Wayne's Word		Index		Noteworthy Plants		Trivia		Lemnaceae		Biology 101		Botany		Search

Not all nuts fit the above definition. In fact, Webster's New World Dictionary of the American Language (1970) also defines a nut as a foolish, crazy or eccentric person, or one of the two testicles in a male. Many so-called botanical nuts are more appropriately termed "drupes" or "dry drupes." These "false nuts" are really the seed-bearing, hard, inner layer (endocarp) of a fruit called a drupe. In dry drupes the outer layer or husk sometimes splits open or withers. This outer husk is part of the ovary wall (pericarp), and the hard inner wall surrounding the seed represents the inner part of the pericarp. Dry drupes are technically not true nuts because in true nuts the hard outer wall constitutes the entire pericarp. The coconut (Cocos nucifera) is a classic example of a dry drupe, with a thin, green, outer layer called the exocarp, a thick, fibrous middle layer called the mesocarp, and a very hard inner layer surrounding the large seed called an endocarp. These same three layers are easily visible in fleshy drupes such as the peach (Prunus persica), plum (P. domestica), and apricot (P. armeniaca). Unshelled almonds (P. amygdalus) are seeds still contained within an endocarp layer.

The pit of a peach (Prunus persica) showing the seed that is contained inside the hard, woody endocarp layer. The endocarp is the inner layer of the fruit wall or pericarp. It is surrounded by a fleshy mesocarp and a thin outer skin or exocarp. Fruits with a distinct endocarp layer surrounding the seed are called drupes. The endocarp protects and aids in the dispersal of the vulnerable seed, especially when it is swallowed by a hungry herbivore.

Other examples of drupes include date palm nuts (Phoenix dactylifera) and pistachio nuts (Pistacia vera). There is still considerable disagreement and controversy over the classification of some of these so-called nuts, particularly English walnuts (Juglans regia), black walnuts (J. nigra), and macadamia nuts (Macadamia integrifolia & M. tetraphylla). Botanists have devised all sorts of ingenious names for these "borderline nuts," such as dry drupe, drupe-like, drupaceous, drupaceous nut, and nutty drupe. Some readers may think the author of this essay has been driven to a mental condition with the same spelling as the plural of nut.

Pine nuts and pignolia nuts are seeds produced in woody cones from several species of pines, including the pinyon pines (Pinus monophylla & P. edulis), and the Italian stone pine (P. pinea).

The fruit of kukui nut or candlenut (Aleurites molucanna) is usually classified as a drupe or drupaceous nut, but the actual "nut" is really a woody, thick-walled seed, typically one or two inside each fruit. According to Spjut (1994), the kukui nut fruit is a "bacca" or berry-like fruit: An indehiscent simple fruit containing one or more seeds embedded in a solid, fleshy mass supported by epicarp less than 2 mm thick, the pericarp not differentiated internally by a hardened endocarp or air space. The tung oil fruit (A. fordii) appears to have a definite hard endocarp, so I am reluctant to call it a bacca. Goat nuts or jojoba are considered to be seeds within a dehiscent capsule. Brazil nuts (Bertholletia excelsa) are also seeds produced in a thick-walled capsule. The cashew nut (Anacardium occidentale) is a thick-shelled, seed-bearing drupe produced at the summit of a fleshy stalk (pedicel) called a cashew apple. According to Spjut (1994), the cashew fruit is called a "glans" and is similar to an acorn: An indehiscent fruit composed of a pericarp subtended or enclosed by a fruiting cupulate (aril-like) involucre that is derived from a swelling of bracts, receptacle or perianth. The peanut (Arachis hypogea) is actually a seed with a papery seed coat, typically two seeds enclosed in a dehiscent pod called a legume. After fertilization, the flower stalk of the peanut curves downward, and the developing fruit (legume) is forced into the ground by the proliferation and elongation of cells under the ovary. The peanut pod subsequently develops underground. Ivory-nuts are seeds from the ivory-nut palm (Phytelephas aequatorialis). Ivory-nut palms have an extensive distribution along banks of tropical American rivers, from Panama and Colombia to Peru. They are most abundant in the Amazon Basin of Bolivia, Ecuador and Peru. Female palms bear clusters of large, brown fruits, the size of grapefruits or melons. Each fruit is studded with numerous woody, pointed horns and contains four or more large seeds. The seeds are the source of vegetable ivory, a hard, natural material used as a substitute for elephant tusks.

Another interesting Malaysian "nut" that is actually a seed is called "buah keluak" or "kluwak nut" (also spelled kloowak). Kluwak nuts come from the kepayang tree (Pangium edule) of Indonesia & Malaysia, a member of the flacourtia family (Flacourtiaceae). The oily, hard-shelled seeds superficially resemble Brazil nuts. Meaty seeds are edible after the poisonous hydrocyanic acid is removed by soaking and boiling them in water. Fermented kluwak nuts become chocolate-brown, greasy and very slippery. Cooked seeds are used in a number of popular Malaysian and Indonesian dishes.

This bizarre horny fruit has two prominent, downcurved horns and superficially resembles the head of a bull. The fruit body has a woody, sculptured surface that resembles a face. To some people, the entire structure resembles a bat. It comes from an Asian aquatic plant often called "water caltrop" (Trapa bicornis). It is sometimes called water chestnut; however, this not to be confused with the crunchy, tuberous roots of a vegetable called water chestnut (Eleocharis dulcis) commonly served in Chinese restaurants. Other common names for this plant include Chinese horn nut and "ling kio" or "ling chio." It belongs to the water-caltrop family (Trapaceae) and includes the single genus (Trapa) with several closely-related species. The generic name Trapa is derived from calcitrappa, Latin name of the caltrop, in reference to the peculiar, horned fruits. During medieval times, a vicious weapon called a caltrop was used in European warfare. This was an iron device with four points so designed that one was always facing upward, whichever way it landed, to impale the hooves of enemy cavalry horses. A similar device was also used in World War II to destroy truck tires on enemy supply convoys. Actually, the widespread and more commonly-known water caltrop (Trapa natans) has a four-pronged fruit that more closely resembles the caltrop. The fruits of puncture vine also resemble a caltrop, especially when they impale your bicycle tires. In fact, this ubiquitous weed belongs to another unrelated plant family called the caltrop family (Zygophyllaceae).

Water caltrop plants are anchored to the bottom of lakes and ponds, and send to the surface a slender stem with a rosette of floating leaves. Like water hyacinths, the leaf stalks are inflated with air and are very buoyant. Solitary flowers are produced in the leaf axils followed by the strange horny fruits. Under the tough outer wall, the fruit contains a pulpy seed rich in starch. The fruits can be roasted or boiled like true chestnuts of the eastern United States. They are delicious sauteed with rice and vegetables. According to Joy Larkcom ("Oriental Vegetables," 1991), they contain toxins and should not be eaten raw. Seeds of some species are preserved in honey and sugar, candied, or ground into flour for making bread. In Italy Trapa natans is the main ingredient of a famous risotto (rice cooked in meat stock with shallots and butter). The unusual, bullhead pods of Trapa bicornis sometimes float down rivers and into the ocean where they occasionally drift ashore on Asian beaches. Local people make ingenious necklaces from the pods and sell them to tourists. With a backing attached to your lapel, they actually make a nice little emblem to wear on special occasions, or an attractive slide for a bolo tie.

According to Richard W. Spjut ("A Systematic Treatment of Fruit Types," Memoirs of the New York Botanical Garden Volume 70, 1994), the fruits of Trapa are classified as pseudodrupes." They are indehiscent with a thin, evanescent, fleshy exocarp and a persistent, stony endocarp. The English walnut (Juglans regia) it also classified as a pseudodrupe (see above). Richard Spjut also cites another complicated description of the fruit: "The so-called stone of Trapa (Trapaceae) includes part of the exocarp since the sepaloid horns are also hardened (Wildenow, 1811). If the pericarp itself is differentiated into soft and hardened (stone) layers, excluding the exocarp, the fruit is then a pome."

Some "nuts" are actually large, hard-shelled seeds produced inside a dehiscent capsule that splits open into sections called valves or carpels. The buckeye (Aesculus) is a good example of this kind of nutlike seed. There are several species of buckeye, including the California buckeye (A. californica), Ohio buckeye (A. glabra), and the European horse chestnut (A. hippocastanum), all members of the horse chestnut family (Hippocastanaceae). Another hard-shelled seed called Texas buckeye (Ungnadia speciosa), belongs to the interesting soapberry family (Sapindaceae).

The outer capsule wall of the European horse chestnut (Aesculus hippocastanum) is covered with stout spines. They are collected in autumn and the large seeds are removed from the spiny casing and allowed to dry. In England, the dried, hard-shelled seeds are used in a curious children's game called "conkers." A hole is drilled through the seed (called a conker) and a string in threaded through the hole. The game is played between two opponents, each with one conker. One player dangles their conker by the string, holding it steady, while the opponent swings their conker on its string and attempts to strike the dangling conker. Players take turns until one conker is so badly damaged that it dislodged from its string. The winner is the player with the intact conker. Serious conker players try to harden the shell (seed coat) of their conker by drying techniques and various protective finishes. In Australia, a similar game is called "bullies." One of the choice seeds used for this game comes from the fruit of the quandong tree (Eucarya acuminata), a member of the sandalwood family (Santalaceae). Like the Hawaiian sandalwood (Santalum), this tree is a root parasite on a nearby host plant.

Return To Economic Plant Families Page Return To WAYNE'S WORD Home Page Return To NOTEWORTHY PLANTS Page Go To Biology GEE WHIZ TRIVIA Page Go To The LEMNACEAE ON-LINE Page