Fruits are the mature ovaries of flowering plants, protecting seeds and aiding dispersal. They come in three main categories: simple, aggregate, and multiple, each with unique developmental origins and structures. Understanding fruit types helps us grasp their diverse roles in plant reproduction.

Fruit development involves complex changes triggered by fertilization. The process includes seed formation, ovary wall transformation, and sometimes accessory tissue involvement. Hormones like auxins and gibberellins regulate these changes, resulting in the varied fruits we see in nature.

Types of fruits

• Fruits are the mature ovaries of flowering plants that develop from the ovary wall after fertilization
• Fruits play a crucial role in protecting the developing seeds and aiding in their dispersal
• The three main categories of fruits are simple, aggregate, and multiple, which differ in their developmental origin and structure

Simple vs aggregate vs multiple fruits

• Simple fruits (apples, peaches) develop from a single ovary of a single flower and may be either fleshy or dry
• Aggregate fruits (raspberries, blackberries) form from multiple ovaries within a single flower that remain separate but attached to a common receptacle
• Multiple fruits (pineapples, figs) are derived from the ovaries of multiple flowers that are closely packed together and often fused

Fleshy vs dry fruits

• Fleshy fruits have a soft, juicy pericarp at maturity due to the accumulation of water and sugars (berries, drupes)
• Dry fruits have a hard, papery, or leathery pericarp at maturity and are further classified as dehiscent or indehiscent
  • Dehiscent fruits (legumes, capsules) split open at maturity to release the seeds
  • Indehiscent fruits (nuts, achenes) remain closed at maturity, and the entire fruit is dispersed as a unit

Fruit development

• The transformation of an ovary into a fruit involves complex physiological and morphological changes triggered by fertilization
• Fruit development is a coordinated process that includes seed formation, ovary wall transformation, and sometimes the involvement of accessory tissues

Fertilization and seed formation

• Fertilization of the ovule by the pollen tube initiates seed development within the ovary
• The zygote undergoes mitosis to form the embryo, while the triploid endosperm provides nutrition for the developing embryo
• The integuments of the ovule harden to form the protective seed coat

Ovary wall transformation

• After fertilization, the ovary wall undergoes dramatic changes in size, texture, and composition to form the pericarp
• Cell division, cell enlargement, and the accumulation of storage compounds (sugars, starch, oils) contribute to the growth and ripening of the fruit
• Hormonal signals, particularly auxins and gibberellins, play a crucial role in regulating fruit development

Accessory tissue involvement

• In some cases, tissues other than the ovary contribute to the formation of the fruit (strawberries, apples)
• These accessory tissues, such as the receptacle or hypanthium, enlarge and become fleshy, often forming the edible portion of the fruit
• The true fruits, derived from the ovaries, are sometimes embedded within the accessory tissue (achenes in strawberries, core in apples)

Fruit anatomy

• The structure of a fruit reflects its developmental origin and plays a crucial role in its function, particularly in seed protection and dispersal
• Key anatomical features of fruits include the pericarp layers, locules, placentas, and dehiscence mechanisms

Pericarp layers

• The pericarp, derived from the ovary wall, is typically differentiated into three distinct layers: exocarp, mesocarp, and endocarp
• The exocarp is the outermost layer, often forming a protective skin or rind (peels, rinds)
• The mesocarp is the middle layer, which may be fleshy (drupes) or fibrous (coconuts) depending on the fruit type
• The endocarp is the innermost layer, which can be membranous, leathery, or stony (pits in drupes, parchment-like in apples)

Locules and placentas

• Locules are the chambers within the ovary that contain the ovules and developing seeds
• The number and arrangement of locules vary among fruit types and are determined by the number of carpels and their fusion pattern
• Placentas are the regions within the ovary where the ovules are attached, and their position (axile, parietal, free-central) influences fruit structure

Dehiscence mechanisms

• Dehiscence is the opening of a fruit to release its seeds, and the mechanisms of dehiscence are diverse among fruit types
• Septicidal dehiscence occurs when the fruit splits along the septa between the locules (rhododendrons, lilies)
• Loculicidal dehiscence involves the splitting of the fruit along the middle of each locule (irises, tulips)
• Circumscissile dehiscence occurs when a lid-like structure separates from the fruit, releasing the seeds (plantains, purslanes)

Seed dispersal strategies

• Seed dispersal is the movement of seeds away from the parent plant, which reduces competition and increases the chances of successful establishment
• Fruits have evolved various adaptations to facilitate seed dispersal by wind, animals, and water

Wind dispersal adaptations

• Wind-dispersed fruits are typically small, lightweight, and have structures that increase their surface area (wings, plumes)
• Samaras are winged fruits that are easily carried by the wind (maples, ashes)
• Some fruits have feathery or hairy appendages that allow them to be carried aloft (dandelions, cottonwoods)
• Tumbleweeds are plants that break off at the base and are rolled by the wind, scattering seeds as they move

Animal dispersal adaptations

• Animal-dispersed fruits often have bright colors, attractive odors, and nutritious rewards to encourage consumption by animals
• Fleshy fruits are commonly dispersed by birds and mammals that consume the fruit and pass the seeds through their digestive tracts (berries, drupes)
• Some fruits have hooks, barbs, or sticky surfaces that allow them to adhere to animal fur or feathers for transport (burdocks, beggar's ticks)
• Ants disperse seeds with elaiosomes, which are fleshy appendages rich in lipids and proteins (violets, trilliums)

Water dispersal adaptations

• Water-dispersed fruits are typically buoyant and have waterproof coatings or air-filled cavities that allow them to float
• Coconuts have a fibrous husk and a hard, waterproof shell that enables them to drift on ocean currents to new shores
• Some fruits have spongy or corky tissues that provide buoyancy (sedges, rushes)
• Mangrove trees produce viviparous seedlings that are already germinated and can establish quickly when washed ashore

Ecological roles of fruits

• Fruits play crucial ecological roles in protecting and nourishing seeds, attracting dispersal agents, and regulating germination
• These roles are essential for the successful reproduction and survival of plant species in various ecosystems

Seed protection and nourishment

• Fruits provide a protective covering for the developing seeds, shielding them from physical damage, desiccation, and predation
• The pericarp can be tough, spiny, or chemically defended to deter herbivores and pathogens (nuts, capsules)
• Fruits also supply nutrients to the developing seeds, particularly through the endosperm or perisperm tissues (grains, legumes)

Dispersal agent attraction

• Fruits have evolved various traits to attract specific dispersal agents, such as birds, mammals, and insects
• Fleshy fruits often have bright colors (berries), strong odors (durians), and sugary or fatty rewards (avocados) to encourage consumption by animals
• Some fruits mimic the appearance or scent of flowers (figs) or carrion (stapeliads) to attract specialized pollinators or dispersers

Germination regulation

• Fruits can regulate seed germination by imposing physical or chemical dormancy, which prevents premature germination
• Hard seed coats or thick pericarps can mechanically restrict germination until conditions are favorable (stone fruits, nuts)
• Some fruits contain germination inhibitors that must be leached out or degraded before seeds can germinate (tomatoes, cucumbers)
• Scarification, cold stratification, or passage through an animal's digestive tract may be required to break dormancy and initiate germination

Economic importance of fruits

• Fruits have immense economic value as food sources, industrial and medicinal raw materials, and ornamental or aesthetic products
• The cultivation, processing, and trade of fruits contribute significantly to global agriculture and the economy

Edible fruits as food sources

• Many fruits are consumed fresh or processed into various food products, providing essential nutrients, flavors, and culinary diversity
• Major fruit crops include apples, bananas, citrus fruits, grapes, and berries, which are traded globally and support local economies
• Fruit-derived products, such as jams, jellies, juices, and dried fruits, are also economically important

Industrial and medicinal uses

• Fruits serve as raw materials for various industrial applications, including the production of dyes, fibers, and biofuels
• Cotton and kapok fruits provide natural fibers for the textile industry
• Some fruits contain compounds with medicinal properties, such as the anti-cancer drug paclitaxel from yew trees
• Essential oils, flavors, and fragrances extracted from fruits (citrus peels, vanilla beans) are used in the cosmetic and food industries

Ornamental and aesthetic value

• Many fruits are valued for their ornamental qualities, such as attractive colors, unusual shapes, or decorative structures
• Ornamental fruits, like Chinese lanterns and bittersweet vines, are used in floral arrangements and crafts
• Fruit trees and shrubs are popular in landscaping and home gardens for their aesthetic appeal and seasonal interest
• Some fruits, like gourds and pumpkins, are used for decorative purposes or in cultural traditions and festivals