Fruits may be classified based on the arrangement from which they derive: (1) simple fruits, (2) aggregate fruits, (3) multiple fruits,
Simple fruits are fruits that develop from a single or compound ovary with only one pistil (of a single flower). Simple fruits may either be fleshy or dry.
Fleshy fruits have a mesocarp that is at least partially fleshy at maturity. The ovary may be simple, meaning derived from one modified leaf called a carpel, or compound. The ovary also may be superior or inferior and may develop into a fruit with or without other flower parts integrated.
- Drupe— Drupes are simple fleshy fruits with one seed encased in a stony pit. Usually, the ovary is a superior ovary with one ovule. The stone fruits—cherries, peaches, olives, apricots, and almonds—are examples. Although not readily recognized as a fleshy fruit, coconuts are drupes. The husk is the mesocarp and exocarp which is generally removed before making it to the market. The pit with the watery seed endosperm is what we see piled up at the store.
- Berry—These develop from a compound ovary and usually contain multiple seeds. It is difficult to determine the three regions. This group is broken down further into three types of berries:
True berries are fruits with a thin skin and a pericarp. They are generally soft at maturity and usually have multiple seeds although dates and avocados are notable exceptions. Some berries have incorporated flower parts which can be seen in remnant as scars. Examples are tomatoes, grapes, peppers, blueberries, cranberries, bananas, and eggplants. Note that botanically speaking raspberries, strawberries and blackberries are not berries. Pepos are berry fruits with thick rinds. They have multiple seeds and include pumpkins, watermelons, cantaloupes, and squashes. Finally, the hesperidium is a leathery skinned berry that contains oils. Saclike outgrowths of the inner ovary wall become filled with juice as the ovary matures. All members of the Citrus Family produce hesperidium fruits.
- Pome—The majority of the flesh in pomes comes from the swollen receptacle that grows up and around the ovary (inferior ovary). The seeds are encased by a leathery or papery endocarp. Apples are good examples. The apple core is the ovary with seeds and the rest is an overgrowth of the receptacle. (Sometimes these fruits that are derived from more than the ovary are called accessory fruits.) Examples of pomes include apples, pears, and quinces.
Dry fruits have a mesocarp that is dry at maturity. Dry fruits that split at maturity distinguished by the way in which they split:
- Follicle—Splits along one side or one seam. Ex: larkspur, milkweed
- Legume—Splits along two sides or seams. Ex: Peas, beans, kudzu, peanuts, carob
- Silique—split along two sides or seams, the difference from legumes is that the seeds are carried on a central partition which is exposed upon splitting. Ex: Mustard Family, including broccoli, cabbage, radish, watercress
- Capsule—Most common of splitting dry fruit. Composed of two carpels and split in a variety of ways: along carpel partitions, through carpel cavities, pores, or via a cap that pops off to release seeds. Ex: irises, poppies, orchids, violets, and snapdragons.
Dry fruits that do not split at maturity: the single seed is more or less united with the pericarp.
Other kinds of dry fruits are as follows:
- Achene—the seed is attached to the pericarp (husk in this case) only at the bottom and can be separated easily. Ex: sunflower seeds (husk, plus edible seed constitutes the achene), buttercup, and buckwheat.
- Nut—the pericarp of nuts are generally harder than the achenes, although they are otherwise quite similar in structure. Nuts develop with a cup or cluster or bracts at their base. Ex: hazelnuts, hickory nuts, and chestnuts. Note that botanically speaking most things called ‘nuts’ are not nuts such as peanuts (legume), coconuts, almonds, walnuts, pecans (all drupes) Brazil nuts (capsule) and pistachios (drupes). Yet another misnomer commonly accepted.
- Grain—Grains are all of the Grass Family and feature a pericarp that cannot be separated from the seed. Ex. Corn, wheat, barley, rice, and oats. The grains are also called caryopses.
- Samara—pericarp extends as a wing or membrane which aids in dispersal. Usually, samaras are produced in pairs, although elms and ash trees produce them singly. These are the ‘helicopters’ that I am certain we all have played with at one point or another. Ex: maple trees
- Schizocarp—schizocarps are the twin fruits, as at maturity the fruit dries out and breaks into two one-seeded segments. Ex: carrots, dill, parsley, and anise.