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Economic Plant Photographs: Vegetables #1

Vegetables From Underground

Botanical vegetables include enlarged storage roots, corms, tubers and stems that are eaten by people. True botanical vegetables also include leaves, leaf stalks, flowers, buds, and just about any part of a plant except the fruit or seeds. Vegetables may also be defined loosely as a plant part that is eaten with your main entree, but generally not as a dessert.

Euphorbia Family (Euphorbiaceae): Cassava

Large storage root and palmately-divided leaf of the cassava plant (Manihot esculenta), a member of the diverse Euphorbia Family (Euphorbiaceae). Other common names for this important root crop include yuca, manioc and tapioca. In fact, the starchy root is the source of tapioca pudding. Cassava is the staff of life for millions of people living in tropical countries where cereals and potatoes will not grow. It is followed in importance by sweet potatoes (Ipomoea batatas) and true yams (Dioscorea).

Cassava plant (Manihot esculenta), showing the palmate leaves and large storage root. From a distance the foliage superficially resembles Indian hemp (Cannabis sativa).

Arum Family (Araceae): Taro

Corms of taro (Colocasia esculenta), a member of the Arum Family (Araceae). Corms are short, underground stems which lack the numerous eyes (buds) of potatoes. Like potatoes they are rich in starch grains (amyloplasts). Taro corms are rich in the soluble starch called amylose (soluble in hot water). The starch that is prevalent in most amyloplasts from other species is amylopectin (insoluble starch). Since they contain about 3% sugar, they are more like a sweet potato (Ipomoea batatas) than a true potato (Solanum tuberosum). Sweet potatoes are actually storage roots, while true potatoes are technically referred to as tubers. Taro has a long list of common names throughout tropical countries of the world, including cocoyam, kolocasi and ocumo. In the Caribbean region and elsewhere it is called dasheen. According to some botanists, dasheen is the variety antiquorum. The corms are baked like potatoes, roasted, steamed, or crushed to make cakes. Hawaiian poi is made by steaming the corm, followed by crushing and natural fermentation.

See The True Yam (Dioscorea)
See World's Largest Vegetable
  See Sweet Potatoes & Columbus  

Left: A cultivated field of taro (Colocasia esculenta) on the island of Moorea, a beautiful island in French Polynesia; Right: A taro pond in the Hanalei National Wildlife Refuge on the north side of Kauai (Hawaiian Islands). The pale green layer on the water surface is a dense population of the tropical duckweed Lemna aequinoctialis.

  See Dasheen In Caribbean Marketplace.  
Sweet Potato Yams Vs. Dioscorea Yams
See Sweet Potatoes And Jicama Root

Dioscorea Family (Dioscoreaceae): True Yams

Subterranean tuber of a true yam (Dioscorea sp.), the third most important tropical root crop after cassava and sweet potatoes. The venation and shiny, heart-shaped leaves of true yams are unmistakable compared to those of sweet potatoes and other root crops.

See The True Yam (Dioscorea)
  See Sweet Potatoes & Columbus

Nightshade Family (Solanaceae): Potatoes

Although the vast majority of people depend on wheat, corn and rice for food, the non-grain potato ranks fourth as a major food source. Columbus is often credited with bringing the white or Irish potato (Solanum tuberosum), a member of the nightshade family (Solanaceae), back to Spain, although most scholars argue that his reference to potatoes or "batatas" indicated sweet potatoes (Ipomoea batatas) rather than the Irish potato. Sweet potatoes belong to the morning-glory family (Convolvulaceae). Other Spanish explorers found true potatoes (called "papas") being grown by Indians all along the Andes from Colombia to Chile, and potatoes were known in Spain after 1565. Later, potatoes were introduced into the British Isles where they were grown extensively by the early 1800s. In fact, potatoes were so popular in Ireland that they became known as Irish potatoes even though their origin was South America. Ireland developed a monoculture of potatoes until the mid 1840s when their entire crop was devastated by the potato blight fungus (Phytophthora infestans). It has been estimated that during a five year period at least a million people died of starvation. The potato famine set into motion a wave of emigration that reduced Ireland's population by 50 percent between 1846 and 1900. The Irish constituted 35 percent of the immigrants to the United States during this period and became 15-18 percent of the population.

The common potato (Solanum tuberosum) is an autotetraploid species with a sporophyte chromosome number of 48 (4n=48). The normal sporophyte diploid number for the genus Solanum is 24. Eggplant (S. melongena) belongs to the genus Solanum and tomatoes (Lycopersicon esculentum) are closely related to the potato. Common potatoes (S. tuberosum) consist of two subspecies or groups, ssp. tuberosum ( "Chilotanum Group") and ssp. andigena ("Andigenum Group"). Older references state that potatoes taken to Europe in the sixteenth century all belonged to the andigena subspecies or "Andigenum Group" which was widely cultivated in the Andean highlands of Bolivia, Peru and northern Argentina. The origin of this tetraploid subspecies is controversial, but some authorities believe it resulted from hybridization between a diploid Andean species (S. stenotomum) and another diploid species (possibly S. sparsipilum), followed by autopolyploidy. The precise origin of the subspecies tuberosum or "Chilotanum Group" native to Chile is even more controversial, possibly derived from the subspecies andigena or the hybridization of subspecies andigena with yet another unknown Andean species. According to Mercedes Ames and David Spooner, the single Andigenum origin of the modern "European" potato (with cultivars grown worldwide) is not supported by plastid DNA studies from historical herbarium specimens. Their research points to a Chilotanum origin traced to a landrace indigenous to Chiloé, largest island in the Chiloé Archipelago off the coast of Chile. In addition, this research shows the critical importance of herbarium specimens in investigating historical origins of crop plants.

  Ghislain, M., J. Núñez, M. del Rosario Herrera, and D.M. Spooner. 2009. The Single Andigenum Origin of Neo-Tuberosum Materials is Not Supported by Microsatellite and Plastid Marker Analyses. Theoretical Applied Genetics 118: 963-969.

  Juzepczuk, S.W., and S.M. Bukasov. 1929. "A Contribution to the Question of the Origin of the Potato." TrVses Azeda Genet Selek 3: 593-611 (in Russian, English summary).

  Ames, Mercedes and David D. Spooner. 2008. "DNA From Herbarium Specimens Settles a Controversy About Origins of the European Potato." American Journal of Botany 95 (2): 252-257.

In contrast to true cultivated varieties (cultivars), landraces are grown from seed that has not been selected or developed by plant breeders. Landrace refers to domesticated plants or animals adapted to local natural and cultural environments. They typically develop naturally with minimal assistance from people, and without modern breeding techniques. Landraces differ from modern breeds and cultivars, and usually possess more diverse phenotypes and genotypes. A classic plant example is the 'Almagro' eggplant, a popular European variety that is used for pickling. It has an enlarged, prickly calyx that covers the fruit. This unusual eggplant is technically a "landrace" locally grown in central Spain. Animal examples include Shetland Sheep that originated in the Shetland Isles and Welsh Mountain Sheep indigenous to Wales. It should be noted here that many original landraces have been developed into modern breeds. For example, the Border Collie landrace native to Scotland and northern England, with more variable phenotypes, has been developed into a Border Collie breed with more consistent phenotypes.
  See The 'Almagro' Eggplant  

Whatever the exact origin of our common potatoes, they have become a major food source in the Old and New World temperate regions. Potatoes are an excellent low sodium source of complex carbohydrates. One average-sized baked potato is only about 100 dieter's calories (kilocalories), unless of course it is piled with butter and sour cream. Potatoes are used for all sorts of delicious foods, including French fries, mashed potatoes, potato pancakes, hash browns and potato chips. In Poland, a vodka that is almost 200 proof (nearly 100 percent ethanol) is made from potatoes. It should be noted here that potatoes have a high glycemic index and probably should be eaten in moderation or avoided by diabetics and people trying to lose weight.

  Insulin Resistance & High Glycemic Foods   

The thin-walled parenchyma cells of a potato tuber are filled with membrane-bound, starch-storage organelles called amyloplasts. They are also referred to as "starch grains" in most general biology textbooks. Since iodine stain (gram's iodine) makes starch turn purplish-black, the amyloplasts can easily be viewed with a compound microscope (400X). Insoluble starch (amylopectin) is deposited in concentric layers within the amlyloplasts. Unlike the long, coiled molecules of soluble starch (amylose), the molecules of amylopectin are much shorter, with only 40-60 glucose subunits. Amylopectin molecules consist of highly branched chains that do not coil. Starch grains of different plant species have characteristic shapes, such as maize (corn), oats, bananas, potatoes and wheat. For example, banana starch grains are more elongate than potato starch grains. Starch is hydrolyzed (broken down) by amylase enzymes (including B-amylase and maltase). During hydrolysis a water molecule is inserted between each glucose subunit. Starch is typically stored in underground organs, including storage roots, rhizomes, tubers, corms and bulbs.

Magnified view (400X) of several parenchyma cells of a potato tuber showing the thin, transparent cell walls and clusters of amyloplasts (starch grains). The starch grains were stained black with gram's iodine.

See Tomatoes, Tomatillo & Eggplant
  Go To Starch On Plant Chemistry Page  

Because sweet potatoes (Ipomoea batatas) thrive in a hot, moist climate, while potatoes (Solanum tuberosum) require a cool climate, they have never become as popular as the Irish potato in Europe. Sweet potatoes have become an important root crop in warm subtropical and tropical countries, second only to cassava or manioc (Manihot esculenta), a member of the euphorbia family (Euphorbiaceae) and the source of tapioca. Archaeological evidence shows that sweet potatoes were cultivated in South America by 2400 B.C. and fossilized sweet potatoes from the Andes have been dated at 8,000 to 10,000 years old. Although the sweet potato is clearly native to South America, it was also cultivated in Polynesia as early as 1200 A.D. In fact, the sweet potato had already become the principle food of the Maoris in New Zealand by the time of Captain Cook's historic voyage to that part of the world in 1769. It is interesting to note that the sweet potato is known as "kumar" or "kumal" in the Lima region of Coastal Peru, and it is called "kumara" by the Maoris of New Zealand. In his book, Sea Routes to Polynesia (1968), Thor Heyerdahl postulated that sweet potatoes were carried across the Pacific by Peruvian Indians before Europeans began to sail the world's oceans. He tested his hypothesis in 1947 by sailing a balsa wood raft, the kon-tiki, fashioned after the reed rafts of the Oru Indians living on Lake Titicaca in Bolivia. Although Heyerdahl's hypothesis about the transoceanic exchange of sweet potatoes by skillful pre-columbian sailors remains an enigma (at least to some skeptics), his New World origin for the coconut (Cocos nucifera) has been rejected by most botanists. Widespread sea dispersal of wild-type coconuts, the remarkable dispersal of coconut crab larvae riding on coconuts, and fossil evidence of Miocene coconuts in the South Pacific indicate an Indo-Pacific origin, long before the voyages of ancient mariners. Most authorities now agree that the coconut was introduced to the New World by Portuguese and Spanish traders.

Unlike the stem tubers of Irish potatoes, sweet potatoes are fascicled (clustered) storage roots. Irish potatoes are propagated by planting sections of the tuber containing an "eye" or bud. Potatoes used for propagation are called "seed potatoes." Sweet potatoes do not have "eyes" and cannot be propagated by planting pieces of the root in the ground, although they will sprout in a glass of water. There are a number of cultivated varieties of Irish potatoes, including 'Russet,' 'White,' and 'Red Rose.'

Three varieties of potatoes (Solanum tuberosum). 'Russet' (left), 'White' (right), and 'Red Rose' (center).

Potato (Solanum tuberosum), showing rhizome, young tuber and older tuber.

  Sweet Potato Yams & Dioscorea Yams  
See The True Yam Named Dioscorea
See Sweet Potatoes And Jicama Root
See Tomatoes, Tomatillo & Eggplant

Large field of "papas" or potatoes (Solanum tuberosum) in the cool foothills of Cerro de la Muerte in Costa Rica.

A field of potatoes (Solanum tuberosum) in the Anza-Borrego Desert of San Diego County. The potato belongs to the same genus as eggplant. There are many varieties of potatoes grown throughout the United States.

Poisonous old potatoes: The green, leafy sprouts and green skin contain solanine, a toxic alkaloidal glycoside (sugar + steroidal alkaloid) that can cause gastroenteritis. In fact, this toxic glycoside is not destroyed when green potatoes are cooked. The potatoes must be carefully peeled first.

These ripe potato fruits are similar to the tomato (Lycopersicon esculentum). Unlike the tubers, potato fruits contains the toxic alkaloid solanine and are not recommended for human consumption.

Sunflower Family (Asteraceae): Jerusalem Artichoke

The Jerusalem artichoke (Helianthus tuberosus) is a large, perennial sunflower native to the Great Plains of North America. It is closely related to the common sunflower (H. annuus) that grows along roadsides and vacant fields throughout the western United States. It has been cultivated by native Americans for centuries, and was introduced into Europe in the early 1600s. Like true potatoes, it produces edible tubers at the ends of underground stems called rhizomes. The tubers contain "eyes" or buds and are technically modified stems rather than roots. [The original name of "sunchoke" was applied to a hybrid between the Jerusalem artichoke and the common sunflower.] The common name may have been corrupted from the Italian name for the plant "girasole articiocco." "Girasole" refers to the way the flowers turn to face the sun, and "articiocco" refers to artichoke. Some people say the tubers taste like artichoke hearts if they are steamed with the peel on. The peel imparts the artichoke flavor to this vegetable. The tubers are eaten raw in salads, steamed, fried, baked and mashed. Raw tubers are very crisp and sweet, with a taste more like water chestnuts than potatoes. Jerusalem artichokes provide an abundant source of nutritious, tasty tubers in poor soils with very little care.

Left: Common sunflower (Helianthus annuus), a widespread North American wildflower along roadsides and vacant fields. Right: Edible, starchy tubers of Jerusalem artichoke or sunchoke (H. tuberosus), another North American wildflower native to the Great Plains.

The tubers of Jerusalem artichoke contain fewer calories than potatoes, and they are especially high in vitamin A, the B-complex, potassium and phosphorus. They contain the polysaccharide inulin instead of starch, which is a nutritious food for diabetics and hypoglycemics. The hydrolysis of inulin yields fruit sugar (D-fructose), while true insoluble starch (amylopectin) yields D-glucose. [Starch (amylum) is actually composed of two polymers, soluble starch (amylose) and insoluble amylopectin. Starch polymers are packed into membrane-bound starch grains or amyloplasts within plant cells.] Sugars from the digestion of inulin do not elicit rapid insulin production compared with other starchy foods.

  Read About Soluble & Insoluble Starches  

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