Fruit

In botany, a fruit is the seed-bearing structure in flowering plants that is formed from the ovary after flowering.

Fruits are the means by which flowering plants (also known as angiosperms) disseminate their seeds. Edible fruits in particular have long propagated using the movements of humans and animals in a symbiotic relationship that is the means for seed dispersal for the one group and nutrition for the other; in fact, humans and many animals have become dependent on fruits as a source of food.[1] Consequently, fruits account for a substantial fraction of the world's agricultural output, and some (such as the apple and the pomegranate) have acquired extensive cultural and symbolic meanings.

In common language usage, "fruit" normally means the fleshy seed-associated structures (or produce) of plants that typically are sweet or sour and edible in the raw state, such as apples, bananas, grapes, lemons, oranges, and strawberries. In botanical usage, the term "fruit" also includes many structures that are not commonly called "fruits", such as nuts, bean pods, corn kernels, tomatoes, and wheat grains.[2][3]

Many common language terms used for fruit and seeds differ from botanical classifications. For example, in botany, a fruit is a ripened ovary or carpel that contains seeds; e.g., an apple, pomegranate, tomato or a pumpkin. A nut is a type of fruit (and not a seed), and a seed is a ripened ovule.[4] In culinary language, a fruit, so-called, is the sweet- or not sweet- (even sour-) tasting produce of a specific plant (e.g., a peach, pear or lemon); nuts are hard, oily, non-sweet plant produce in shells (hazelnut, acorn). Vegetables, so called, typically are savory or non-sweet produce (zucchini, lettuce, broccoli, and tomato); but some may be sweet-tasting (sweet potato).[5]

Examples of botanically classified fruit that typically are called vegetables include: cucumber, pumpkin, and squash (all are cucurbits); beans, peanuts, and peas (all legumes); corn, eggplant, bell pepper (or sweet pepper), and tomato, (see image). The spices chili pepper and allspice are fruits, botanically speaking.[4] In contrast, rhubarb is often called a fruit when used in making pies, but the edible produce of rhubarb is actually the leaf stalk or petiole of the plant.[6] Edible gymnosperm seeds are often given fruit names, e.g., ginkgo nuts and pine nuts.

Botanically, a cereal grain, such as corn, rice, or wheat is a kind of fruit (termed a caryopsis). However, the fruit wall is thin and fused to the seed coat, so almost all the edible grain-fruit is actually a seed.[7]

The outer layer, often edible, of most fruits is called the pericarp. Typically formed from the ovary, it surrounds the seeds; in some species, however, other structural tissues contribute to or form the edible portion. The pericarp may be described in three layers from outer to inner, i.e., the epicarp, mesocarp and endocarp.

Fruit that bears a prominent pointed terminal projection is said to be beaked.[8]

A fruit results from the fertilizing and maturing of one or more flowers. The gynoecium, which contains the stigma-style-ovary system, is centered in the flower-head, and it forms all or part of the fruit —(see graphic: 'the parts of a flower').[9] Inside the ovary(ies) are one or more ovules. Here begins a complex sequence called double fertilization: a female gametophyte produces an egg cell for the purpose of fertilization.[10] (A female gametophyte is called a megagametophyte, and also called the embryo sac.) After double fertilization, the ovules will become seeds.

Ovules are fertilized in a process that starts with pollination, which is the movement of pollen from the stamens to the stigma-style-ovary system within the flower-head, (see graphic). After pollination, a pollen tube grows from the (deposited) pollen through the stigma down the style into the ovary to the ovule. Two sperm are transferred from the pollen to a megagametophyte. Within the megagametophyte one sperm unites with the egg, forming a zygote, while the second sperm enters the central cell forming the endosperm mother cell, which completes the double fertilization process.[11][12] Later the zygote will give rise to the embryo of the seed, and the endosperm mother cell will give rise to endosperm, a nutritive tissue used by the embryo.

An apple is a simple fleshy fruit. Key parts are the epicarp, or exocarp, or outer skin, (not labelled); and the mezocarp and endocarp (labelled).
In the noni, flowers are produced in time-sequence along the stem. It is possible to see a progression of flowering, fruit development, and fruit ripening.

As the ovules develop into seeds, the ovary begins to ripen and the ovary wall, the pericarp, may become fleshy (as in berries or drupes), or it may form a hard outer covering (as in nuts). In some multiseeded fruits, the extent to which a fleshy structure develops is proportional to the number of fertilized ovules.[13] The pericarp typically is differentiated into two or three distinct layers; these are called the exocarp (outer layer, also called epicarp), mesocarp (middle layer), and endocarp (inner layer) —(see image of apple-section).

In some fruits the sepals, petals, stamens and/or the style of the flower fall away as the fleshy fruit ripens. However, for simple fruits derived from an inferior ovary —i.e., one that lies below the attachment of other floral parts, (see graphic re 'insertion point')— there are parts (including petals, sepals, and stamens) that fuse with the ovary and ripen with it. For such a case, when floral parts other than the ovary form a significant part of the fruit that develops, it is called an accessory fruit. Examples of accessory fruits include apple, rose hip, strawberry, pineapple; see below, and "Table of fleshy fruit examples".

Because several parts of the flower besides the ovary may contribute to the structure of a fruit, it is important to study flower structure to understand how a particular fruit forms.[3] There are three general modes of fruit development:

Consistent with the three modes of fruit development plant scientists have classified fruits into three main groups: simple fruits, aggregate fruits, and multiple (or composite) fruits.[14] The groupings reflect how the ovary and other flower organs are arranged and how the fruits develop, but they are not evolutionarily relevant as diverse plant taxa may be in the same group.

While the section of a fungus that produces spores is called a fruiting body,[15] fungi are members of the fungi kingdom and not of the plant kingdom.

Simple fruits are the result of the ripening-to-fruit of a simple or compound ovary in a single flower with a single pistil. In contrast, a single flower with numerous pistils typically produces an aggregate fruit; and the merging of several flowers, or a 'multiple' of flowers, results in a 'multiple' fruit.[16] A simple fruit is further classified as to whether it is dry or fleshy.

To distribute their seeds, dry fruits may split open and discharge their seeds to the winds, which is called dehiscence.[17] Or the distribution process may rely upon the decay and degradation of the fruit to expose the seeds; or it may rely upon the eating of fruit and excreting of seeds by frugivores —both are called indehiscence. Fleshy fruits do not split open, but they also are indehiscent and they may also rely on frugivores for distribution of their seeds. Typically, the entire outer layer of the ovary wall ripens into a potentially edible pericarp.

Fruits in which part or all of the pericarp (fruit wall) is fleshy at maturity are termed fleshy simple fruits.

Strawberry, showing achenes attached to surface. (Strawberries are not berries; they are classified as a dry simple fruit.)

Berries are a type of simple fleshy fruit that issue from a single ovary.[19] (The ovary itself may be compound, with several carpels.) The botanical term "true berry" includes grapes, currants, cucumbers, eggplants (aubergines), tomatoes, chili peppers, and bananas, but excludes certain fruits that are called "-berry" by culinary custom or by common usage of the term —such as strawberries and raspberries. Berries may be formed from one or more carpels (i.e., from the simple or compound ovary) from the same, single flower. Seeds typically are embedded in the fleshy interior of the ovary.

The strawberry, regardless of its appearance, is classified as a dry, not a fleshy fruit. Botanically, it is not a berry; it is an aggregate-accessory fruit, the latter term meaning the fleshy part is derived not from the plant's ovaries but from the receptacle that holds the ovaries.[22] Numerous dry achenes are attached to the outside of the fruit-flesh, (see image); they appear to be seeds but each is actually an ovary of a flower, with a seed inside.[22]

Schizocarps are dry fruits, though some appear to be fleshy. They originate from syncarpous ovaries but do not actually dehisce; rather, they split into segments with one or more seeds. They include a number of different forms from a wide range of families, including carrot, parsnip, parsley, cumin.[14]

An aggregate fruit is also called an aggregation, or etaerio; it develops from a single flower that presents numerous simple pistils (see graphic of raspberry pistils).[16] Each pistil contains one carpel; together they form a fruitlet. The ultimate (fruiting) development of the aggregation of pistils is called an aggregate fruit, etaerio fruit, or simply an etaerio.

Different types of aggregate fruits can produce different etaerios, such as achenes, drupelets, follicles, and berries.

For example, the Ranunculaceae species, including Clematis and Ranunculus, produces an etaerio of achenes;

Some other broadly recognized species and their etaerios (or aggregations) are:

The raspberry; its pistils are called drupelets because each pistil is like a small drupe attached to the receptacle. In some bramble fruits such as blackberry the receptacle, an accessory part, elongates and then develops as part of the fruit, making the blackberry an aggregate-accessory fruit.[25] The strawberry is also an aggregate-accessory fruit, of which the seeds are contained in the achenes.[26] Notably in all these examples, the fruit develops from a single flower, with numerous pistils.

A multiple fruit is formed from a cluster of flowers, (a 'multiple' of flowers) —also called an inflorescence. Each ('smallish') flower produces a single fruitlet, which, as all develop, all merge into one mass of fruit.[27] Examples include pineapple, fig, mulberry, Osage orange, breadfruit. An inflorescence (a cluster) of white flowers, called a head, is produced first. After fertilization, each flower in the cluster develops into a drupe; as the drupes expand, they develop as a connate organ, merging into a multiple fleshy fruit called a syncarp.

Progressive stages of multiple flowering and fruit development can be observed on a single branch of the Indian mulberry, or noni, (see image). During the sequence of development, a progression of second, third, and more inflorescences are initiated in turn at the head of the branch or stem.

For some fruits, some (or all) of the edible parts do not issue from the ovary; such fruit development can comprise all the pistils and other parts produced from one flower as well as all those produced from many flowers. This form of development is called accessory fruiting, and it occurs among all three classes of fruit development —simple, aggregate, and multiple. Accessory fruits are frequently designated by the hyphenated term showing both characters; e.g., pineapple is a multiple-accessory fruit.

Seedlessness is an important feature of some fruits of commerce. Commercial cultivars of bananas and pineapples are examples of seedless fruits. Some cultivars of citrus fruits (especially grapefruit, mandarin oranges, navel oranges), satsumas, table grapes, and of watermelons are valued for their seedlessness. In some species, seedlessness is the result of parthenocarpy, where fruits set without fertilization. Parthenocarpic fruit-set may (or may not) require pollination, but most seedless citrus fruits require a stimulus from pollination to produce fruit.[28] Seedless bananas and grapes are triploids, and seedlessness results from the abortion of the embryonic plant that is produced by fertilization, a phenomenon known as stenospermocarpy, which requires normal pollination and fertilization.[29]

Variations in fruit structures largely depend on the modes of dispersal applied to their seeds. Dispersal is achieved by wind or water, by explosive dehiscence, and by interactions with animals.[30]

Some fruits present their outer skins or shells coated with spikes or hooked burrs; these evolved either to deter would-be foragers from feeding on them, or to serve to attach themselves to the hair, feathers, legs, or clothing of animals, thereby using them as dispersal agents. These plants are termed zoochorous; common examples include cocklebur, unicorn plant, and beggarticks (or Spanish needle).[31][32]

By developments of mutual evolution the fleshy produce of fruits typically appeals to hungry animals, such that the seeds contained within are taken in, carried away and later deposited (i.e., defecated) at a distance from the parent plant. Likewise, the nutritious, oily kernels of nuts typically motivate birds and squirrels to hoard them, burying them in soil to retrieve later during the winter of scarcity; thereby, uneaten seeds are sown effectively under natural conditions to germinate and grow a new plant some distance away from the parent.[4]

Other fruits have evolved flattened and elongated wings or helicopter-like blades, e.g., elm, maple, and tuliptree. This mechanism increases dispersal distance away from the parent via wind. Other wind-dispersed fruit have tiny "parachutes", e.g., dandelion, milkweed, salsify.[30]

Coconut fruits can float thousands of miles in the ocean, thereby spreading their seeds. Other fruits that can disperse via water are nipa palm and screw pine.[30]

Some fruits have evolved propulsive mechanisms that fling seeds substantial distances —(perhaps up to 100 m in the case of the sandbox tree)— via explosive dehiscence or other such mechanisms, (see impatiens and squirting cucumber.[33]

A cornucopia of fruits —fleshy (simple) fruits from apples to berries to watermelon; dry (simple) fruits including beans and rice, coconuts and carrots; aggregate fruits including strawberries, raspberries, blackberries, pawpaw; multiple fruits such as pineapple, fig, mulberries; (see above re all)— are commercially valuable as human food. They are eaten both fresh and as jams, marmalade and other fruit preserves. They are used extensively in manufactured and processed foods (cakes, cookies, baked goods, flavorings, ice cream, yogurt, canned vegetables, frozen vegetables and meals) and beverages such as fruit juices and alcoholic beverages (brandy, fruit beer, wine).[34] Spices like vanilla, black pepper, paprika, and allspice are derived from berries. Olive fruit is pressed for olive oil and similar processing is applied to other oil bearing fruits/vegetables.[35]

Fruits are also used for socializing and gift-giving in the form of fruit baskets and fruit bouquets.[36][37]

Typically, many botanical fruits —"vegetables" in culinary parlance— (including tomato, green beans, leaf greens, bell pepper, cucumber, eggplant, okra, pumpkin, squash, zucchini) are bought and sold daily in fresh produce markets and greengroceries and carried back to kitchens, at home or restaurant, for preparation of meals.[38]

All fruits benefit from proper post harvest care, and in many fruits, the plant hormone ethylene causes ripening. Therefore, maintaining most fruits in an efficient cold chain is optimal for post harvest storage, with the aim of extending and ensuring shelf life.[39]

Various culinary fruits provide significant amounts of fiber and water, and many are generally high in vitamin C.[40] An overview of numerous studies showed that fruits (e.g., whole apples or whole oranges) are satisfying (filling) by simply eating and chewing them.[41] The dietary fiber consumed in eating fruit promotes satiety, and may help to control body weight and aid reduction of blood cholesterol, a risk factor for cardiovascular diseases.[42][43][44]

Fruit consumption is under preliminary research for the potential to improve nutrition and affect chronic diseases.[45][46] Regular consumption of fruit is generally associated with reduced risks of several diseases and functional declines associated with aging.[47][48][49]

For food safety, the CDC recommends proper fruit handling and preparation to reduce the risk of food contamination and foodborne illness. Fresh fruits and vegetables should be carefully selected; at the store, they should not be damaged or bruised; and precut pieces should be refrigerated or surrounded by ice.

All fruits and vegetables should be rinsed before eating. This recommendation also applies to produce with rinds or skins that are not eaten. It should be done just before preparing or eating to avoid premature spoilage.

Fruits and vegetables should be kept separate from raw foods like meat, poultry, and seafood, as well as from utensils that have come in contact with raw foods. Fruits and vegetables that are not going to be cooked should be thrown away if they have touched raw meat, poultry, seafood, or eggs.

All cut, peeled, or cooked fruits and vegetables should be refrigerated within two hours. After a certain time, harmful bacteria may grow on them and increase the risk of foodborne illness.[50]

Fruit allergies make up about 10 percent of all food related allergies.[51][52]

Because fruits have been such a major part of the human diet, various cultures have developed many different uses for fruits they do not depend on for food. For example: