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Fruit (plant structure)
Fruit (plant structure)
Fruit (plant structure)
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Longitudinal section of a female flower of a squash plant (courgette), showing the ovary (with ovules), style and stigmas

Fruits are the mature ovary or ovaries of one or more flowers. They are found in three main anatomical categories: aggregate fruits, multiple fruits, and simple fruits.

Fruitlike structures may develop directly from the seed itself rather than the ovary, such as a fleshy aril or sarcotesta.

The grains of grasses are single-seed simple fruits wherein the pericarp and seed coat are fused into one layer. This type of fruit is called a caryopsis. Examples include cereal grains, such as wheat, barley, oats and rice.

Categories of fruits

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Fruits are found in three main anatomical categories: aggregate fruits, multiple fruits, and simple fruits. Aggregate fruits are formed from a single compound flower and contain many ovaries or fruitlets.[1] Examples include raspberries and blackberries. Multiple fruits are formed from the fused ovaries of multiple flowers or inflorescence.[1] An example of multiple fruits are the fig, mulberry, and the pineapple.[1] Simple fruits are formed from a single ovary and may contain one or many seeds. They can be either fleshy or dry. In fleshy fruit, during development, the pericarp and other accessory structures become the fleshy portion of the fruit.[2] The types of fleshy fruits are berries, pomes, and drupes.[3] In berries, the entire pericarp is fleshy but this excludes the exocarp which acts as more as a skin. There are berries that are known as pepo, a type of berry with an inseparable rind, or hesperidium, which has a separable rind.[2] A cucumber is an example of a pepo, while a lemon is an example of a hesperidium. The fleshy portion of the pomes is developed from the floral tube and like the berry most of the pericarp is fleshy but the endocarp is cartilaginous; an apple is an example of a pome.[2] Lastly, drupes are known for being one-seeded with a fleshy mesocarp; an example of this is the peach.[2] However, there are fruits where the fleshy portion is developed from tissues that are not the ovary, such as in the strawberry. The edible part of the strawberry is formed from the receptacle of the flower. Due to this difference the strawberry is known as a false fruit or an accessory fruit.

There is a shared method of seed dispersal within fleshy fruits. These fruits depend on animals to eat the fruits and disperse the seeds (endozoochory) in order for their populations to survive.[3] Dry fruits also develop from the ovary, but unlike the fleshy fruits they do not depend on the mesocarp but the endocarp for seed dispersal.[3] Dry fruits depend more on physical forces, like wind and water. Dry fruits' seeds can also perform pod shattering, which involve the seed being ejected from the seed coat by shattering it. Some dry fruits are able to perform seed pod explosions, such as wisteria, resulting the seed to be dispersed over long distances. Like fleshy fruits, dry fruits can also depend on animals to spread their seeds by adhering to animal's fur and skin, this is known as epizoochory. Types of dry fruits include achenes, capsules, follicles or nuts. Dry fruits can also be separated into dehiscent and indehiscent fruits. Dry dehiscent fruits are described as a fruit where the pod has an increase in internal tension to allow seeds to be released. These include the sweet pea, soybean, alfalfa, milkweed, mustard, cabbage and poppy.[3] Dry indehiscent fruit differ in that they do not have this mechanism and simply depend on physical forces. Examples of species indehiscent fruit are sunflower seeds, nuts, and dandelions.[3]

Evolutionary history

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There is a wide variety in the structures of fruit across the different species of plants. Evolution has selected for certain traits in plants that would increase their fitness. This diversity arose through the selection of advantageous methods for seed protection and dispersal in different environments.[3] It is known that dry fruits were present before fleshy fruits and fleshy fruits diverged from them.[3] A study looking at the family Rubiaceae found that within the family, fleshy fruits had evolved independently at least 12 times.[4] This means that fleshy fruits were not passed on to following generations but that this form of fruit was selected for in different species. This may imply that fleshy fruit is a favorable and beneficial trait because not only does it disperse the seeds, but it also protects them.[5] There is also a variety of dispersal methods that are used by different plants. The origins of these modes of dispersal have been found to be a more recent evolutionary change.[4] Of the methods of dispersal, the plants that use animals have not changed in many ways from the original trait. Due to this, it may be assumed that animal dispersal is an efficient form of dispersal, however there has been no evidence that it increases dispersal distances.[4] Therefore, the question remains of what evolutionary mechanism causes such dramatic diversity. It has been found, however, that simple changes within developmental regulatory genes can cause large alterations within the anatomical structure of the fruit.[3] Even without knowing the mechanism involved in the biodiversity of fruit, it is clear that this diversity is important to the continuation of plant populations.

Anatomy of simple fruits

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Diagram of a typical drupe (in this case, a peach), showing both fruit and seed
A schematic picture of an orange hesperidium
A segment of an orange that has been opened to show the pulp (juice vesicles) of the endocarp

Fruit anatomy is the plant anatomy of the internal structure of fruit.[6][7] In berries and drupes, the pericarp forms the edible tissue around the seeds. In other fruits such as citrus and stone fruits (Prunus) only some layers of the pericarp are eaten. In accessory fruits, other tissues develop into the edible portion of the fruit instead, for example the receptacle of the flower in strawberries.

Pericarp layers

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In fleshy fruits, the pericarp is typically made up of three distinct layers: the outer epicarp, the middle mesocarp and the inner endocarp. These layers vary in thickness and texture, and may blend into each other. In a hesperidium like lemon, the epicarp and mesocarp make up the peel; in many berries like melons or cucumbers (pepo), the mesocarp and endocarp make up the flesh.[8]

In dry fruits, the layers of the pericarp are usually hard, dry and not clearly distinguishable.

Epicarp

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Coconut's husk
Husk of a coconut (smooth exocarp plus fibrous mesocarp)

Epicarp (from Greek: epi-, "on" or "upon" + -carp, "fruit") is a botanical term for the outermost layer of the pericarp (or fruit).[8] The epicarp forms the tough outer skin of the fruit, if there is one. The epicarp is sometimes called the exocarp, or, especially in citrus, the flavedo (zest).

Flavedo

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Flavedo is mostly composed of cellulosic material but also contains other components, such as essential oils,[9] pigments (carotenoids, chlorophylls, flavonoids),[10] paraffin waxes, steroids and triterpenoids, fatty acids, bitter principles (limonin), and enzymes.

In citrus fruits, the flavedo constitutes the peripheral surface of the pericarp. It is composed of several cell layers that become progressively thicker in the internal part; the epidermic layer is covered with wax and contains few stomata, which in many cases are closed when the fruit is ripe.

When ripe, the flavedo cells contain carotenoids (mostly xanthophyll) inside chromoplasts, which, in a previous developmental stage, contained chlorophyll. This hormonally controlled progression in development is responsible for the fruit's change of color from green to yellow upon ripening. Citrus flavedo may be scraped off the fruit to create zest.

The internal region of the flavedo is rich in multicellular bodies with spherical or pyriform shapes, which are full of essential oils.

Mesocarp

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The mesocarp (from Greek: meso-, "middle" + -carp, "fruit") is the fleshy middle layer of the pericarp of a fruit; it is found between the epicarp and the endocarp.[8] It is usually the part of the fruit that is eaten. For example, the mesocarp makes up most of the edible part of a peach, and a considerable part of a tomato. "Mesocarp" may also refer to any fruit that is fleshy throughout.

In a hesperidium, the mesocarp is the inner part of the peel and is commonly removed before eating, as is found in citrus fruit.[8] It is also referred to as albedo or pith. In citron fruit, where the mesocarp is the most prominent part, it is used to produce succade.

Endocarp

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Almond endocarp

Endocarp (from Greek: endo-, "inside" + -carp, "fruit") is a botanical term for the inside layer of the pericarp (or fruit), which directly surrounds the seeds. It may be membranous as in citrus where it is the only part consumed, or thick and hard as in the pyrenas of drupe fruits of the family Rosaceae such as peaches, cherries, plums, and apricots.

In nuts, it is the stony layer that surrounds the kernel of pecans, walnuts, etc., and that is removed before consumption.

In citrus fruits, the endocarp is separated into sections, which are called segments. These segments are filled with juice vesicles, which contain the juice of the fruit.

Anatomy of grass fruits

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The grains of grasses are single-seed simple fruits wherein the pericarp (ovary wall) and seed coat are fused into one layer. This type of fruit is called a caryopsis. Examples include cereal grains, such as wheat, barley, and rice.

The dead pericarp of dry fruits represents an elaborated layer that is capable of storing active proteins and other substances for increasing survival rate of germinating seeds.[11]

See also

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References

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Revisions and contributorsEdit on WikipediaRead on Wikipedia

Fruit (plant structure)

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from Grokipedia
In , a is defined as the mature, ripened of a (angiosperm), along with its contents, which typically includes one or more developed from fertilized ovules. This structure arises from the flower's pistil after and fertilization, though some fruits form parthenocarpically without fertilization. Unlike the common culinary sense of fruits as sweet, edible plant parts, the botanical definition encompasses a wide range of structures, including those typically classified as , such as tomatoes and cucumbers. The primary structure of a fruit consists of the pericarp, the wall of the ripened , which develops into three distinct layers: the outer exocarp (or ), the middle mesocarp (fleshy or fibrous tissue), and the inner endocarp (often hardened around seeds). Seeds within the fruit are attached to the via a funiculus and are housed in locules, compartments formed by the ovary walls. Fruits may also incorporate accessory tissues from other floral parts, such as the receptacle, leading to structures like pomes (e.g., apples) where the core is the true fruit and the surrounding flesh is accessory. Fruits are classified based on their origin, texture, and dehiscence (whether they split open to release seeds). Simple fruits develop from a single or carpel, as in berries (e.g., grapes) or drupes (e.g., peaches with a stony endocarp). Aggregate fruits form from multiple carpels of one flower, such as raspberries composed of drupelets, while multiple fruits arise from the ovaries of many flowers clustered together, like pineapples. Fleshy fruits, with a succulent pericarp, include types like hesperidia ( fruits with leathery rinds) and pepos (e.g., pumpkins with hard outer rinds but pulpy interiors), whereas dry fruits are either dehiscent (e.g., like peas that split along seams) or indehiscent (e.g., achenes like sunflowers that remain closed). The fundamental functions of fruits are to protect developing seeds from environmental stresses and to facilitate , enabling the plant's in new locations. Dispersal mechanisms vary: fleshy fruits attract animals for consumption and seed passage through , while dry fruits may rely on , , or explosive dehiscence. This evolutionary adaptation underscores fruits' role in angiosperm diversity and ecological interactions.

Overview and Definition

Botanical Definition

In , a is the mature, ripened of a , an angiosperm, that usually develops after and fertilization (though some form parthenocarpically without fertilization) and typically encloses one or more . This structure forms as the ovules within the ovary may mature into seeds, while the ovary wall undergoes transformation to protect and aid in the dissemination of those seeds. Parthenocarpic fruits, such as some bananas and navel oranges, develop without fertilization, resulting in seedless structures that still qualify as fruits botanically. The fruit's wall, termed the pericarp, derives directly from the ovary wall and may consist of one to three distinct layers—the exocarp (outer skin), mesocarp (middle layer), and endocarp (inner layer)—depending on the species, which can be fleshy, dry, or fibrous to suit various ecological needs. Seeds within the fruit represent the fertilized ovules, ensuring the of the plant by providing nourishment and protection during early development. This precise definition distinguishes fruits from other plant organs, such as leaves or stems, emphasizing their origin in the flower's . Unlike angiosperms, gymnosperms do not produce true , as their remain exposed or "naked" on scales or similar structures without enclosure by an ovary-derived pericarp, highlighting a key evolutionary divergence in reproduction. The botanical concept of applies solely to angiosperms, excluding structures like cones, which serve analogous but distinct functions. The term "fruit" originates from the Latin fructus, meaning "enjoyment," "use," or "produce," originally referring to agricultural yields valued for human consumption. Its application in scientific was formalized in the 18th century by , who in works like Philosophia Botanica (1751) integrated the term into systematic classification, defining fruits based on their derivation from the to describe plant reproductive diversity.

Role in Reproduction and Dispersal

Fruits play a crucial role in angiosperm reproduction by enclosing and protecting developing s within the pericarp, the fruit wall derived from the , which shields them from , predation, and environmental stresses such as extreme temperatures or mechanical damage. The pericarp's layered structure often includes waterproofing agents like or waxes to prevent moisture loss, while lignified tissues provide mechanical barriers against herbivores and pathogens, thereby enhancing seed viability during maturation. For instance, in coconuts (Cocos nucifera), the fibrous pericarp maintains seed hydration in arid conditions, allowing long-term . Beyond protection, fruits facilitate , ensuring propagation away from the parent plant to reduce and increase potential. Animal-mediated dispersal, or zoochory, involves fleshy fruits that attract vertebrates like s and mammals through nutritious pulp, with seeds passing unharmed through the digestive tract to be deposited at distant sites. Berries, such as those of blueberries ( spp.), are adapted for dispersal, where their bright colors and soft texture promote consumption and subsequent excretion. In contrast, dispersal (anemochory) relies on lightweight, dry fruits with structures like wings or plumes to aid airborne transport; samaras of maples (Acer spp.) exemplify this, with their autorotating wings enabling seeds to glide far from the source. Water dispersal (hydrochory) features buoyant fruits that float on rivers or oceans, as seen in mangroves ( spp.), where air-filled tissues prevent sinking while the pericarp resists water ingress. Ballistic dispersal involves explosive dehiscence of dry fruits, propelling seeds short distances via tension-built structures, such as in touch-me-nots ( spp.), where pod drying triggers sudden splitting. This dual function of protection and dispersal confers a significant evolutionary advantage to angiosperms over gymnosperms, whose naked seeds lack such enclosures and are more vulnerable to predation and , resulting in lower survival rates. Fruits enable targeted dissemination, often via mutualistic interactions with animals, which boosts success and compared to the wind-reliant, exposed seeds of gymnosperms. Consequently, this innovation has contributed to the dominance of angiosperms, with studies indicating up to 90% of tropical woody benefiting from animal-dispersed fruits for enhanced fitness.

Evolutionary History

Origins in Angiosperms

The origins of fruits represent a defining in the of angiosperms, emerging during the period around 140–130 million years ago, a time that marked the initial of flowering from their ancestors. In contrast to gymnosperms, whose remain exposed and unprotected on scales, angiosperm ovules are fully enclosed within ovaries of the carpel, which mature into fruits after fertilization, offering enhanced protection against desiccation and herbivores while promoting targeted . This structural advancement, tied to the of closed carpels, allowed for greater reproductive and adaptability in diverse environments. Key fossil evidence illuminating these early fruits comes from the in Province, , where specimens of Archaefructus sinensis, dated to approximately 125 million years ago, preserve herbaceous shoots with simple fruit-like structures. These consist of paired follicles—elongated, dehiscent fruits that split open to release multiple seeds—attached to an elongated axis, demonstrating rudimentary yet functional fruit morphology in one of the basalmost known angiosperms. Archaefructus likely inhabited shallow aquatic or semi-aquatic habitats, highlighting the initial experimentation with enclosed reproductive units that foreshadowed the diversity of fruits to come. This fruit innovation was instrumental in the ascendancy of angiosperms, facilitating efficient that outpaced the wind-reliant strategies of gymnosperms and enabling rapid of new habitats. By providing nutritious, often fleshy rewards for vectors, early fruits fostered coevolutionary relationships that amplified angiosperm diversification, ultimately leading to their ecological dominance by the , when they comprised over 80% of plant species in many floras.

Adaptations Over Time

Over the course of angiosperm , dry fruits emerged as the ancestral form, primarily adapted for abiotic dispersal mechanisms such as or , while fleshy fruits arose independently approximately 100 times, often transitioning from dehiscent dry structures like capsules to indehiscent fleshy types like berries to facilitate animal-mediated dispersal. This shift was driven by the development of attractive traits in fleshy fruits, including vibrant colors produced by pigments such as anthocyanins, which reflect light in the red spectrum (600–700 nm) to appeal to dispersers, and scents that signal to mammals, enhancing detection and consumption rates. For instance, anthocyanin accumulation in fruits like those of species not only serves as a visual cue but also provides photoprotection against UV , allowing to thrive in diverse light environments. In parallel, dehiscence mechanisms in dry fruits evolved convergently multiple times across angiosperm lineages, featuring specialized sutures where the pericarp splits open upon maturation to release through built-up internal tension. These sutures, often reinforced by lignified tissues in the endocarp, enable explosive or gradual opening, as seen in pods, promoting efficient seed scattering in habitats where animal vectors are scarce. Such adaptations underscore the selective pressure for precise timing in seed liberation to avoid predation while maximizing dispersal distance. Co-evolutionary dynamics with dispersers further refined fruit structures, with hooks or barbs developing on dry fruits like those of burdock () to attach externally to for exozoochory, a strategy that proliferated in open habitats during the . Simultaneously, many fruits incorporated toxins, such as cyanogenic glycosides or alkaloids in the pulp, to deter by causing aversion in non-dispersing herbivores while tolerating passage through mutualistic frugivores' digestive systems. This protects developing seeds from overconsumption, as evidenced in species like where immature fruits exhibit higher toxicity to pathogens and predators. By the Miocene epoch (23–5.3 million years ago), fruit diversification accelerated amid climate shifts toward aridity and the rise of open savannas, transitioning from simple single-ovary structures to complex aggregates and multiples in families like , where larger pomes and drupes evolved via hybridization to exploit megafaunal dispersers. records from this period, including enlarged endocarps in , illustrate how these innovations enabled colonization of new ecosystems, with aggregate forms like raspberries enhancing seed packaging for efficient long-distance transport.

Fruit Development

From Ovary to Mature Fruit

Following successful pollination and double fertilization in angiosperms, one sperm nucleus fuses with the egg cell to form the diploid zygote, which develops into the embryo, while the second sperm nucleus fuses with the central cell to produce the triploid endosperm, providing nourishment for the embryo. The ovules within the ovary enlarge as they mature into seeds, and the ovary wall begins to expand dramatically, differentiating into the pericarp that forms the protective fruit tissue enclosing the seeds. This post-fertilization expansion is driven by the influx of nutrients and water, initiating the transformation from a floral structure to a mature fruit. Fruit development proceeds through distinct morphological and cellular stages, beginning with fruit set shortly after fertilization, where the ovary transitions from a static to a growing state. The initial phase features rapid cell division and proliferation in the ovary tissues, particularly in the pericarp, lasting typically 1-4 weeks and determining the final number of cells that influence fruit size. This is followed by a phase of cell enlargement, where existing cells expand in volume through water uptake and vacuolar growth, contributing to overall fruit swelling. During maturation, the fruit undergoes structural changes such as lignification in dry fruits for dehiscence or softening in fleshy fruits via cell wall modification, culminating in ripeness when seeds are viable and the fruit is dispersal-ready. In some cases, fruit formation occurs without fertilization through , where the develops into a due to genetic or environmental triggers, bypassing the need for . A prominent example is the cultivated (), in which ovules degenerate and the pericarp expands into pulp-filled tissue without seed formation. The timing of these developmental stages varies widely by species; for instance, apple (Malus domestica) fruit maturation from fertilization to harvest generally spans 3-6 months, encompassing in the first few weeks post-petal fall and subsequent expansion over the .

Hormonal and Genetic Controls

The development of fruit is tightly regulated by plant hormones that coordinate cell expansion, growth, and maturation processes. Auxins and gibberellins play pivotal roles in promoting fruit set and early growth by stimulating cell expansion and division. Auxins, such as indole-3-acetic acid, facilitate parthenocarpic fruit development and delay ripening by antagonizing ethylene action, as demonstrated in tomato where auxin response factors like SlARF2 are essential for coordinating these responses. Gibberellins similarly enhance fruit elongation and interact synergistically with auxins to support ovary growth post-pollination. Ethylene, a gaseous hormone, is central to ripening, particularly in climacteric fruits like tomato and banana, where it triggers autocatalytic biosynthesis leading to rapid maturation, softening, and color changes; in contrast, non-climacteric fruits such as strawberry and grape rely on alternative cues for gradual ripening without this burst. Genetic mechanisms underpin these hormonal actions through transcription factors that dictate ovary identity and tissue differentiation. MADS-box genes, a family of regulatory proteins, are key orchestrators; for instance, the FRUITFULL (FUL) gene in specifies pericarp identity and prevents premature dehiscence by repressing SHATTERPROOF genes, ensuring proper fruit wall development. In , the MADS-RIN gene integrates ethylene signaling to activate ripening genes like ACS2 and ACS4, linking hormonal and genetic pathways during maturation. These genes form complexes that fine-tune pericarp differentiation, with mutations often resulting in aberrant fruit morphology. Environmental factors modulate hormone synthesis and efficacy, influencing fruit development trajectories. Light quality and intensity regulate and production. Temperature extremes alter hormone balances; low temperatures enhance accumulation in pistils to prevent , while high temperatures boost (ABA) levels, promoting dormancy in seeds and delaying ripening in species such as . ABA primarily induces by inhibiting under stress, as seen in its role during late embryogenesis to maintain viability. Cytokinins, meanwhile, drive seed development by sustaining growth and nutrient partitioning, with elevated levels in seeds correlating with rapid early fruit expansion. These interactions ensure adaptive responses to external cues during fruit maturation. Recent advances as of 2025 have further elucidated hormonal networks, including ' interplay with and in regulating traits like softening and flavor in various fruits. signaling has been shown to mediate parthenocarpic development through integrated hormonal pathways. Additionally, CRISPR/Cas has enabled targeted modifications in fruit crops, enhancing traits like size and stress resistance by altering key genetic regulators.

Classification of Fruits

Simple Fruits

Simple fruits develop from the of a single flower, which may consist of one carpel or multiple fused carpels, resulting in a structure where the pericarp forms the fruit wall surrounding the . This contrasts with more complex fruit types by originating from a single pistil unit, emphasizing the fruit's role in enclosing and protecting derived solely from one flower's reproductive organ. Simple fruits are broadly classified into fleshy and dry subtypes based on the pericarp's texture at maturity. Fleshy simple fruits have a soft, moist pericarp that aids in animal-mediated , including , drupes, and pomes. A features a fleshy pericarp throughout with multiple seeds embedded, as seen in the (Solanum lycopersicum), where the entire fruit wall is edible and juicy; include subtypes like hesperidia ( fruits with leathery exocarp) and pepos (e.g., cucumbers with hard exocarp but fleshy interior). Drupes possess a thin outer skin (exocarp), fleshy middle layer (mesocarp), and hard inner stone (endocarp) enclosing one or few seeds, exemplified by the (Prunus persica), where the pit protects the seed. Pomes, such as the apple (Malus domestica), are simple fruits with a central core from the ovary but fleshy tissue primarily from the (receptacle), briefly noting their accessory nature while the core remains the true fruit. Dry simple fruits, in contrast, have a hardened pericarp and are further divided into dehiscent and indehiscent forms depending on whether they split open to release seeds. Dehiscent dry fruits open along specific lines at maturity to disperse seeds, with the being a key example: a single carpel that splits along two sutures, as in the pea pod (Pisum sativum), releasing multiple seeds. Indehiscent dry fruits remain closed, retaining seeds within the pericarp until external forces intervene, such as the , a small single-seeded fruit where the pericarp is thin and loosely attached to the seed, like the (Helianthus annuus). This classification highlights how simple fruits adapt dispersal strategies through pericarp properties without accessory floral parts dominating the structure.

Compound Fruits

Compound fruits, also known as composite fruits, develop from multiple or incorporate tissues beyond the , resulting in a structure composed of several individual fruits or fruit-like units fused together. Unlike simple fruits, which arise from a single , compound fruits exhibit greater complexity in their formation and often enhance through collective structures. These fruits are categorized into aggregate, multiple, and accessory types based on their developmental origins. Aggregate fruits form from a single flower that possesses multiple carpels, each developing into a small, independent fruitlet clustered on a common receptacle. In this type, the individual fruitlets—such as drupelets in raspberries (Rubus idaeus)—remain distinct but are fused at their bases, creating a cohesive unit that aids in animal-mediated dispersal. For instance, the raspberry consists of numerous tiny drupes arising from separate ovaries within one flower, with the fleshy receptacles providing edibility. Multiple fruits, sometimes called collective fruits, originate from an entire where the ovaries of numerous closely packed flowers develop and merge into a single mass, often incorporating the inflorescence axis. This fusion results in a complex structure where individual fruits from different flowers coalesce, as seen in the (Ananas comosus), composed of up to 200 berries embedded in a fleshy axis derived from the inflorescence. Similarly, the (Ficus carica) forms a syconus, a specialized multiple fruit where numerous tiny drupelets line an inverted receptacle from multiple florets. Accessory fruits are a variant often overlapping with aggregate types, where significant portions of the fruit derive from tissues outside the , such as an enlarged receptacle or floral parts, while true fruitlets form from the ovaries. The strawberry ( × ananassa) exemplifies this, with its edible swollen receptacle bearing surface achenes (small dry fruits) from multiple ovaries, making the fleshy part non-ovarian in origin. This accessory development enhances attractiveness to dispersers without altering the pericarp-based identity of the embedded fruitlets. Structural variations in fruits commonly involve the fusion of multiple pericarps into a unified outer layer, which can be fleshy, dry, or a combination, promoting efficient protection and dispersal of embedded seeds. In aggregate and multiple forms, this per carp fusion creates a seamless envelope, as in the (), where drupelets' exocarps merge while retaining internal distinctions. Such integrations optimize the fruit's role in by balancing structural integrity with accessibility.

Anatomy of Fruits

General Structural Components

The fruit, as a mature in angiosperms, primarily comprises two core components: the pericarp and the seeds. The pericarp develops from the wall of the and encloses the seeds, providing protection and often aiding in dispersal. In some cases, additional floral structures such as the receptacle or floral tube may fuse with or contribute to the fruit's outer layers, expanding its structure beyond the alone. Seeds within the fruit typically consist of the , often with , and the testa. In some cases, the endosperm is absent in mature seeds as it has been absorbed by the cotyledons. The is the young , featuring a for root development, an epicotyl for shoot growth, and one or two cotyledons that store or absorb nutrients. The serves as a nutritive tissue, derived from , supplying essential reserves like and proteins to the developing . The testa, or seed coat, forms from the ovule's integuments, offering mechanical protection and sometimes regulating through impermeability or mechanisms. Fruits maintain vascular connections that facilitate nutrient supply during development and maturation. These include extensions from the peduncle, the stalk attaching the fruit to the , which conducts water, minerals, and sugars via and bundles. Remnants of the style, the elongated portion of the pistil, may also persist, providing additional vascular pathways for to the seeds. Fruits exhibit wide variations in size and shape, influencing dispersal strategies and ecological roles. Examples range from tiny capsules in tobacco (Nicotiana tabacum), measuring about 1-2 cm and containing numerous minute seeds, to massive drupes in coconut (Cocos nucifera), reaching 15-30 cm in length with a fibrous husk. Shapes can be spherical, as in many berries, or elongated, like pods in legumes, adapting to wind, animal, or ballistic dispersal. At the seed-fruit interface, the funicle anchors the seed to the placental tissue within the pericarp, leaving a scar called the hilum upon maturation. This connection ensures nutrient transfer during seed development. Accessory structures such as the aril, a fleshy outgrowth from the funicle, or the caruncle, a similar protuberance near the micropyle, may develop in some species, enhancing attractiveness to dispersers by providing lipid-rich rewards.

Pericarp Layers

The pericarp, derived from the differentiation of the ovary wall during fruit maturation, typically exhibits a tripartite structure in most angiosperm fruits, consisting of the outer exocarp, middle mesocarp, and inner endocarp. This layered organization arises from distinct histogenetic zones of the carpel: the exocarp from the outer , the mesocarp from the mesophyll, and the endocarp from the inner locular . Each layer contributes to the fruit's overall protective, nutritional, and dispersal functions, with involving for storage, sclerenchyma for mechanical support, and collenchyma for flexibility in certain cases. The exocarp, also known as the epicarp, forms the outermost layer and serves primarily as a protective barrier against environmental stresses such as pathogens, , and mechanical damage. It typically consists of a single layer of specialized epidermal cells, often covered by a , and may include additional features like hairs or glands; for instance, in citrus fruits, the exocarp encompasses the flavedo, the pigmented outer region rich in oil glands. Compositionally, it can incorporate sclerenchyma for added toughness or remain thin and waxy in fleshy fruits. The mesocarp occupies the middle region and often functions as a storage tissue for water, sugars, and nutrients, enhancing and aiding animal-mediated in fleshy fruits. It is usually composed of multiple layers of cells, which can be fleshy and juicy—as in peaches, where it forms the bulk of the edible portion—or fibrous and supportive, as in coconuts. In some species, sclerenchyma develops within the mesocarp to provide structural reinforcement, particularly in dry or protective fruits. The endocarp, adjacent to the seed, primarily ensures seed containment and protection, with its properties varying widely to suit dispersal strategies. It often features sclerenchymatous or lignified cells for hardness in drupes, forming a stony layer around the seed (e.g., the pit in peaches), while remaining soft and parenchymatous in berries like tomatoes. In dehiscent fruits, the endocarp may facilitate splitting for seed release through specialized cell expansion or lignification patterns. Variations in pericarp layering occur across fruit types, including the absence of distinct layers in some dry fruits like achenes, where the pericarp is thin and papery, or fusion of layers in inferior ovaries. Cellular makeup generally relies on for metabolic activity in fleshy regions, sclerenchyma for rigidity in protective zones, and occasional collenchyma for tensile strength, with these tissues differentiating post-fertilization under hormonal and genetic influences.

Specialized Fruit Structures

Grass Fruits (Caryopses)

The represents a specialized dry, indehiscent fruit unique to the family, where the thin pericarp fuses inseparably with the coat (testa), creating a unified structure that functions as both fruit and . This fusion occurs during maturation, with the pericarp's exocarp, mesocarp, and endocarp layers adhering tightly to the testa, often through degeneration and biochemical integration, as seen in (Triticum aestivum) and (). Unlike standard fruits with distinct pericarp and seed separation, this adaptation ensures the protective outer layers remain intact with the internal seed components. Internally, the is dominated by a large that serves as the primary storage reserve for , proteins, and other , comprising up to 90% of the grain's weight in species like . The 's outermost region forms the aleurone layer, a one- to several-cell-thick tissue specialized for mobilization during , containing high levels of , minerals, and hydrolytic enzymes. This layer surrounds the central starchy and the laterally positioned , which includes a prominent scutellum for absorption, while the fused pericarp provides a minimal but durable barrier against environmental stresses. The evolved as a synapomorphy in , marking the culmination of a transformation series toward reduced gynoecial complexity and indehiscence from ancestral structures, enhancing survival through compact, protected units suited for passive dispersal. This form supports wind or gravity-mediated dispersal, as the lightweight, fused design allows efficient release from spikelets without specialized appendages in many grasses. The pericarp-seed coat fusion imparts structural resilience to caryopses, underpinning their economic significance as staple cereals by facilitating mechanical harvesting, storage, and processing without loss of protective or nutritive integrity. In crops like maize (Zea mays) and barley (Hordeum vulgare), this prevents separation during handling, preserving viability and nutritional value for global food systems.

Dehiscent and Indehiscent Variants

Dehiscent fruits are dry fruits that split open along predefined lines of weakness, known as sutures, to facilitate at maturity. This splitting is driven by structural adaptations in the pericarp, including the formation of valves, , or hinges, which allow controlled release of seeds. The mechanism often involves lignified cells in the endocarp and mesocarp layers that provide rigidity and build internal tension as the fruit dries, causing the pericarp to rupture explosively or gradually. Hygroscopic tissues in the pod walls further contribute by contracting differentially upon dehydration, enhancing the force of dehiscence. A classic example of a dehiscent fruit is the follicle, as seen in milkweed (Asclepias species), where the pericarp splits along a single ventral suture upon maturation, releasing plumed seeds for wind dispersal. This process relies on lignification of the endocarp layers to generate the necessary tension for opening. Capsules represent another dehiscent type, often multiseeded and derived from compound ovaries, which dehisce in various patterns such as loculicidal (along the back of the locules) or poricidal (through pores at the top). In poppies (Papaver species), poricidal capsules feature lignified ridges and separation layers that enable explosive valve detachment, scattering tiny seeds when disturbed by wind. Legume pods, such as those in wild beans (Phaseolus), exemplify explosive dehiscence, where non-lignified dehiscence zones along the sutures weaken under tension from lignified bundle sheath fibers, propelling seeds up to several meters. In contrast, indehiscent fruits remain closed at maturity, retaining seeds within the intact pericarp and relying on external agents for dispersal, such as animals or environmental decay. Structural features include a thin, fused pericarp in some types or a hard, woody shell in others, which protects the without allowing active splitting. Achenes are single-seeded indehiscent fruits from a simple , where the pericarp adheres tightly to the seed coat at one point but remains separable overall, often with adaptations like pappus structures for wind dispersal, as in sunflowers (Helianthus annuus). Nuts, another indehiscent variant, feature a hard, lignified exocarp derived from a multicarpellate with only one developing, providing robust protection; examples include acorns (Quercus ), which are dispersed by animals that cache them. These variants highlight the diversity within dry fruit classification, balancing seed protection and dispersal strategies.

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