epicarp n : outermost layer of the pericarp of fruits as the skin of a peach or grape [syn: exocarp]

English

Noun

1. exocarp

A fruit in botany it is referring to a mature ovary. In fleshy fruits, the outer, often edible layer is the pericarp, which is the tissue that develops from the ovary wall of the flower and surrounds the seeds. While the seeds are akin to the eggs developing in the ovary of a fowl, the pericarp may be assumed as the uterus.

However, there is a small number of fruits which do not fit into that description; for example in most nuts and legumes the edible part is the seed and not the pericarp. Many edible vegetables are actually stems, leaves, and even roots of the plant, while others like the cucumber, squash etc. are common pericarp and are botanically considered as fruits. Lastly in some seemingly pericarp fruits the edible portion is actually an aril.

Categories of fruits

Fruits come in three main anatomical categories:

• Simple fruits are formed from a single ovary and may contain one to many seeds. They can be either fleshy or dry. Examples for simple fleshy fruits are berries, drupes and pomes. Examples for dry fruits include nuts and grains.

• Aggregate fruits are formed from a single compound flower and contain many ovaries. Examples include raspberries and blackberries.

• Multiple fruits are formed from the fused ovaries of multiple flowers. An example for a multiple fruit is pineapple.

Anatomy of simple fruits

In berries and drupes, the pericarp forms the edible tissue around the seeds. In accessory fruits, other tissues develop into the edible portion of the fruit instead, for example the receptacle of the flower in apples and strawberries.

Pericarp layers

The pericarp itself is typically made up of three distinct layers: the exocarp which is the most outside layer or peel, the mesocarp the middle layer or pith, and the endocarp the inner layer surrounding the hollowed ovary or the containing seeds.

Exocarp

Exocarp (Gr. "outside" + "fruit"), is a botanical term for the outermost layer of the pericarp (or fruit). The exocarp forms the tough outer skin of the fruit which bears oil glands and pigments. The exocarp is sometimes called the epicarp, or, especially in citruses, the flavedo.

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

In citrus fruits, the flavedo constitutes the peripheral surface of the pericarp. It is composed by 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 state, contained chlorophyll. This is responsible for the fruit's change of color from green to yellow upon ripening.

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

Mesocarp

Mesocarp (Gr. "middle" + "fruit") or Sarcocarp (Gr. "flesh" + "fruit"), is the botanical term for the succulent and fleshy middle layer of the pericarp of drupaceous fruit, between the exocarp and the endocarp; it is usually the part of the fruit that is eaten.

The second term may also refer to any fruit which is fleshy throughout. In a hesperidium, the mesocarp is also referred to as albedo or pith because of its soft fiber. By most of them it is part of the peel which is peeled off by hand.

Endocarp

Endocarp (Gr. "inside" + "fruit"), is a botanical term for the inside layer of the pericarp (or fruit), which directly surrounds the seeds. It may be membranous as at citrus where it is the only part consumed, or thick and hard as in the stone fruits of the subfamily Prunoideae such as peaches, cherries, plums, and apricots.

In nuts, it is the stony layer that surrounds the kernel of pecans, walnuts etc. and which is removed when eating.

Anatomy of grass fruits

The grains of grasses are single-seeded simple fruits where 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.

See also

• Peel (fruit)
• Hesperidium the common citrus berry.

References

• Citrus fruits - contains diagram, although the page itself appears to have been poorly translated from another language