Fruit

• 1. Introduction

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  A strawberry is not a berry. A banana is. The tomato hiding in a savory salad is, botanically, a fruit and a berry both, while the strawberry that crowns a dessert is technically a dry fruit. In botany, a fruit is the seed-bearing structure of flowering plants, the angiosperms, formed from the ovary after a flower blooms. That single definition quietly sweeps in things no shopper would ever call fruit. Nuts, bean pods, corn kernels, and wheat grains all qualify. So how can a coconut, a peanut, and a grain of rice belong to the same family of structures as an apple? Why does the language of the kitchen disagree so sharply with the language of the laboratory? And how did these structures convince humans and animals to carry their seeds across the world? The answers begin inside the flower, where a process called double fertilization sets everything in motion.

• 2. Two Languages For One Thing

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  An orange, a pomegranate, a tomato, and a pumpkin are all the same kind of object to a botanist: a ripened ovary or carpel that contains seeds. A nut, in this strict view, is a type of fruit and not a seed at all, while a seed is a ripened ovule. The kitchen sorts the world differently. There, a fruit is the sweet, not-sweet, or even sour produce of a plant, like a peach, pear, or lemon. Nuts become the hard, oily, non-sweet produce in shells, such as hazelnut or acorn. Vegetables cover the savory or non-sweet produce like zucchini, lettuce, broccoli, and tomato, though a few, like sweet potato, taste sweet. The overlap creates a long list of impostors. Cucumber, pumpkin, and squash are botanical fruits called vegetables; so are beans, peanuts, and peas, all legumes, and corn, eggplant, bell pepper, and tomato. Many spices join the list, including black pepper, chili pepper, cumin, and allspice. Rhubarb runs the opposite way: bakers treat it as fruit in pies, but the edible part is the leaf stalk, the petiole. Even a grain of wheat or rice is a fruit, a type called a caryopsis, though its wall is so thin and fused to the seed coat that nearly all the edible grain is actually seed.

• 3. Inside The Ovary

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  Double fertilization is the strange, ancient choreography that turns a flower into a fruit. At the center of the flower-head sits the gynoecium, the stigma-style-ovary system, and inside the ovary lie one or more ovules. It begins with pollination, the movement of pollen from the stamens to the stigma. A pollen tube then grows down through the stigma and style into the ovary, reaching the ovule. Two sperm travel through that tube to the megagametophyte. One sperm unites with the egg to form a zygote; the second enters the central cell to form the endosperm mother cell. The zygote becomes the embryo of the seed. The endosperm mother cell becomes endosperm, a nutritive tissue the embryo will feed on. This entire sequence is bound up with meiosis, the dividing of cells that underlies sexual reproduction in flowering plants. Homologous chromosomes replicate, recombine, and segregate, producing haploid cells whose union yields a diploid zygote. In some multi-seeded fruits, the more ovules that get fertilized, the more fleshy structure develops. As the ovules ripen into seeds, the ovary wall, the pericarp, begins to mature into the fruit itself.

• 4. The Architecture Of A Fruit

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  The pericarp is the outer layer, often edible, that surrounds the seeds of most fruits. It can be read in three layers from outside in: the epicarp or exocarp, the mesocarp in the middle, and the endocarp within. In a berry or a drupe that wall turns fleshy; in a nut it hardens into a tough covering. A fruit that carries a prominent pointed projection at its tip is described as beaked. The flower does not always vanish cleanly as the fruit forms. In some species the sepals, petals, stamens, or style fall away, but when the ovary is inferior, sitting below the attachment of the other floral parts, those parts can fuse with the ovary and ripen alongside it. When such non-ovary parts make up a significant share of the fruit, the result is an accessory fruit. The apple is one. So are the rose hip, the strawberry, and the pineapple. Because parts of the flower besides the ovary can build the final structure, fruits fall into three developmental modes: apocarpous fruits from a single flower with separate carpels, syncarpous fruits from a single gynoecium of fused carpels, and multiple fruits from a whole inflorescence of flowers.

• 5. Simple, Aggregate, And Multiple

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  Plant scientists sort fruits into three main groups that mirror those three modes: simple fruits, aggregate fruits, and multiple or composite fruits. The groupings describe how the ovary and flower organs are arranged, but they are not evolutionarily meaningful, since very different plant taxa can share a group. A simple fruit ripens from a single or compound ovary in one flower with a single pistil, and it is either dry or fleshy. Dry simple fruits cover a remarkable range: the achene seen in strawberries, the capsule of the Brazil nut, the caryopsis of cereal grains, the legume of bean, pea, and peanut, the nut of the beechnut, hazelnut, and acorn, and the winged samara of ash, elm, and maple. Fleshy simple fruits include the berry, the drupe or stone fruit with its hard lignified pit found in apricot, cherry, olive, peach, plum, and mango, and the pome of apples and pears, which develops from a half-inferior ovary in the family Rosaceae. An aggregate fruit, also called an etaerio, develops from a single flower with many simple pistils, as in the raspberry, whose pistils form small drupelets attached to the receptacle. A multiple fruit like a fig or mulberry forms from a whole cluster of flowers, each producing a fruitlet that merges into one mass. One caution sits at the edge of this scheme: the spore-producing part of a fungus is called a fruiting body, but fungi belong to the Fungi kingdom, not the plant kingdom.

• 6. The Berry Paradox

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  Grapes, currants, cucumbers, eggplants, tomatoes, chili peppers, and bananas are all true berries, a fact that overturns most kitchen intuition. A true berry is a simple fleshy fruit that issues from a single ovary, with seeds embedded in the fleshy interior. The banana has been described as a leathery berry, and in cultivated varieties its seeds shrink nearly to nothing. Specialized berries carry their own names: the pepo, a berry with a hardened skin, covers the cucurbits like gourds, squash, and melons, while the hesperidium, a berry with a rind and juicy interior, describes most citrus. The strawberry breaks every expectation here. Despite its look, it is classified as a dry fruit, not a fleshy one, and it is not a berry at all. It is an aggregate-accessory fruit, meaning the fleshy part comes not from the ovaries but from the receptacle that holds them. The specks on its surface that look like seeds are actually dry achenes, each one an ovary with a seed inside. Schizocarps add another twist: they look fleshy to some eyes but are dry, splitting into segments rather than bursting open, and they include carrot, parsnip, parsley, and cumin.

• 7. How Fruits Travel

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  A sandbox tree can fling its seeds perhaps up to 100 meters through explosive dehiscence, one of nature's most violent dispersal tricks. Variations in fruit structure trace back largely to how a plant moves its seeds, whether by wind, water, explosion, or animals. Some fruits coat their skins with spikes or hooked burrs, like cocklebur, unicorn plant, and beggarticks, to snag the hair, feathers, legs, or clothing of passing animals; these are termed zoochorous. The fleshy, appealing fruits take a gentler route, tempting hungry animals to swallow the seeds and deposit them at a distance. The oily kernels of nuts push birds and squirrels to bury them as winter stores, and the forgotten ones germinate far from the parent. Wind carries others: elm, maple, and tuliptree grow flattened wings or helicopter blades, while dandelion, milkweed, and salsify ride tiny parachutes. Coconut fruits float across the ocean, as do nipa palm and screw pine. The burdock and cocklebur did more than scatter seeds. Their spiny fruit inspired the invention of Velcro.

• 8. Beyond The Plate

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  Fruit allergies account for about 10 percent of all food-related allergies, a reminder that even staple foods carry risk. Fruits sit at the heart of the human diet, eaten fresh and turned into jams, marmalade, juices, and alcoholic drinks like brandy, fruit beer, and wine. Spices such as vanilla, black pepper, paprika, and allspice come from berries, and olive fruit is pressed for oil. A meta-analysis of 83 studies linked fruit or vegetable consumption to reduced markers of inflammation, including lower tumor necrosis factor and C-reactive protein, and to an enhanced immune profile with increased gamma delta T cells. The dietary fiber in fruit promotes satiety and may help control weight and lower blood cholesterol. Many fruits never reach a plate at all. Bayberry fruits yield a wax for candles, and the opium poppy's fruit produces opium, the source of codeine, morphine, and the thebaine from which oxycodone is synthesized. Osage orange fruits repel cockroaches; cherry, mulberry, sumac, and walnut give natural dyes. Pumpkins become Jack-o'-lanterns at Halloween, the dry Luffa fruit's fibrous core becomes a sponge, and the hard, colorful grains of Job's tears are strung as decorative beads for jewelry and ritual objects.