Tomato, Tomatillo, Eggplant, Nipplefruit & Chayote

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Economic Plant Photographs #21

Tomato, Tomatillo, Eggplant, Nipplefruit & Chayote
© W.P. Armstrong 3 April 2008 (updated 24 July 2011)
Nightshade Family (Solanaceae)

The nightshade family (Solanaceae) includes several species of fruits which are better-known as vegetables to most people. Since they are typically eaten with a main entree or in a salad (and not as a dessert), they are usually called vegetables. Botanically speaking, these "vegetables" are technically botanical fruits because they are seed-bearing structures that develop from the ripened ovaries of flowers. The cultivated tomato (Lycopersicon esculentum) is native to South America, although archaeological evidence suggests that it was domesticated in Mexico and Central America. The Maya called the fruit tomatl, a name that was corrupted by the Spanish into tomate, and by the English into tomato. Because of its flower structure, the tomato is obviously closely related to the genus Solanum which includes the potato (S. tuberosum), eggplant (S. melongena), and a number of species called nightshades. The generic name Lycopersicon "wolf-peach" is derived from the Greek words lyco "wolf" and persicum "peach." It was placed in this genus by Philip Miller in 1768, although Linnaeus had placed it in the genus Solanum in 1753. The scientific and common names for the nightshade family (Solanaceae) are derived from the type genus Solanum. Recent studies using chloroplast DNA corroborate the genetic affinity between nightshades (Solanum) and tomatoes (Lycopersicon). Some species of nightshades contain several toxic alkaloids. In fact, the tomato was once considered to be inedible and poisonous in the United States until the early 1800s. The Old World ornamental Jerusalem cherry (S. pseudocapsicum) produces small tomatolike fruits that contain the poisonous alkaloid solanocapsine. Tomatoes are grown extensively in California's Central Valley for tomato juice, canned tomatoes, tomato paste, catsup, and for the various salsas used in popular Mexican dishes.

Andrew F. Smith discusses the reluctance to eat tomatoes in his book The Tomato in America: Early History, Culture, and Cookery, University of South Carolina Press, 1994: "While some Americans obviously did believe that tomatoes were poisonous, this phenomenon has been blown out of proportion by well-intentioned popular historians." In Chapter 3 he gives some of the reasons why Americans did not eat tomatoes in the 1800s, including taste, smell, appearance, and a general fear of vegetables. Other myths and unfounded beliefs about tomatoes are discussed by David Gentilcore in Pomodoro: A History of the Tomato in Italy (Arts and Traditions of the Table: Perspectives on Culinary History), Columbia University Press, 2010.

Fruit or Vegetable?

The controversy over whether a tomato is a fruit or vegetable reached the U.S. Supreme Court. A tariff law that imposed a duty on vegetables but not fruits caused the tomato's status to become a matter of legal importance. On February 4, 1887 action was brought against the collector of the port of New York to recover back duties paid under protest on tomatoes imported by the plaintiff from the West Indies, which the collector assessed under the Tariff Act of March 3, 1883. This controversy was settled in 1893 when the U.S. Supreme Court declared that the tomato was a vegetable. The Court's official interpretation was based on the popular dictionary definition which classifies a vegetable as something eaten at dinner with your main entree, but not as a dessert. The case is known as Nix v. Hedden, 149 U.S. 304 (May 10, 1893).

The tomato (Lycopersicon esculentum) is a botanical fruit. Because
the entire fruit wall or pericarp is fleshy, it is technically called a berry.

The nightshade family (Solanaceae) contains many species with poisonous alkaloids, including tobacco (Nicotiana tabacum), deadly nightshade (Atropa belladonna), mandrake (Mandragora officinarum) and the deadly datura species (Datura and Brugmansia). Some of the toxic alkaloids include nicotine, atropine, hyoscyamine, scopolamine and solanine. In addition, the chile peppers (Capsicum) contain the alkaloid capsaicin which is used to enhance the flavor of foods and in self defense sprays. Although the jimsonweed (Datura wrightii) contains several toxic alkaloids, its foliage provides the natural food supply for several species of large caterpillars called tomato hornworms (Manduca sexta and M. quinquemaculata). These same larvae also are fond of tomatoes, and can literally devour the leaves of tomato plants. The larvae undergo metamorphosis under the ground and change into magnificent night-flying hawkmoths the size of hummingbirds.

Go To Article About Chile Peppers
Go To Article About Plant Alkaloids
See Moth That Is Fond Of Tomatoes

Vine-ripened tomatoes have a much better flavor and texture, compared with typical supermarket tomatoes that are picked green. Tomatoes that ripen on the vine are superior because of a natural hormone called ethylene that is produced by the plant. Ethylene is responsible for the rapid maturation of tomatoes, including the color change, softening, increased sugar content and flavor production. Because the ethylene ripening process occurs very rapidly, the shipping, storage and shelf life of vine-ripened tomatoes is greatly reduced. Consequently, the tomatoes are picked green during the handling process, and then later exposed to ethylene gas to hasten ripening; however, they still don't have the natural flavor and texture of vine-ripened tomatoes. The production of ethylene and the softening of the fruit wall requires the production of specific enzymes. For example, pectinase enzymes break down pectin in the middle lamella layer between cells causing the fruit wall tissue to decompose rapidly. By introducing synthetic genes into the tomato nuclear genome, enzyme production can be blocked. The synthetic genes produce complimentary RNA strands that bind to the normal RNA that codes for the fruit ripening genes. In other words, the normal RNA is blocked so that translation and enzyme synthesis at the ribosomes does not occur. Genetically engineered tomato plants have been produced with delayed fruit ripening and softening. The fruits can be picked at the final stages of ripening, but will not get soft and mushy. A later treatment with ethylene causes the final softening and ripening to resume, just in time for the grocer's shelves.

Most popular supermarket tomatoes are parthenocarpic, a term that applies to seedless fruits that develop without fertilization. Parthenocarpy can be induced artificially by the application of dilute hormone sprays (such as auxins) to the flowers. Auxins are growth hormones produced primarily in the apical meristems, buds, and young leaves of plants. The primary plant auxin is indoleacetic acid (IAA), which is synthesized from an amino acid. Auxins and other plant hormones are involved in numerous developmental aspects of plant growth, including floral initiation, sex determination, growth rate, fruit growth and ripening, abscission, rooting, aging, dormancy, and apical dominance.

Ripe tomatoes are particularly rich in the carotenoid lycopene (C40H56). In addition to imparting the bright red color to tomatoes, 40 milligrams of lycopene ingested daily may reduce the risk of atherosclerosis (clogged arteries) and heart disease. Lycopene may also reduce the risk of certain cancers, including cancers of the prostate, lung, bladder, cervix, skin and digestive tract. According to Dr. A.V. Rao (Experimental Biology and Medicine 227 (10): 908-913, 2002), lycopene is an antioxidant that prevents the oxidation of low density lipoproteins (LDLs). High LDL oxidation is associated with increased risk of atherosclerosis and coronary heart disease. According to the Merck Index (1983), one kilogram (2.2 pounds) of fresh tomatoes yields 20 milligrams of lycopene. To obtain 40 milligrams of lycopene, you would need to eat about eight medium-sized tomatoes (or four large tomatoes) every day. Apparently lycopene is absorbed more readily in the processed form, such as tomato paste and juices. Several on-line references recommended drinking two glasses of tomato juice every day. Perhaps it is also wise to eat plenty of tomato soup, stewed tomatoes and tomato sauce on pasta and pizzas.

According to Dr. Leticia Rao, Assistant Professor of Medicine at University of Toronto, 10 milligrams of lycopene daily may prevent bone deterioration known as osteoporosis (Bottom Line Health Vol. 17, September 2003). This amount of lycopene equates to a 12 ounce glass of tomato juice, one 12 ounce can of tomato sauce, or one large tomato.

An interesting tomato relative is called ground cherry or tomatillo (Physalis ixocarpa). As the fruit develops into a fleshy, tomatolike berry, the outer calyx of the flower also enlarges into an inflated, papery, bladderlike sheath that encloses the berry. The unripe fruits are used in salsa verde, a mildly hot chili sauce often served with tacos, enchiladas, tostadas and other Mexican dishes. They are also stewed, fried, baked, and used in dressings and soups. Ripe fruits can be eaten raw, in sandwiches and salads. There are several wild species of Physalis called ground cherries in the mountain and desert regions of southern California, including P. greenei and P. crassifolia. A Peruvian species (P. peruviana) is naturalized in the Hawaiian Islands. It is called "poha" and the berries are eaten fresh and used in jams and jellies.

Green berries of tomatillo (Physalis ixocarpa) enclosed by papery, inflated calyx.

These tomato-like green fruits are actually from the closely-related potato (Solanum tuberosum).

Another interesting tomato relative is the eggplant (Solanum melongena) native to tropical Asia (India or southern China). Like zucchini gourds, eggplants are typically picked when immature so they usually don't contain mature seeds in the fruit pulp. Some of the cultivars include the large oval fruits of 'Black Beauty' or the elongate, slender fruits of 'Japanese.' Some of the smaller ornamental varieties actually resemble chicken eggs in size and color. Although the potato (S. tuberosum) belongs to the same genus as eggplant, it rarely produces fruits. The leaves, stems, fruits, and the sprouts and green skin of old potato tubers contain the poisonous, bitter alkaloids solanine and solanidine. Sliced eggplant fruits are commonly fried, baked, stewed and grilled. They are the key ingredient for many delicious entrees.

An eggplant (Solanum melongena) showing the typical nightshade flower and large, oval fruit. Nightshade flowers typically have the five connivent anthers closely bunched together, but not truly fused as in connate anthers. This is the popular cultivar 'Black Beauty.'

A Japanese eggplant cultivar (Solanum melongena cv. 'Japanese') showing the typical nightshade flower and shiny, black fruit. This cultivar has a more elongate, slender fruit than the "Black Beauty' cultivar.

Two cultivars of eggplant (Solanum melongena). The popular cultivar 'Black Beauty' (left) has a larger, oval fruit. Another popular cultivar 'Japanese' (right) has a more elongate, slender fruit.

The Almagro Eggplant: A Landrace Originating In Central Spain

The 'Almagro' eggplant is a popular European variety that is used for pickling. Note the enlarged, prickly calyx that covers the fruit. This unusual eggplant is technically a "landrace" locally grown in central Spain. 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 animals or plants 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. 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.

A field of potatoes (Solanum tuberosum) in the Anza-Borrego Desert of San Diego County. The potato belongs to the same genus as eggplant. Unlike the eggplant, potato plants are grown for their starchy, underground tubers.

See Article About Botanical Vegetables
See Article About Irish Potatoes

Another semi-woody species of Solanum from lowland tropical America is called nipplefruit (S. mammosum). This prickly shrub is grown as an ornamental because of its bright orange fruit with basal nipplelike projections. The fruits are considered toxic and are usually not eaten.

Nipplefruits (Solanum mammosum) in Thailand.

Gourd Family (Cucurbitaceae)

Chayote (Sechium edule), an interesting one-seeded fruit in the gourd family (Cucurbitaceae) that is typically cooked and eaten as a vegetable. It comes from a tendril-bearing, perennial vine native to tropical America. Unlike most members of the gourd family with many seeds embedded in the fleshy endocarp tissue, the fruit of chayote contains a single seed. The large seed has the unusual property of germinating while still inside the pear-shaped fruit. In fact, for propagation the entire fruit is often planted, rather than extracting the seed. Culinary uses of chayote fruits are similar to zucchini squash, including stewed, fried and boiled. The young shoots are sometimes cooked like asparagus, and even the starchy, tuberous roots are cooked and eaten.

See More Fruits In The Gourd Family

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