BOTANY. PLANT MORPHOLOGY - O. A. Shevchuk - 2014

FRUIT MORPHOLOGY

Following Fertilization, the pistil's Ovary develops into a fruit, while the ovules, which transform into seeds, reside within the fruit. The fruit protects the seeds from physical damage and other adverse environmental factors, and also serves as the reproductive and dispersal organ for plants.

A fruit consists of the pericarp and the seed. As noted, the seed develops from the ovule, the pericarp from the ovary wall, and the fruit stalk from the pedicel. In almost all plants, the seed remains enclosed by the pericarp until maturity; upon ripening, the pericarp splits open in some plants to release the seeds. Accordingly, fruits are classified into dehiscent and indehiscent.

The pericarp consists of three layers: the exocarp, mesocarp, and endocarp. The outer layer, the exocarp, develops from the outer epidermis of the ovary wall. The exocarp may bear a cuticle, hairs, a bloom, and other structures. The inner epidermis gives rise to the inner pericarp layer, the endocarp. Its Structure varies among plant species. In stone fruits (such as plum, peach, and cherry plum), the endocarp comprises a layer of lignified Cells known as sclereids, commonly referred to as the stone or pit. Enclosed within the stone, the seed is reliably protected from adverse conditions, enabling the embryo to remain viable for a long time. The consistency and STRUCTURE OF THE endocarp vary; it is membranous in apples and pears, and fibrous in pumpkins. The pericarp layer situated between the exocarp and endocarp forms the middle portion, termed the mesocarp. Often, the mesocarp enlarges, becoming fleshy and succulent, thereby forming a succulent fruit. Together, the three pericarp layers (exocarp, endocarp, and mesocarp) constitute the pericarp.

By the time the fruit ripens, the pericarp remains dry in some plants, whereas in others it becomes succulent. Consequently, fruits are distinguished as dry and succulent.

Modern morphogenetic classifications of fruits are based on the structure and evolution of well-known gynoecium types: apocarpous, syncarpous, paracarpous, and lysicarpous. Depending on the gynoecium type and placentation, fruits are categorized as apocarpous, syncarpous, paracarpous, and lysicarpous. The morphogenetic Classification also takes into account THE POSITION OF the ovary (superior or inferior) and certain other traits.

Quite frequently, other floral parts (stamen bases, petals, sepals, and less commonly the receptacle) also participate in fruit formation, which is clearly observed when a fruit develops from an inferior ovary (such as in pomegranate, pear, apple, pumpkin, and cucumber). In strawberries, the succulent portion of the fruit develops from the greatly enlarged receptacle.

Many plants produce fruit and seeds only once during their ontogeny and subsequently die. These are known as monocarpic plants. They include annuals (pea, sunflower, millet, etc.), biennials (carrot, cabbage, beet, etc.), and perennials (agave, bamboo, etc.). An interesting group of monocarpic plants comprises certain perennial tropical herbs. The American agave lives for up to 100 years and dies after flowering and fruiting. Plants that repeatedly produce seeds and fruits throughout their ontogeny are termed polycarpic. All fruit and forest woody plants in our region are polycarpic. Most perennial herbaceous plants also belong to this group. Remontant plants are capable of flowering and fruiting multiple times during a single growing season (certain varieties of strawberries and raspberries).

The Morphology of fruits in flowering plants is exceptionally diverse. This variety stems from the immense number of taxonomic groups of angiosperms and the adaptation of fruits to their dispersal agents, which significantly complicates the establishment of a universal fruit classification. The morphological classification of fruits is very popular and widely used. Fruits are broadly divided into simple, aggregate (multiple), and collective (infructescence) fruits.

Simple fruits develop from a simple apocarpous or coenocarpous gynoecium—that is, only a single pistil takes part in their formation. They can be dehiscent, indehiscent, fragmenting, articulated, dry, or succulent.

A fruit formed by several pistils of a single flower is called an aggregate or multiple fruit.

The morphological and ecological classification of simple and aggregate fruits is based on the following features: pericarp consistency (dry or succulent); seed number (single-seeded or many-seeded); mode of pericarp dehiscence (indehiscent, dehiscent, fragmenting, and the specific mechanism of opening); and the number of carpels forming the fruit.

Dry fruits

They can be dehiscent or indehiscent, single-seeded or many-seeded. Dry fruits are those in which the moisture content of the pericarp is up to 15%.

Dehiscent many-seeded dry fruits (capsular fruits)

Follicle — develops from a single carpel, typically many-seeded, and opens along a single suture—the ventral (front) suture. The opened fruit resembles a leaf. It occurs in certain Ranunculaceae, larkspur, and globe thistle.

Legume (pod) — develops from a single carpel, is one- or many-seeded with seeds arranged in a single row, and opens along two sides—the ventral (front) and dorsal sutures. This is characteristic of members of the Fabaceae family. Legumes may be articulated (in sweet vetch), spirally twisted (alfalfa), or single-seeded and indehiscent (sainfoin).

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Fig. 20. Capsular fruits: A - follicle in marsh marigold, Magnoliaceae, some Ranunculaceae, Rosaceae; B - aggregate follicle in columbine; C - legume in pea; D - silique in cabbage; E - articulated silique in radish; F - silicle in shepherd's purse; G - capsule in poppy; H - in henbane; I - in jimsonweed.

Silique — develops from two carpels that form a single pistil; the length of the fruit exceeds its width by 4 times or more. It is bilocular, many-seeded, with seeds attached along the margin of a false septum. It dehisces bilaterally (along both sides of the partition) from bottom to top (cabbage, turnip, stock, and other Brassicaceae). Siliques can be articulated (wild radish), breaking transversely into individual single-seeded segments.

Silicle — has a structure similar to a silique but differs in that its length equals its width or exceeds it by no more than 2-3 times (shepherd's purse, pennycress). It may be dehiscent (shepherd's purse, pennycress) or indehiscent (woad).

Capsule — depending on the number of carpels, it may be bilocular or multilocular. Sometimes, regardless of the number of carpels, the capsule is unilocular, as in poppy (7-11 carpels) and Caryophyllaceae (5 carpels). It dehisces by various mechanisms: by lids (henbane), by pores (poppy), by Valves along the sutures (cotton), by Teeth (Caryophyllaceae), or by valves (jimsonweed).

Indehiscent single-seeded dry fruits (nut-like fruits)

Nut, nutlet — a simple fruit with a woody, stone-like pericarp, developing in most cases from one, and occasionally 2-3 carpels. It is single-seeded, with the seed lying loose inside the closed pericarp and not fused to it. A nutlet (buckwheat) differs from a nut (hazel) in its smaller size and leathery pericarp.

Based on its structure, the oak acorn can be classified into this group. Unlike a nut, an acorn sometimes develops from three carpels. The cupule (or cup), which serves as a protective covering, is formed from enlarged and lignified bracts. Oak acorns are enclosed in a cup-shaped cupule, whereas the nutlets of beech and chestnut each grow inside spiny cupules. In addition, in chestnut and beech, 3-4 nutlets are surrounded by a common cupule.

Fig. 21. Nut-like fruits: A - nut - in hazel; B - nutlet - in buckwheat, linden; C - caryopsis - in wheat; D - acorn - in oak; E - samara - in elm; F - small samara - in maple; G - achene - in sunflower, dandelion, chamomile; H and I - aggregate nutlet (H - buttercup, I - strawberry).

Achene — differs from the nut and nutlet by having a softer, leathery pericarp. An achene develops from two carpels, is indehiscent and one-seeded, and the seed is free and not fused with the pericarp. It is widespread in Asteraceae and Valerianaceae. In many Asteraceae, the achene features a pappus, known as a flier. In beggarticks, appendages and hooks form on the achene. All these structures facilitate the dispersal of the achene.

Samara — corresponds to an achene whose pericarp has a leathery or membranous wing-like appendage. A distinction is made between a single samara (ash) and a double samara. A double samara consists of two one-seeded fruitlets with winged outgrowths (species of the genus maple — Acer).

Caryopsis — formed As a result of the fusion of the seed coat with the pericarp, developed from two carpels, one-seeded, and characteristic of Poaceae (wheat, barley, corn, oats, etc.).

Schizocarpic fruits (or schizocarps), which break down into separate segments, are evolutionarily more advanced compared to dehiscent fruits. They are divided into aggregate (di-achenes: dill, carrot; double samara: maple) and loments (wild radish). Schizocarpic fruits are found in representatives of Lamiaceae and Boraginaceae.

Succulent fruits

Succulent fruits develop from one or several carpels. Their pericarp contains more than 15% hygroscopic moisture.

Berry-like fruits

Berry — develops from one or several carpels, many-seeded, with seeds embedded in a succulent pericarp (grape, gooseberry, currant, tomato, eggplant, nightshade, persimmon, etc.). In some plants, such as gooseberry and currant, the succulent part of the berry is formed not by the pericarp, but by the succulent seed coats. The pomegranate has a very peculiar fruit structure: the pericarp forms a leathery outer layer and membranous partitions developing from the ovary, while the succulent part is the seed coat derived from the integuments.

Pepo — a specialized type of berry formed from an inferior ovary; it is a succulent, many-seeded fruit derived from three carpels. The exocarp is hard, and only the endocarp is succulent. It is characteristic of Cucurbitaceae (pumpkin, cucumber, melon, watermelon, etc.).

Pome — a false fruit that develops from a five-chambered inferior ovary (five carpels); In addition to the ovary, the bases of sepals, petals, and other floral parts participate in fruit formation. In the pome fruit, the endocarp becomes relatively hard and leathery, enclosing chambers with two freely lying seeds. The pome fruit is characteristic of apple, pear, quince, etc.

Hesperidium — a multilocular, many-seeded succulent fruit with a colored exocarp containing essential oil glands, while the mesocarp is dry, spongy, and white. The succulent part of the fruit is formed by the endocarp — the overgrown hairs of the inner epidermis of the ovary that transform into juice sacs. It is characteristic of citrus plants (lemon, orange, tangerine).

Pomegranate — a fruit formed by an inferior ovary composed of four fused carpels. The fruit Skin itself is quite leathery, colored, and poorly differentiated into exocarp, mesocarp, and endocarp. Its fleshy and succulent part consists of the outer layer of the seed coat surrounding each of the many seeds that fill the leathery, multi-chambered fruit.

Banana — a many-seeded fruit derived from three carpels with an inferior ovary, featuring a leathery and relatively thick exocarp, while both inner layers form a succulent, starchy pulp. Cultivated forms are predominantly seedless.

Fig. 22. Berry-like fruits: A-C - berry - in grape, B - in potato, C - in banana, D - pome - in apple, E - hesperidium - in orange, F - pepo - in cucumber, watermelon, melon.

Drupaceous fruits

Drupe — a succulent fruit in which the pericarp is clearly differentiated into exocarp, mesocarp, and endocarp. The endocarp is multi-layered and lignified, forming the stone (pit). It occurs predominantly in Rosaceae (peach, apricot, plum, cherry plum, blackthorn, etc.). The succulent part of the drupe is the mesocarp of the pericarp. Based on the type of gynoecium, several types of drupes are distinguished.

Fig. 23. Drupaceous fruits: A, B - drupe [A - in plum (Prunus domestica)]; C - cross-section of a flower and aggregate drupe - in raspberry (Rubus idaeus): 1 - exocarp, 2 - mesocarp, 3 - endocarp, 4 - seed.

Apocarpous drupe (monodrupe) — a one-seeded fruit developing from a single carpel (cherry, plum, apricot, peach). Guelder rose and dogwood possess a coenocarpous single-stone drupe, whereas elderberry and buckthorn are characterized by a coenocarpous multi-stone drupe. Depending on The Nature of the pericarp, a drupe can be dry or succulent. In walnut and almond, the fruit is a dry drupe, formed from an inferior ovary fused with the receptacle and calyx. After fruit ripening, the mesocarp and exocarp of this dry drupe separate from the leathery (almond, walnut) or fibrous (coconut palm) endocarp.

The group of fruit-bearing plants that produce a drupe fruit is referred to as stone fruit crops.

Other fruit types

An aggregate fruit develops from a flower with multiple pistils (an apocarpous gynoecium). In columbine, the fruit is an aggregate follicle (multiple follicle). In strawberries, the juicy part is formed by an enlarged receptacle bearing numerous dry fruits known as achenes. Thus, the strawberry fruit is juicy and is referred to as an aggregate achene. A somewhat similar fruit structure is characteristic of the lotus, in which nutlets are embedded into the fleshy, enlarged receptacle tissue. This type of fruit can be called an aggregate nutlet with a fleshy receptacle. An etaerio (aggregate drupe, multiple drupe) is an apocarpous fleshy fruit formed by a collection of drupes situated on a common elongated, convex receptacle (e.g., raspberry, blackberry, etc.).

Fig. 24. Inflorescence and multiple fruit of the mulberry: A - inflorescence of pistillate flowers, B - pistillate flower, C - multiple fruit; D - one of the fruits in longitudinal section.

Multiple fruit (infructescence). In some plants, an inflorescence develops into a multiple fruit (mulberry, fig, beet, spinach, pineapple, etc.). A multiple fruit is formed when individual fruitlets—each originating from a separate flower in a dense inflorescence—grow together. In primitive multiple fruits, individual fruitlets sit on separate pedicels (grape, elderberry, rowan). In specialized multiple fruits, the naked fruitlets fuse together. In addition to the pistil, other PARTS OF THE inflorescence participate in The formation of multiple fruits: the enlarged perianth (mulberry); the enlarged inflorescence axis (fig); and the enlarged inflorescence axis combined with bracts (pineapple).

The Development of two or more embryos within a single seed is called polyembryony. Polyembryony occurs in citrus fruits, onions, etc. In twin-embryo formation, one embryo develops from the primary egg Cell, while the other arises from a suspensor cell. Sometimes the number of embryos in a single seed reaches 20 (mandarin orange), the majority of which are formed via apomixis from nucellar cells. Such embryos are called nucellar embryos.

The development of fruit without seed formation is called parthenocarpy. Parthenocarpy should not be confused with parthenogenesis (the development of an embryo without fertilization). In parthenocarpy, a seedless fruit can form regardless of whether fertilization has taken place. Parthenocarpic fruits include seedless grape cultivars, seedless persimmons, seedless pears, and seedless fig infructescences, among others. Parthenocarpic fruit plants propagate exclusively by vegetative means. Obtaining seedless fruits is associated with considerable difficulties and remains one of the most fascinating problems in pomology and fruit growing.

Two forms of parthenocarpy are observed: vegetative and stimulative. In the first case, the fruit forms prior to or without pollination (seedless pear). Stimulative parthenocarpy occurs when the stigma of the pistil is irritated by stimulants. Mature, related pollen is frequently used as a stimulant; for example, pollinating apple blossom stigmas with pear pollen, pepper with potato pollen, or plum with apricot pollen, among others. Parthenocarpy can also be induced by irritating stigmas with chemical Reagents, a weak electric current, or irradiation.

Some plants exhibit geocarpy—the development and ripening of fruits where the ovary, following fertilization, burrows into the soil, where fruit formation subsequently takes place (e.g., peanut, stork's bill, feather grass).

Dispersal of Seeds and Fruits

The formation of fruits on the above-ground shoots of plants is called aerocarpy. Fruit formation at the apex of a SHOOT is termed acrocarpy. The falling of fruits and seeds under METABOLISM/18.html">The Influence of gravity is referred to as barochory.

External factors—such as Water, wind, animals, and humans—participate in the Dispersal of fruits and seeds. The dispersal of plant fruits and seeds via external agents is called allochory. In herbaceous plants of tropical rainforests (epiphytes), the seeds are so lightweight that they are carried over long distances even by negligible air currents—anemochory. Seeds are also dispersed by wind via pappus structures (Asteraceae), wing-like appendages (maple, birch, poplar), or air cavities (lotus).

The dispersal of fruits, seeds, and spores by animals is called zoochory. Several types of zoochory are distinguished: epizoochory, a dispersal mechanism where fruits, seeds, and spores are transported by animals to which they attach via various appendages. In many steppe and meadow plants, the seed coat bears small barbs (anchor-like hooks) and prickles (e.g., cocklebur), which cling to animal fur and human clothing, carrying the seeds over considerable distances. Endozoochory involves animals and birds consuming fruits with juicy, nutritious pericarp and dispersing the seeds via excrement. Passing through the digestive tract of animals and birds, the seeds retain their viability, and thanks to a tough seed coat, they exit the Organism undamaged. Synzoochory is a type of dispersal where animals collect and transport fruits, seeds, and spores to new locations. Myrmecochory is the dispersal of fruits, seeds, and spores by ants (violet, lungwort, etc.). Ants are exceptional seed dispersal agents, transporting seeds bearing edible surface appendages—known as caruncles or arilodes—over significant distances. Outgrowths on seeds and fruits that accumulate oils and facilitate insect-mediated dispersal are called elaiosomes (found in certain species of greater celandine and wood-rush). Ornithochory is seed, fruit, and spore dispersal by birds (Siberian pine, guelder rose, rowan, etc.). Mammaliochory is the dispersal of fruits and seeds by mammals (beggar-ticks, burdock, etc.).

Fruits and seeds of aquatic and wetland plants are dispersed by water—hydrochory (sedges, water lilies).

Upon seed maturation, many desert and semi-desert plants detach from the ROOT and are driven by the wind, tumbling along (as "tumbleweeds") and scattering seeds as they move. Many plants (vetch, bean, lupine, Touch-me-not, squirting cucumber) exhibit autochory—the dispersal of fruits, seeds, and spores through specialized mechanical adaptations without the Influence of External agents. The fruits of certain plants violently eject their seeds upon dehiscence—mechanochory. However, the distance to which seeds are forcibly thrown typically does not exceed 10–20 cm, making this dispersal method far less effective than others.

The most active disperser of seeds and fruits is humankind (anthropochory). Not only do humans deliberately transport plant seeds to every corner of the globe, but they also contribute to their accidental dispersal (for instance, when military units move, soldiers inadvertently carry seeds from one region to another on their clothing and boots).

Some plants exhibit heterocarpy, developing fruits of different shapes and physiological properties with distinct dispersal mechanisms on the same individual plant (e.g., in marigolds, some fruits are dispersed by animals, while others are dispersed by wind).

The vast diversity of fruit and seed types and their dispersal mechanisms ensures the survival and evolutionary success of the species.