Fruit (plant structure)
Fruits are the mature
In some fruits, the edible portion is not derived from the ovary, but rather from the aril, such as the mangosteen or pomegranate, and the pineapple from which tissues of the flower and stem provide food.
The
.Categories of fruits
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] An example of a pepo is the cucumber and a lemon would be 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 would be 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 in order for their populations to survive.
Evolutionary history
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
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
In fleshy fruits, the pericarp is typically made up of three distinct layers: the epicarp (also known as exocarp), which is the outermost layer; the mesocarp, which is the middle layer; and the endocarp, which is the inner layer surrounding the ovary or the seeds. In a citrus fruit, the epicarp and mesocarp make up the peel. In dry fruits, the layers of the pericarp are not clearly distinguishable.
Epicarp
Epicarp (from
Flavedo
Flavedo is mostly composed of
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
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. 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, as is found in citrus fruit, the mesocarp is also referred to as albedo or pith. It is the inner part of the peel and is commonly removed before eating. In citron fruit, where the mesocarp is the most prominent part, it is used to produce succade.
Endocarp
Endocarp (from Greek: endo-, "inside" + -carp, "fruit") is a
In nuts, it is the stony layer that surrounds the kernel of pecans, walnuts, etc., and that is removed before consumption.
In
Anatomy of grass fruits
The grains of
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.[8]
See also
References
- ^ )
- ^ OCLC 820489734.
- ^ PMID 25009543.
- ^ ISSN 0024-4066.
- PMID 27856652.
- ISBN 978-1-139-48636-1.
- ISBN 978-0-7069-8685-3.
- PMID 29257090.
External links
- Rendle, Alfred Barton (1911). Chisholm, Hugh (ed.). Encyclopædia Britannica. Vol. 11 (11th ed.). Cambridge University Press. pp. 254–260. . In