A pericarp is a fraction of the fruit that constitutes the outer layer in the fruit anatomy, which encloses the seed. It develops from the flower’s ovary and surrounds the seed that develops from an ovule, as a result of plant fertilization. Pericarp can be squishy or sapless. It is the edible tissue of fruit that is differentiated into several distinct layers, namely exocarp, mesocarp, and endocarp.
In some fruits, it is quite difficult to discern each layer of these cells, as the anatomy of fruits differs by varying species. Pericarp in fruit not only guards the seed during its developmental stages but also helps in seed dispersal. Several ways accomplish seed dispersal, including wind, water, birds, or animal transmission that we will discuss further in this article.
Definition of Pericarp
Pericarp can define as the fruit wall that develops out of ovary after the process of fertilization, and differentiates into an endocarp (innermost layer), a mesocarp (intermediate layer), and an exocarp (outermost layer). Sometimes, we get confused between the term pericarp and fruit, but both are different. The pericarp is either a dry or fleshy portion of the fruit, while fruit wholly comprises of a pericarp (develops from an ovary wall) and a seed (develop from an ovule).
It possesses three distinct layers:
- Epicarp: It is the outermost layer that forms the skin or peel of the fruit.
- Mesocarp: It is generally fleshy or dry mid portion of the fruit.
- Endocarp: It is the inmost part surrounding the seed.
In some fruits, all these layers are sometimes difficult to discern, as only a few rows of cells are found. For instance, in fleshy fruits like orange both epicarp and mesocarp compose the peel portion, while the layers of the pericarp are not distinctly identifiable in dry fruits.
Epicarp (epi-“on” + carp-“fruit”) accounts for an outmost covering of the pericarp, which also called as exocarp. It can define as the differentiated, thin, and tough outermost layer of tissue that constitutes the fruit rind or peel. In citrus fruits, this particular portion is termed as the flavedo.
Mesocarp (meso-“middle” + carp-“fruit”) accounts for a layer intermediary to the layer of epicarp and the endocarp, and also called as hypodermis. It can define as the differentiated, fleshy or dry middle layer of tissue that generally constitutes the edible portion of fruit. For instance, the majority of fruits like peach, tomato, etc. the mesocarp makes up most of the edible part.
In citrus fruits (Orange, citrus lemon etc.), the layer of the mesocarp is specifically termed as albedo or pith, which is generally separated prior eating. The inner rind or mesocarp of citrus species is processed to make succade.
Endocarp (endo-“inside” + carp-“fruit”) accounts for an innermost covering of the pericarp, which straightaway encloses the seed. In citrus fruits, the endocarp is the only part consumed that is fractioned into some sections called segments. The juice vesicles are tightly incorporated within these segments containing the fruit juices. On contrary, the stone fruits like peaches, plums, apricots, etc. an endocarp is thick and hard. In dry fruits, it represents the hard cover enclosing the kernel of pecans, walnuts, etc., which is separated before consumption.
Fruits can be of two kinds (true and false), depending upon the origin of the pericarp. In the majority of fruits, pericarp or the edible portion of fruit flourish from the ovary, and called as true fruits or eucarp. For instance, mango is a true fruit that develops from the mature ovary.
On the contrary, the pericarp of some fruits is formed from the plant tissues or floral parts except for the ovary and known as false fruits or pseudocarp. For instance, Apple is a spurious or false fruit that develops from the flower thalamus.
Besides, there is another kind of class of parthenocarpic fruits that are sterile i.e. lacks seed. To exemplify, banana is a parthenocarpic fruit considering as “true fruit” that develops from the ovary or only contains pericarp.
Fruit pericarp mainly helps in seed dispersal and its protection.
Pericarp comes in various colours and exudes a delectable odour that significantly helps in seed dispersal. Fruits can be dry and fleshy, so the medium of seed dispersal differs accordingly.
Dry fruits can have hard or fleshy counterparts that generally disseminate via physical factors. Seeds are ejected by pod-shattering when it attains maturity, then disperse through the wind, and thereby adhere to the animal body for transport (epizoochory).
On the other hand, the dispersal mechanism in fleshy fruits is quite different, which often depends on animals or birds those intake the fruit (endozoochory) and disperse the seeds after ingestion and excretion.
In addition to seed dispersal, an innermost layer or periplasm plays a pivotal role in seed sustenance during its developmental stages. As we have studied that an endocarp is in the closest vicinity towards the seeds that are connected to the placental layer of ovary through an umbilical structure termed as funiculus.
The funiculus appears stalk-like and attaches to the placenta on the ovary wall, once it reaches the layer of the seed coat. When the fruit attains maturity, the placental layer of the plant ovary eventually gets fused with the endocarp.
The endocarp layer often modifies into a hardened pit that protects the seeds from disease and herbivory. Despite this, it also nurtures the seed during its growth by maintaining the favourable micro-climate.