When most people think of a fruit, what typically comes to mind is a juicy edible object, such as an apple, orange, or banana. To botanists, however, fruit includes many plant-derived structures, such as grains, nuts, and many vegetables. In essence, a fruit is an enlarged ovary, often with some accessory tissue, that develops after a flower has been pollinated. After pollination, seed development begins, and soon the peripheral parts of the flower fall away, leaving the immature fruit. The fruit subsequently enlarges and then ripens to maturity. It is then often edible.
Almost all fruits have a general structure that consists of an outer layer called the pericarp. The pericarp, in turn, encloses the seed or seeds. Usually there is a space between the seed and the pericarp, called a locule. The pumpkin is a good illustration of this structure, with orange rind as the pericarp, the hollow space within the locule, and the seeds inside the locule.
There are many different kinds of fruits. Some, such as cherries, tomatoes, and apples, have fleshy, juicy pericarps. Others, such as peanuts, milkweed pods, and acorns, have dry pericarps. The variability in fruits represents different seed dispersal strategies. In some plants, the seeds are dispersed while still enclosed within the fruit. Seeds in fleshy fruits are often dispersed by animals that eat the fruit and then either discard the seeds or later defecate them. Other fruit have barbs or hooks that catch on to fur or feathers and then travel with an animal until they are removed or drop off. Still other seeds, such as those of maple and ash, have “wings” for wind dispersal. A few, such as those of the coconut palm and many types of sedge, have fruits that float and are dispersed by water. In most instances, the fruit merely opens, and the seeds drop onto the ground. Some plants, such as witch hazel and the touch-me-not, produce fruits that open explosively and can disperse their seeds great distances.
Fruits can be classified, based on the nature of the pericarp, into two groups: fleshy and dry. Fleshy fruits, in turn, are classified into several types, including drupes, berries, pomes, hesperidia, and pepos. Dry fruits are also subdivided into several categories, including follicles, legumes, capsules, achenes, nuts, samaras, schizocarps, and caryopses.