Several kind of citrus, the most common hesperidium, cut open and ready to eat.
A hesperidium (plural hesperidia) is a modified berry with a tough, leathery rind. The peel contains volatile oil glands in pits. The fleshy interior is composed of separate sections, called carpels, filled with fluid-filled vesicles that are actually specialized hair cells.
The outer ovary wall becomes the thick spongy layer, while the inner ovary wall becomes very juicy with several seeds.
Unlike most other berries, the rind of hesperidia is generally not eaten with the fruit because it is tough and bitter. A common exception is the kumquat, which is consumed entirely.
The outermost, pigmented layer of rind contains essential oils and is known as the flavedo. When scraped off and used as a culinary ingredient it is called zest. The inner rind (known as pith or albedo) of the citron or lemon is candied in sugar and called succade.