, but requires day lengths of twelve to nine hours for tuberization. The tubers are cone-shaped and thickened toward the bottom. There are two distinct varieties, a white skinned tuber flushed with violet, and a red-speckled one with pale yellow skin. Both are cooked before they are eaten and taste much like Jerusalem artichokes. Like oca and ulluco, the plants are highly productive and easy to harvest. Historically, Inca generals shipped large quantities of the tuber along with their armies under the belief that it would suppress venery so that the soldiers would forget their wives and devote themselves more energetically to fighting. It does not seem to have this effect on the Spanish.

Oca (Oxalis tuberosa). Next to potatoes, oca wasand still remainsone of the most important tubers raised in the high Andes. It forms an historical triumvirate with the potato and ulluco, and speaks for the genius of the farmers who figured out how to coax prolific tuberization from plants that in the wild would never have supported the complex societies that later evolved in that part of the world. In fact, oca has been cultivated for so long that the ancestral plant is now lost.

Oca is rather hardy, with fleshy leaves and stems, and a multitude of colorful tubers that form very late in the season, when the days grow exceptionally short. In the Northern Hemisphere, this means that oca will not tuberize until late November; therefore, it must be grown in cold frames, polytunnels, or cool greenhouses in order to produce a crop. This is not a problem in the ocagrowing regions of the Andes, where frosts come late, but it has hindered the spread of oca to other parts of the world. The French and English, for example, experimented with oca in the 1820s, but it remained a curiosity, more ornamental than culinary.

Ocas are sold by color in Andean markets, and there seem to be at least 60 variant forms, from snowy whites to bright, waxy reds, even black. In spite of this biodiversity, which certainly excites the eyes of experimental chefs, ocas are essentially of two sorts: the sweet ones that are eaten raw or sun-dried like figs to make caui ; or the bitter ones that are boiled, and boiled again, then freeze-dried to make ckaya. Dried ocas are more nutritionally rich than freeze-dried potatoes (chuño ), and therefore form an important supplement to the Andean diet. Fresh ocas resemble miniature potatoes, even to the "eyes," which can be planted like potato eyes in the early spring. Europeans find them bland-tasting, but when added to soups or raw to salads, they greatly enhance the visual appeal of the dish. Furthermore, the Indians of the Andes consider oca a potent aphrodisiac, so there may be unsung benefits to promoting oca beyond its old native borders.

Potato (Solanum tuberosum). Known as papas in Quechua and in Spanish, potatoes have been cultivated in the Andes roughly since 3700 B.C.E. (there are scholars who argue for an even older date of domestication). Seven distinct species of potato are still cultivated in South America, although only Solanum tuberosum is presently grown worldwide. The long tubered species Solanum ajanhuiri was introduced to France from Peru about 1815. It is still cultivated by potato connoisseurs, especially the black variety called Negresse or Truffe de Chine, which has become popular with Parisian chefs because of its truffle-like flavor. A detailed discussion of the potato and its history and near relatives may be found in a separate article.

Sweet potato (Ipomoea batatas). This tuber was brought under cultivation along the western coast of South America about 2800 B.C.E. It spread to nearly all parts of South and Central America, but never reached Mexico proper. The early Spanish likened its flavor to marzipan, and it was this potato, not the Peruvian potato, that was first sent to Europe. Sweet potatoes were grouped into two basic types by indigenous peoples: a mealy, starchy type used for bread making, and the fine-grained sweet types known today. Since the Spanish preferred only the sweet types, the starchy types have become extinct, except for a small pocket of "relic" cultivars found in parts of the Pacific and among the Maori of New Zealand.

The history of the sweet potato is complex, for it is one of the few New World plants that spread beyond the hemisphere prior to European contact. For a fuller treatment of the sweet potato, refer to the article by that name.

Ulluco (Ullucus tuberosa). A relative of the tropical Malabar spinach, ulluco prefers growing conditions quite the opposite: short day length, high humidity, cool weather, ample rainfall. In the high Andes it has been interplanted with potatoes for thousands of years and is still grown in a region stretching from Bogotá, Colombia, into northern Argentina. It is one of the most frost-resistant of all the Andean tubers. Its native names are many, including lisas, papa lisas, chuguas, rubra, timbos, and melloca. The smooth-skinned tubers resemble miniature potatoes and are quite startling visually, coming in a rich array of yellows, purples or magentas, vibrant greens, and varieties that are speckled. There are six named cultivars which vary in sweetness or starch content. Some find the tubers bland when boiled, but when boiled and then fried, they taste like potatoes. They are also eaten raw with vinegar or dried in the sun to make lingli, an Andean snack food.

Yacon (Smallanthus sonchifolius). A near relative of the sunflower, yacon (pronounced ha-KON) has been cultivated in the Andes for almost 2,000 years and perhaps much longer. The name is a Spanish combination of Quechua yacu and unu, both of which mean water in the language of the Incas. This refers to the fact that the tubers are juicy like apples and will yield a pleasant beverage when pressed. This juice is also cooked down until thick to make a type of molasses called chancaca. The plant itself is a handsome ornamental, with large palmate leaves resembling tithonia. The leaves are used in medicinal teas and are considered antidiabetic. The long, smooth, sweet-tasting tubers were treated as fruit by all Andean peoples and are still sold among fruits in the country markets of Peru, Bolivia, and Ecuador.

Images of yacon tubers and leaves dating from 500 c.e. have been found on cloth fragments at Nazca in Peru, direct evidence that the plant was already considered an important food source. Genetic evidence of long cultivation is also evident, since many strains have been reproduced from cuttings for such a long time that the flowers have become infertile. It is known from early Spanish accounts that yacon was mostly planted along the margins of fields and that its cultivation was spread over a wide area of the Andes by the Incas in the period immediately preceding Spanish conquest. Because yacon is day-length sensitive, many species cannot be grown outside their native habitats. There is some effort at present to breed out this sensitivity so that yacon can be grown more easily in North America and Europe. Since yacon's sugars can be tolerated by diabetics and it is nutritionally very low in calories, the plant offers a number of interesting possibilities for further development.

Aside from the yacon discussed here, there are at least 20 other species of yacon found in Mexico, Central and South America. Only a few of these have been brought under cultivation, although several types were treated as "managed" plants by native peoples. That is, they were maintained in the wild rather than cultivated in fields. Many of the Central American yacons produce edible seeds that resemble small, black sunflower seeds. They make excellent bird feed and would probably appeal to humans if they could be bred to grow larger. The seed also yields an oil which is highly valued for its medical properties.

Yam bean (Pachyrrhizus erosus). Also known as ahipa, xiquima, and jicama, this is often described as a mono-tuberous root rather than a true tuber. Native peoples treated it as a tuber, and the Mayans included it in many of their food riddles, mentioning both yellow and white sorts. The plant is indeed a bean with a highly ornamental vine, but the beans themselves are toxic and narcotic. Only the tuber is eaten, and generally, if we are to judge by Aztec codices and early Spanish accounts, this meant eaten raw for its refreshing crispness.

The plant is native to tropical America, although its center of biodiversity appears to be Central America where other species are commonly found. The archeological record has not been helpful, but it is likely that the yam bean was domesticated in that part of the New World first, and then spread to other cultures. It was exported to the Philippines by the Spanish, and from there spread to other parts of Asia during the 1600s. It is now also grown in East Africa, where it has become quite common, although it is generally cooked.

It is also being marketed in the United States and Europe under the Mexican name jicama and plays an important role in Mexican and Central American cookery to this day.

See also Africa ; Aphrodisiacs ; Cassava ; Iberian Peninsula ; Japan ; Potato ; South America ; Sweet Potato .

BIBLIOGRAPHY

K. T. Achaya, Indian Food (Delhi: Oxford University Press, 1994); Emilii Bretschneider, History of European Botanical Discoveries in China (London: Samson Low, Marston, and Co., 1898); Sophie D. Coe, America's First Cuisines (Austin: University of Texas Press, 1994); L. Guarino, ed. Traditional African Vegetables (Rome: International Plant Genetic Resources Institute, 1997); U. P. Hedrick, ed. Sturtevant's Notes on Edible Plants (Albany: J. B. Lyon, 1919); G. A. Herklots, Vegetables in Southeast Asia (New York: Hafner Press, 1972); M. Hermann and J. Heller eds., Andean Roots and Tubers (Lima, Peru: Centro Internacional de la Papa, 1995); Udelgard Körber-Grohne, Nutzpflanzen in Deutschland (Stuttgart: K. Theiss, 1987); Janet Long, ed., Conquista y Comida: Consecuencias del Encuentro de dos Mundos (Mexico City: Universidad Nacional Autónoma de Mexico, 1996); Lucia Rojas de Perdomo, Cocina Prehispanica (Bogotá: Voluntad Interes General, 1994); Anna C. Roosevelt, Prehistoric Maize and Manioc Subsistence along the Amazon and Orinoco (New York: Academic Press, 1980); Alix Wilkinson, The Garden in Ancient Egypt (London: The Rubicon Press, 1996).

William Woys Weaver

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