NUTS. Botanically, a nut is a hard, one-seeded fruit that is indehiscent, which means it does not split open on its own at maturity. Many commercial nuts, however, do not meet the strict botanical definition. One common characteristic of nuts is a hard outer covering or shell. The shell is a natural package that protects the inner seed, usually very high in food value, from animal predation. To overcome thick nutshells, humans (and other primates) developed tools. The most primitive tools are rocks used by chimpanzees for cracking nuts. Some scientists speculate that the shards broken from such primitive nutcrackers may have been the first scraping and cutting tools used by early humans as they gradually developed and improved technology.
Nuts may have helped spark early humans' technological creativity by coupling a challenge with a nutritious reward. The hard nutshell is a challenge that must be overcome to gain the reward of the kernel and has become a metaphor for a challenging puzzle, "a hard nut to crack." The names given to nuts by indigenous people sometimes reflect the effort of cracking. The word pacan, for example, was used by Native Americans to refer to all hard-shelled nuts that required an instrument (stone or hammer) to crack. The folds, wrinkles, and lobes of walnut kernels bear a resemblance to the brain, and are similarly encased in a skull-like protective case. Under the "Doctrine of Signatures," a medical system used in the sixteenth and seventeenth centuries, that similarity was considered meaningful so walnuts were prescribed for maladies related to the head. It may be from such visual, verbal, and historical connections that the term "nut" came to be associated with the head, as well as with an idiosyncratic personality.
Modern technology has provided global access to a wide range of nut crops, at the same time threatening the maintenance of the genetic and ethnobotanical diversity that produced them. Perhaps exploring the variety of nut crops within the context of their usefulness to humanity will contribute to improved stewardship.
Almonds (Prunus dulcis [Miller] D. A. Webb)
Plant biology. The almond is a deciduous tree of the arid temperate zone. It grows to a height of twenty-five to thirty feet and has white to pink solitary flowers, 1–1.5 inches across, that develop with or before the early foliage. The flowers of most almond cultivars are self-incompatible, although there is selection for self-compatibility, especially in Europe. Honeybees typically transfer the heavy pollen. The flower has a single pistil with two ovules. If both develop, an undesirable "double kernel" is produced. The fruit is a compressed, pubescent, oblong-ovoid drupe that splits at maturity to reveal the shallow pitted stone containing the seed (the edible kernel).
Almonds are a concentrated source of energy, being relatively high in fat (54 percent, see Table 1). The fatty acid in highest concentration is oleic acid (70–78 percent), a monounsaturated fatty acid that can contribute to lowered cholesterol levels. Kernels are also relatively
|Nutritive value and composition of major nut crops|
|Crop||% water||% protein||% fat||% sat||% oleic||% linoleic||% carb||minerals||cal/g|
high in protein (18 percent). Seedlings vary in kernel quality, with some producing bitter kernels due to high levels of the glucoside amygdalin. Amygdalin is hydrolyzed by the enzyme emulsin to form benzaldehyde and cyanide, which cause the bitter taste. Substrate and enzyme are both present in the seed and are united when cells are injured, as occurs during consumption. The trait has adaptive value as a protection against predation.
History. Almonds originated in Asia and moved with the migrations of peoples, which were often impelled by the upheavals of famine and warfare. In Genesis 43:11, the patriarch Jacob instructed his sons to carry almonds and pistachio nuts from their home in Palestine to Egypt when the family had to relocate during a period of extreme famine (c. nineteenth century b.c.e.).
The almond may have been introduced in Greece during the conquests of Alexander the Great (c.320 b.c.e.). From Greece, almonds spread into Italy and the Mediterranean region, a movement that can be traced in the etymology of the English word. "Almond" is derived from the French amande, from the Latin amygdala, which came from the Greek.
The Arab conquest of North Africa in the sixth and seventh centuries started another wave of almond introductions. The Moors took almonds with them when they conquered southern Spain. Almonds were then transported from Spain to California during the Spanish Mission Period (1800). The warm, dry climate of California, coupled with intensive agricultural systems, led to the preeminence of California in world almond production.
Almonds are currently grown in regions characterized by a subtropical Mediterranean climate. Primary production centers are the central valleys of California, the Mediterranean region, and Central to Southwestern Asia.
Procurement. In California, culture is intensive. Cultivars are selected for high production of soft-shelled kernels. Grafted trees of improved cultivars are propagated on rootstocks selected for the constraints of particular sites. Trees are planted in irrigated orchard configurations with densities of up to 134 per acre. Two rows of the main cultivar to one row of a pollinizer are planted and hives of bees are maintained to aid pollination. Trees are heavily fertilized and protected with chemical pesticides, and yields of over 3,000 pounds of kernels per acre are achieved. Harvest operations are heavily mechanized, with specialized machines to shake nuts from the tree and others to collect them from the orchard floor.
In the Mediterranean region of production, culture is not as intensive, and many orchards are composed of selected seedlings rather than grafted trees. Furthermore, most classes and cultivars are hard-or semi-hard-shelled. Orchards contain fewer trees than in California, with only fifty to seventy trees per acre being typical. Selection has occurred within particular regions that have become identifiable for the class of almonds produced, despite heterogeneity. For instance, the Spanish island Majorca is known for the Farmer Majorca class, composed of a multitude of related seedling trees. Recent selection has been for late-blooming cultivars that avoid frost damage, for self-compatibility, and for adaptation to the environmental stresses that are not as completely controlled as in California.
Global and contemporary issues. Standardization accompanying globalization puts pressure on diversity. Increased uniformity allows increased mechanization, and may contribute to marketability and even profitability, but at the cost of genetic diversity. Small areas in the Mediterranean once comprised distinct land races of selected seedlings. The diversity of those local populations is being reduced as grafted culture increases. Maintenance of ex situ germ plasm collections cannot substitute for the continued selection of desirable seedlings by multiple local growers.
Brazil Nuts (Bertholletia excelsa Humbl. & Bonpl.)
Plant biology. Brazil nuts are produced by giant evergreen trees indigenous to the Amazon forest of South America. Trees may reach heights of over 160 feet, and form part of the upper forest canopy. Cream-colored flowers are borne in racemes at the ends of shoots, and have both male and female parts. Female Euglossine bees accomplish pollination, while males of that species primarily visit orchids. Flowers mature and drop quickly, within a single day. Fruit matures in fourteen months, falling from the tree from January to June. The fruit is a four-to six-inch spherical pod with a thick outer shell encasing twelve to twenty-four wedge-shaped nuts, each in its own dark brown rough shell. Each nut is two inches long or more and has a single solid kernel. Kernels are about 66 percent fat, 20 percent of which is saturated (see Table 1). The high oil content makes the nuts valuable as a source of oil for cosmetics and soap making, as well as for consumption. The nuts are about 14 percent protein and are a concentrated source of selenium, which is being studied for its role in preventing some forms of cancer.
History. Although Brazil nuts have been used by indigenous people of the Amazon for millennia, they were "discovered" by the outside world in 1569 when Juan Alvarez Maldonado was directed to the nuts by the Cayanpuxes Indians on the Madre de Dios River. The Spanish called the nuts "almendras de los Andes" or "almonds of the Andes." Dutch merchants began trading for Brazil nuts in the early 1600s, but it was not until the beginning of the nineteenth century that the tree was given its botanical name. The German botanist Alexander von Humboldt and his French colleague Aime Bonpland went on an expedition to Brazil in 1799; following their return to Paris about five years later, the men named the nut after von Humboldt's friend Claude Louis Berthollet. Brazil nuts became a traditional Christmas delicacy in England in the nineteenth century, and the market for the nuts soared as rubber exports increased in the last half of the century: the settlers who ventured into the forest to harvest rubber also harvested the Brazil nuts. When the market for rubber dropped, the demand for Brazil nuts remained consistent and has continued to support the castaneros who make their living harvesting the wild trees. The value of the nuts is dependable enough to serve as a type of currency in the area where they are grown.
Procurement. Brazil nuts are the only globally distributed nut crop produced almost entirely from wild trees. The long time required to establish a bearing tree, and low yields related to problems with pollination in established orchards, have made plantations of the trees economically unattractive. Most nuts come from the Brazilian states of Para, Amazonas, and Acre. Brazil nuts are also produced in Bolivia, Peru, Colombia, the Guianas, and Venezuela. A single tree may produce over 300 of the heavy, nut-filled pods. Castaneros do not stand under the trees in windy conditions to avoid being hit and possibly killed by the falling pods. Most collecting is done in the morning, and an experienced worker can collect close to a thousand pods in a day. Pods are opened with a machete, and nuts are carried to the river in sacks often weighing over one hundred pounds. They are taken by canoe or raft to marketing centers, where a few exporters accumulate and market the crop and receive the majority of the profit.
Global and contemporary issues. Increased attention has focused on Brazil nuts as a "keystone species," a species critical to the intricately interwoven web of life for many organisms. Studies in the wild have revealed the role of specialized bees for pollination, a factor that may be missing in planted orchards. The agouti, a large rodent, is unique in its ability to open the pods and to scatter-hoard the nuts, contributing to seedling establishment. Other organisms rely on the empty pods as a substrate for development. In recognition of their value to local people, laws in several countries prevent cutting down Brazil nut trees. Creative efforts are being made by local people to market the valuable crop directly and establish a sustainable ecological and economic system centered on this valuable nut tree.
Cashew Nuts (Anacardium occidentale L.)
Plant biology. The cashew tree is a medium-sized (up to forty feet tall), spreading evergreen tree that originated on the dry, salty coastal beaches of northeast Brazil. Trees have a deep taproot and extensive lateral roots that adapt them to their habitat. Leaves are simple and alternate, with entire margins. Flowers may be unisexual or perfect and are borne in terminal-branching panicles. The fruit is composed of a greatly enlarged receptacle, sometimes called the "cashew apple," at the base of which develops a thick-shelled, single-seeded, kidney-shaped nut. Inside the nut is the edible kernel, covered with another, thinner shell. Between the outer and inner shells is a thick, caustic oil called "cardol" that can cause blisters and must be removed. The kernels are roasted to remove toxins. Cashews are lower in oil than many nuts, having only 45 percent. The primary oil is oleic acid. Kernels are relatively high in carbohydrates (see Table 1). In addition to the edible nuts, the peduncle (or apple) can be eaten, pressed for juice, or used to make wine. The caustic nutshell liquid (CNSL) has heat-absorbing properties that make it useful in several industrial applications, from clutch facings to waterproof paints. Other plant parts are also useful: sap is used as insect repellent and varnish, and leaves and bark are used medicinally.
History. Indigenous people of Brazil were using cashew nuts and apples when the first Europeans visited in the mid-1500s. The Portuguese introduced trees to India in the 1560s, from which the species spread to other tropical parts of Asia. India was the source of the first international trade in cashews in 1907, exporting 430 tons of kernels to Britain and importing unshelled nuts from East Africa.
Procurement. The World Bank estimates that 97 percent of world cashew production is from "wild trees" (self-sown rather than systematically planted in orchards), although research on crop improvement is proceeding in Brazil, India, and Africa. Seedlings are capable of producing nuts only three years after planting. The vast majority of the very perishable cashew apples are allowed to rot rather than being processed. Yield from a mature cashew tree is estimated at between 100 and 150 pounds of fruit (apples and nuts), from which twenty pounds of hulled, unshelled nuts can be obtained, yielding about six pounds of kernels. Nuts are dried immediately after harvest, and then must be roasted to remove the caustic nutshell liquid, which complicates processing. Traditional methods of roasting result in the loss of the CNSL, as well as causing hazardous working conditions due to spurting oils and toxic smoke. More modern extraction methods salvage the CNSL, but require expensive solvents and technical expertise.
Chestnuts (Castanea spp.)
Plant biology. Chestnuts are deciduous trees with simple, alternate leaves that have serrate to dentate margins. Chestnuts are monoecious, with separate male and female flowers on the same tree. Male flowers are borne as unisexual catkins at the terminal end of shoots and as bisexual catkins on the lower shoots. Female flowers appear singly or in clusters of two or three at the base of the bisexual catkins and become the nut-bearing burrs. Male flowers tend to shed pollen prior to female receptivity, creating a tendency to cross-pollination. Pollen is primarily wind disseminated. The fruit is a spiny burr that dehisces into four valves at maturity to reveal three nuts. Chestnuts are rich reddish brown with a conspicuous pale oval scar at the base. The shell is relatively thin and is not as protective as the burr is. When the shell is removed, a hairy pellicle (seed coat) covers the embryo and two irregular cotyledons. Chestnuts have the highest water content, the lowest fat content, and the highest carbohydrate (starch) content of any nut crop (see Table 1). If chestnuts dry after harvesting, some of the starch converts to sugar and viability of the seed is lost. As a result, post-harvest handling dramatically affects both the edible quality of the product as well as its viability for seed.
Three species account for the majority of world production: the Chinese chestnut (Castanea mollissima [Bl.]), the European chestnut (C. sativa [Mill.]), and the Japanese chestnut (C. crenata [Sieb & Zucc.]). All species have a somatic chromosome number of 2n 24 and hybridize freely.
History. Seven species of Castanea are found around the world in the temperate zone, and each has a long history of utilization. The Japanese chestnut is native to the Japanese islands and Korea and has been cultivated for over 2,000 years, with some cultivars being maintained since 750 c.e. The species is considered the most domesticated, with the largest fruit, the most precocious seedlings, and the smallest mature tree size. Unfortunately, some of them produce nuts that are not very palatable until they have been cooked.
Most chestnuts consumed in Europe and the United States are derived from the European chestnut, which has been cultivated in southern Europe and Asia Minor since the Roman Empire. Increasingly, hybrids between the European and Japanese chestnuts are grown commercially because the latter species is resistant to ink disease.
American chestnuts (C. dentata [Marsh.] Borkh) were a dominant tree in the eastern forests of North America until ink disease (Phytophthora cinnamomi ) eliminated them from the Gulf states in the early 1800s, and chestnut blight disease (Cryphonectria parasitica [Murr.] Barr) developed in the United States in the late 1800s. Ink disease probably came in on cork oak trees from Portugal, which were planted in the south before 1823. Blight disease was introduced in the 1880s, with Japanese chestnut planting stock. It spread up and down the eastern seaboard with nursery stock, and then moved into the forest by other vectors, until by 1950 almost all large chestnut trees were infected. Ink disease is lethal to chestnuts, but the blight fungus does not kill roots, so trees continue to sprout, are reinfected, and die back. There is good evidence that, in the southern United States, heavy shading, competition, grazing, and continued infections often kill the trees completely, but this is not the case in northern forests, where canopy type, competition, and predation are quite different.
In addition to the two diseases, chestnuts in the United States are also threatened by the Oriental Chestnut Gall Wasp (Dryocosmus kuriphilus ), another introduced pest that has become established and is damaging native chestnut species. The Gall Wasp is believed to have been introduced from Asia into Georgia in 1974 on scion wood that did not pass through proper quarantine. It infested orchards of Chinese chestnuts in Georgia and has also been found in wild trees of the American chestnut along the Appalachian Trail.
Procurement. Chestnuts are exported in large numbers from Italy, Spain, Australia, China, and Korea. Japan and the United States are primarily importers, although these markets are partially satisfied by locally grown chestnuts. New cultivars are being registered at an increasing rate, and interest in the crop is increasing.
Global and contemporary issues. The chestnut exemplifies both the dangers and benefits of globalization. The devastation of the North American forest by introduced diseases and insects argues in favor of the careful regulation of genetic materials moving between countries. Breeding programs are succeeding in developing resistance to these pests by the use of interspecific hybrids that were created using introduced germ plasm, illustrating the value of carefully sharing genetic resources.
Coconut (Cocos nucifera L.)
Plant biology. The coconut is a tall, tropical palm tree that reaches reproductive maturity six to ten years from planting and may live one hundred years. Tall varieties may reach heights of one hundred feet and have a single, usually curved or leaning, trunk with smooth gray bark marked by the ringed scars left by fallen leaf bases. A many-leafed crown tops the trunk, with each pinnately compound leaf being fifteen to twenty feet long. Male and female flowers are borne on a fleshy spike (spadix) enclosed within a leaflike sheath (spathe) arising from the leaf axils. Female flowers are in the basal position and male flowers are at the apex. Pollination may be either anemophilous (wind-distributed) or entomophilous (insect-distributed). The fruit is a large drupe eight to nine inches in diameter. The coconut has a thin, smooth, grayish brown epicarp, a one-to-three-inch-thick, fibrous mesocarp (yielding coir, a fiber used in thatching), and a woody endocarp (the shell). Inside the shell the endosperm comprises the single seed. A portion of the endosperm is solid (the flesh) and a portion is liquid (the milk). The coconut is light in relation to its volume, which allows it to float and be transported by water for long distances. Eventually it washes up on sandy, saline, tropical beaches where it is well adapted to survive. When the embryo germinates, the radicle emerges through one of three germinating pores visible on the outside of the shell. The three pores give the head-sized coconut the appearance of a monkey face. The genus name Cocos is derived from the Portuguese word for "monkey."
Coconut oil is extracted from the dried flesh, or copra, and is rich in lauric acid, a valuable antifungal, antiviral, and antiprotozoal compound. As a food, coconut oil is very high (86 percent) in saturated fats, which occur as medium-chain triglycerides that do not raise serum cholesterol or contribute to heart disease as much as long-chain triglycerides. Coconut oil is also a component of soaps and other health products.
History. Coconut fossils from the Tertiary period have been found in the Indo-Pacific Ocean region where the plant originated, and charred coconuts have been found in Western Melanesian archeological sites dated to 3000 b.c.e. The plant is a valuable source of food (the flesh), drink (the milk), and shelter (leaves, shell fibers, and trunk). In Sanskrit, the coconut palm is called "the tree which provides all the necessities of life." As a valued source of life's requirements, the coconut was spread by seafaring people throughout the Pacific, possibly as far as the Pacific coast of Central America, and west to India and East Africa. The first written mention of the tree was by an Egyptian monk in 545 c.e., and Marco Polo described coconuts growing in Sumatra, India, in 1280 c.e.
Procurement. Coconuts were first established in large-scale commercial plantations in the mid-nineteenth century, many from the seeds of local wild palms along the seashore. Planted coconuts now greatly outnumber wild palms, and coconut products form the main export of Ceylon, the Philippines, and other Indian and Pacific Ocean islands.
Hazelnuts (Corylus avellana L.)
Plant biology. Hazelnuts, also known as filberts, are produced on small, shrubby, often multitrunked trees that usually grow to heights of fifteen to twenty-four feet. They have simple, alternate, round-oval leaves with toothed margins. Hazelnuts are monoecious, with both male and female flowers on the same plant, but they are not self-fruitful. Flowers appear before the leaves. Male flowers are borne in catkins at nodes on one-year-old wood, and their wind-disseminated pollen is shed in midwinter. Female flowers are inconspicuous clusters of tiny flowers enclosed within bud scales, visible at the time of pollination as bright red stigmas extending from buds. Fruit matures from early September to October, with the ovoid or oblong nut inside a leafy husk. There is wide diversity in fruit and husk shape, and that diversity is reflected in the common names: "hazel" is from the Old English word for hood or bonnet (h æ sel ), which referred to a nut whose husk was shorter than the nut. "Filbert" is probably derived from the name of St. Philibert, a Frankish abbot whose feast day falls in the season when the nuts ripen; it has also been said that the name comes from "full beard," which referred to a long husk. In some countries long nuts are called "filberts," while shorter, round nuts are called "hazels."
The nuts are composed of a shell that has variable amounts of pubescence, especially at the tip. Inside the shell, the kernel is encased in a more-or-less-fibrous seed coat (pellicle) that is usually removed by blanching. Kernels are high in fat (62 percent), with the predominant being oleic acid (see Table 1). Hazelnut kernels are also high in Vitamin E, averaging 400 mg/100 g.
History. The European hazelnut was the first plant of the temperate deciduous forest to move into areas vacated by receding glaciers at the close of the last ice age, due primarily to its great climatic tolerance. Nuts are recovered at European archeological sites in conjunction with prehistoric human settlements, indicating a long history of food usage. Hazelnuts are one of Europe's oldest cultivated plants. They have been grown for centuries in Turkey, Italy, Spain, France, Germany, and England, although different conventions have arisen for their culture in each country. Hazelnuts were introduced in North America by shipments of seed sent in 1629 to the Massachusetts Company. Due to the eastern filbert blight (Anisogramma anomala [Peck] E. Muller), the culture of hazelnuts in the United States is concentrated in the coastal valleys of Oregon and Washington.
Procurement. In Turkey, the leader in world hazelnut production (65 percent), hazelnuts are cultured in traditional systems that rely on hand labor. Multitrunk seedling trees are planted in clumps of four or five bushes, often arranged irregularly on steep hillsides. Stems are progressively removed as they grow too old, allowing younger shoots to come into production. Nuts in the husk are hand harvested before the crop drops.
Italy follows Turkey in hazelnut production, accounting for about 23 percent of world production. Hazelnut culture in Italy is similar to that in Turkey, using clumps of multitrunk seedling trees, but with more uniform spacing. In Spain, where about 5 percent of world production originates, orchards are planted in still more regular rows, with a single bush at each location rather than a clump of separate bushes as in Turkey and Italy.
The United States produces about 3 percent of the world hazelnuts. In the United States, hazelnuts are grown in systems that facilitate mechanization and maximize nut size and yield per acre. Grafted trees of selected cultivars (mostly "Barcelona") are grown as single-trunk trees in evenly spaced rows, with about 200 trees per acre. Trees are sprayed with chemicals to accelerate and concentrate ripening. Nuts fall to the ground and are mechanically windrowed and harvested.
Global and contemporary issues. The European hazelnut, Corylus avellana, hybridizes with other species of Corylus that occur from China to the United States and that are largely untapped resources. The genetic diversity of the European hazelnut is well established, based on diverse seedling culture in the primary production centers. The potential is excellent for continued genetic improvement of hazelnuts through selection and breeding.
Peanuts (Arachis hypogaea L.)
Plant biology. The peanut (or groundnut) probably originated in South America although it was also cultivated in ancient China. It is a low-growing annual legume with subterranean fruits. Its leaves are stipulate and even-pinnate, mostly with two pairs of oval leaflets and no tendril. Flowers are formed in the axils of leaves and have a very long pedicel. Flowers are self-pollinated and usually do not open. After pollination, cell division in the pedicel drives the pod below ground, where it ripens. The fruit is an indehiscent, fibrous, constricted pod containing one to three dry edible seeds, each encased in a papery integument. The seeds are 20 to 25 percent carbohydrate, 25 to 30 percent protein, and 45 to 50 percent oil (see Table 1).
History. Peanuts may have been domesticated by selection from the related species Arachis monticola, found in northwest Argentina, and the only other member of the genus with the same chromosome number (4x 40), although other candidates are possible. Peanuts have been found in archeological sites in Peruvian desert oases dated to 2000 b.c.e. and were mentioned in Spanish historical records in 1550. Four major varieties of peanut form the foundations of world trade. "Virginia" prostrate peanuts were reported in the West Indies by the Spanish, and introduced from there into Mexico, as well as to West Africa via slaving ships. This variety was introduced to eastern North America from both the West Indies and West Africa in the seventeenth century. The Spanish took "Peruvian" prostrate peanuts from Peru to the Philippines and into southeastern China before 1600, with subsequent transport by Chinese traders. "Spanish" peanuts are an erect variety that is very high in oil. They were taken from Brazil to Africa in early introductions, and were established in Spain in the late eighteenth century. From Spain the "Spanish" peanuts were taken to southern France and were introduced in the United States in 1871. The "Valencia" was named for a location in Spain and introduced in the United States from that region about 1910. However, it had been introduced in Spain from Cordoba, Argentina, about 1900.
Procurement. Peanuts are grown worldwide in areas that have hot summers, alternating wet and dry seasons, and sandy soils. The plant is capable of fixing nitrogen in root nodules via symbiosis with the Rhizobium bacterium. Plants are harvested by digging and are piled to dry. In the United States, yields of over two tons per acre are often achieved. The major world producers of peanuts are China, India, and the United States (USDA–National Agricultural Statistics Service, 2001). The primary use for peanuts is as a source of edible oil, but they are also eaten as a food either boiled or dried. The tops of plants, as well as the residual protein-rich cake from oil extraction, can be fed to cattle.
Pecans (Carya illinoinensis [Wangenh.] K. Koch)
Plant biology. The pecan is a deciduous, temperate tree species native to North America. It is found in well-drained alluvial soils of the Mississippi River and its tributaries from Illinois and Iowa south to the Gulf Coast of Louisiana and west to the Edwards Plateau of Texas. Isolated populations are found as far east as southwestern Ohio, as far west as Chihuahua, Mexico, and as far south as Oaxaca, Mexico. In modern times, the distribution of pecans has been extended from the Atlantic seaboard west to California, with major commercial production in the non-native states of Georgia and New Mexico.
Trees are long-lived (to 300 years) and grow to heights of over 120 feet. Leaves are alternate, odd-pinnately compound, with nine to fifteen serrate leaflets. Trees are monoecious (male and female flowers are borne on the same tree) and dichogamous (male and female flowers mature at different times), a system that encourages out-crossing with other trees of a complementary bloom period. Male flowers are borne on pairs of three stalked catkins that arise from buds of the previous season. Female flowers are borne as spikes at the tip of the current season's shoots, usually with two to four flowers per spike. Pollen is disseminated by wind (anemophily). The fruit is a "drupelike nut," with the dehiscent husk splitting at maturity (usually September to December) to expose the elongated, relatively thin-shelled nut. Kernels are twolobed, separated in the shell by an internal partition or septum. Kernels are high in oil (70 percent), with the predominant oil being oleic acid (60 to 70 percent).
History. Some scientists think that early people carried pecan nuts north as the Laurentide ice sheet retreated at the close of the last ice age. Nuts have been found in Illinois in association with the artifacts of early people dated to around 8900 b.c.e. There is a rich history of pecan use by Native American tribes recorded in the writings of Hernando de Soto, Cabeza de Vaca, and Oviedo. Dense groves of native pecan trees growing along the Guadalupe River of Texas were visited every other year, due to the alternate-bearing cycle. In years of heavy production, pecans were a major component of people's diet.
Shell thickness and nut size were probably the two most important criteria of selection by early foragers, just as they are for modern pecan collectors. Trees producing large, thin-shelled nuts are more highly valued, more regularly visited, more extensively harvested, and (probably) more widely dispersed over time. About 1882, Edwin E. Risien of San Saba, Texas, offered a prize for the best native pecan. His intention was to obtain nuts from the prize-winning tree and plant them to establish an orchard of superior seedlings. The tree that won the competition came to be known as the "San Saba" pecan. Seedlings of that tree were selected and propagated, producing the "Western," "San Saba Improved," and "Onliwon" pecans, among others.
The first report of successful asexual propagation was by Abner Landrum in 1822. However, it was the gardener Antoine, a slave, who first established a commercially viable orchard by asexual propagation by grafting "Centennial" pecan on the Oak Alley Plantation in Louisiana in 1846. In the late 1800s several nurseries sold grafted trees, providing material for the first great boom in pecan orchard establishment, which occurred in Georgia in the early 1900s. The extensive acreage established at that time, largely using the "Stuart" cultivar, quickly moved Georgia to the lead in production of improved pecans.
Procurement. Native pecans are harvested from wild trees. Trees are often unmanaged except at harvest and yield less per acre and have lower-quality pecans than improved orchards. As a result, native pecans sell for less on the market. Land clearing for other crops greatly reduced native pecans during the last quarter of the twentieth century. Efforts to characterize and conserve the diversity of native pecans are being pursued.
Commercial pecans are grown in orchards of variable numbers of selected cultivars, grafted onto regionally adapted seedling rootstocks, in configurations that vary by geographic region. Tree density tends to increase from the East to the West, with many orchards planted on 50 50 spacings in the East, with 35 35 spacings common in Texas, and 30 30 spacing common in New Mexico and farther west. Cultivar diversity tends to be greatest in the Southeast, while many western orchards contain large blocks of a single cultivar, usually "Western." Grafted trees begin to bear between the fourth to eighth leaf, but may not achieve a positive cash flow until the twelfth to fifteenth leaf. Cost of culture varies by region, with increased cost for pesticide application in the Southeast, but increased irrigation expense in the arid West.
Pecans are the most important nut crop in Mexico, which has native as well as grafted orchards. Pecans are also grown to some extent in Israel, South Africa, Australia, Egypt, Peru, Argentina, Brazil, and China.
Global and contemporary issues. The United States is the world center of diversity for the pecan. As native trees are cleared, much of that diversity may be lost. Efforts are being made to collect and characterize the diversity of the pecan across its range and to establish appropriate in situ reserves.
Pine Nuts (Pinus cembroides Zucc.)
Plant biology. Pine nuts are produced by the piñon pine tree, a small-to medium-sized tree found at high elevations in the arid North American Southwest. Piñon is found from west Texas to California, north to Wyoming, and south into Chihuahua, Baja California, and Hidalgo, Mexico. Trees form broad pyramidal crowns and become round-topped with age. Trunks are often twisted and gnarled, with rough, irregularly furrowed bark. Typically there are two needles per fascicle, with needles being one to two inches long, sharp-pointed, and fragrant. Trees are monoecious, with male flowers produced as short staminate cones. Female cones are lateral or subterminal, about one to two inches long and almost as wide, and brown at maturity. Cones mature the second year, in August to September. The brown to black edible seeds are one-half to three-quarters of an inch long, triangular to ovate in shape, and often rounded at the base. They have a thin, brittle shell. The kernels are aromatic and flavorful, are rich in fat (61 percent), and have about 13 percent protein (see Table 1).
History. Pine nuts have been found in excavations at Gatecliff Shelter, Nevada, and dated at 6,000 years b.c.e. Nuts were used by Native Americans in the Southwest as an important component of their diet, both medicinally and ritualistically. The terminal buds, inner bark, and the core of green cones can be eaten in the spring. Several parts of the plant were used medicinally: crushed nuts for treatment of burns; pitch for treatment of wounds; smoke from burning branches for treatment of coughs, colds, and rheumatism; fumes of burning pitch for head colds, coughs, and earaches. Wood was used as fuel and in construction. Pitch was used for waterproofing, as a black dye, and as an adhesive. Ritualistically, the pitch was used by the Navajo to prepare corpses for burial, and by the Hopi, who painted it on their foreheads to protect them from sorcery.
Procurement. Most nuts are harvested from wild trees when the crop presents itself, which is irregularly. Traditionally, nuts are collected from the ground after the cones have opened. Piñon nuts have become regionally popular as an ingredient in specialty recipes, and the demand for nuts has been met by harvest practices that damage the tree, such as breaking off cone-bearing limbs. Once harvested, nuts store well and may be kept for up to three years without becoming rancid.
Pistachios (Pistacia vera L.)
Plant biology. Pistachios are members of the same family as the cashew nut, the Anacardiaceae (which also includes mango and poison ivy). Commercial pistachio nuts are produced by Pistacia vera, a deciduous tree that grows to a height of twenty-five to thirty feet, with alternate, pinnately compound leaves, each with three to five leaflets. Trees are dioecious, producing male flowers on some trees and female flowers on others. Both male and female flowers are borne on panicles in the axils of the previous year's growth. Pollen is spread by the wind to the apetalous female flowers. The fruit is a dry drupe with an outer hull and a dry, thin shell that splits upon drying to expose the greenish kernels, each usually about one inch long by one-half inch wide. Kernels have about 20 percent protein and over 50 percent fat, 65 percent of which is the monounsaturated fat oleic acid.
History. The pistachio tree probably originated in western Asia and Asia Minor, but grows wild eastward to Pakistan and India. Pistachios have been recovered from archeological excavations in Jordan, dated to 6760 b.c.e. The Jewish patriarch Jacob instructed his sons to carry pistachio nuts and almonds with them from their home in Palestine to Egypt, as gifts for their brother Joseph, when the family had to move during a period of extreme famine (New International Version Study Bible, Genesis 43:11). Pliny reported that pistachios were introduced to Italy from Syria during the first century b.c.e., and spread from there throughout the Mediterranean area.
Pistachios were first introduced to the United States around 1853–1854 by the commissioner of patents, who distributed seed for experimental purposes. The crop did not gain much interest until later introductions began to fruit, in about 1881. The cultivar "Kerman" was introduced in Chico, California, by USDA (United States Department of Agriculture) plant explorer W. E. Whitehouse in 1929, from collections made near Kerman, Iran. That cultivar is the basis of the California pistachio industry.
Procurement. The major pistachio-producing areas are Iran, Turkey, and the San Joaquin Valley of California. In Iran and Turkey, nuts are harvested from trees of improved cultivars growing in established orchards, but harvesting and processing methods are primitive. Nuts are harvested by hand and many are allowed to dry in the hull, which can stain portions of the shell red, making them unattractive. As a result, many imported nuts are dyed with a red vegetable dye to camouflage the stains. Pistachios produced in California are mechanically harvested, hulled, and dried, and are unstained. Technology ensures that they can usually be marketed in natural condition. Small, wild nuts with desirable green color are still harvested in Afghanistan, although destruction of forests by clearing, overgrazing, and producing charcoal has reduced wild populations.
Global and contemporary issues. International political issues have resulted in barriers to marketing pistachios, which has influenced domestic crop value and acreage planted.
Walnuts (Juglans regia L.)
Plant biology. Nuts from several species of the genus Juglans are consumed worldwide, but the most horticulturally important is the Persian walnut. Persian walnut trees grow to heights of seventy-five feet and have trunks with tight, silvery bark. Shoots have chambered pith, distinguishing Juglans from its sister genus Carya (which has a solid pith). Leaves are odd pinnately compound, with five to nine elliptic-ovate to long elliptic leaflets with entire margins, while black walnuts have more leaflets (fifteen to nineteen) that have serrate margins. Male flowers are borne laterally as single catkins on shoots of the previous season. Female flowers are borne terminally on current season shoots and usually have one to three nuts. Flowers are wind pollinated, and male and female flowers mature at different times of the season, promoting cross-pollination, which results in increased heterozygosity. Despite the predisposition to cross-pollinate, walnuts are self-fruitful. The fruit is a drupelike nut with a thick, irregularly dehiscent husk covering a shallowly fissured shell that encases the two kernels, each of which is deeply divided at the base.
Walnut kernels are rich in oils (64 percent), making them a high-energy food. The primary fatty acid is linoleic (62 percent), a polyunsaturated oil (see Table 1).
History. Progenitor trees were originally distributed across mountainous regions of central Asia, from eastern Turkey to Xin-jiang Province of western China. Walnuts have a long association with humans and have been found in archeological excavations of caves inhabited by prehistoric groups in China and the United States. Initial selection for large nut size and thin shell could have been unconscious, as seeds from unconsumed caches of preferred seed germinated and established seedlings near habitations. Over time, and in association with people, walnuts having large, relatively thin-shelled nuts were developed.
Improved walnuts were sent to Greece from Persia "by the kings," according to the Roman historian Pliny. From Greece, walnuts were introduced to Rome, where they were given the Latin name Jovis glans ('nut of Jupiter'), which was contracted to provide the genus name Juglans. The connection to Persian royalty is reflected in the specific epithet regia, meaning 'royal'. Romans spread walnuts throughout the Mediterranean, where the trees readily adapted to the warm, dry climate. The trees spread across Europe and into England where they became known in Old English as wealhhnutu (wealh means 'foreign' or 'strange', and hnutu means 'nut'). Although the tree is not capable of bearing profitable crops in the cool, wet English climate, it was esteemed for its high-quality wood. Walnuts were carried around the world in English ships, and came to be known in commerce as "English walnuts." Walnuts came to the United States with the first settlers in New England, although the first established production was from Spanish materials introduced in California.
Procurement. Walnuts are intensively cultured in California, with improved cultivars selected for high production and quality grafted onto hybrid rootstocks. Pollinizer cultivars are included to provide adequate cross-pollination. Orchards are irrigated, with up to five acre-feet of water per acre being required to mature a crop. Trees are chemically protected from pests, and mechanically harvested and processed.
In Europe and Asia, much production comes from seedling trees, with use of grafted cultivars increasing in Western Europe. Over centuries of cultivation, the selection of horticulturally valuable individuals and continued propagation by seed have resulted in distinct landraces in different regions.
Global and contemporary issues. In Europe, the economic incentive to increase production and quality by establishing monocultures of a few genotypes is being balanced by the awareness that regionally distinct land races provide a valuable source of genetic diversity. As more seedling trees are harvested for their valuable lumber, the need for conservation by in situ reserves has increased.
See also Fruit; Horticulture; Legumes; Vegetables.
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"Nuts." Encyclopedia of Food and Culture. . Encyclopedia.com. (May 22, 2018). http://www.encyclopedia.com/food/encyclopedias-almanacs-transcripts-and-maps/nuts
"Nuts." Encyclopedia of Food and Culture. . Retrieved May 22, 2018 from Encyclopedia.com: http://www.encyclopedia.com/food/encyclopedias-almanacs-transcripts-and-maps/nuts
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"nuts." A Dictionary of Food and Nutrition. . Encyclopedia.com. (May 22, 2018). http://www.encyclopedia.com/education/dictionaries-thesauruses-pictures-and-press-releases/nuts
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nuts / nəts/ • adj. inf. insane: the way he turns on the television as soon as he walks in drives me nuts. • interj. inf. an expression of contempt or derision: keep up the good work, and nuts to everyone who doesn't like it. PHRASES: be nuts about inf. like very much: I was nuts about him.
"nuts." The Oxford Pocket Dictionary of Current English. . Encyclopedia.com. (May 22, 2018). http://www.encyclopedia.com/humanities/dictionaries-thesauruses-pictures-and-press-releases/nuts
"nuts." The Oxford Pocket Dictionary of Current English. . Retrieved May 22, 2018 from Encyclopedia.com: http://www.encyclopedia.com/humanities/dictionaries-thesauruses-pictures-and-press-releases/nuts