The structure known as a "fruit" is found only in the members of the Angiosperms. A fruit developed solely from the ovary and its contents is known as a true fruit. A fruit developed from the ovary and its contents plus additional parts of the flower such as the receptacle, petals, and sepals is known as an accessory fruit (e.g. pineapple). The following is a common classification of fruit types. (see pp. 489-493 in Plant Systematics, 2nd ed., for additional information).
I. Simple Fruits - Fruits formed from 1 pistil. They may be either true or accessory fruits.
A. Dry Fruits: - Fruits in which the coat becomes dry at maturity.
1. Dehiscent Fruits - Dry fruits which at maturity open by definite natural means to shed the contained seeds.
i. Legume A dry dehiscent fruit developed from 1 carpel and at maturity splitting along both the dorsal and ventral sutures. (beans, peas).
ii. Follicle A dry dehiscent fruit developed from 1 carpel and at maturity splitting along only one suture. (larkspur, columbine)
iii. Capsule A dry dehiscent fruit developed from several carpels.
(a) Loculicidal capsule - one which splits along the outer median line. (lilies).
(b) Septicidal capsule - one which splits along the septa and opens at the top. (yucca, agave).
(c) Silique - a special long slender capsule of 2 carpels. (mustards).
(d) Silicle - a special short broad capsule of 2 carpels. (mustards).
(e) Pyxis - a capsule which has circumscissle dehiscence. (plantain, amaranths, purslane).
(f) Poricidal capsule - one which opens with round holes. (poppies).
2. Indehiscent fruits - Dry fruits which do not open when mature to shed their seeds. Many of this group are one seeded fruits.
i. Achene - A one-seeded, dry, indehiscent fruit; the one seed is attached to the fruit wall at a single point. (buttercups, dandelion, sunflower).
ii. Nut - A dry, indehiscent, one seeded fruit similar to an achene but with the wall greatly thickened and hardened. (beech, chestnut, oak, hazel; walnut and hickory - note: because of extrafloral bracts, or "husk", the latter two fruits are sometimes called "drupes").
iii. Samara - A one- or two-seeded dry, indehiscent fruit in which part of the fruit wall grows out into a wing. (elm, maple, ash).
iv. Grain - A one-seeded dry, indehiscent fruit in which the fruit wall and the seed coat are fused. (wheat, corn, grasses).
v. Schizocarp - A fruit formed from several carpels, each carpel of this pistil enclosing a single ovule, at maturity the carpels separate as separate indehiscent fruits. (mallow, wild carrot, dill).
B. Fleshy Fruits - A fruit in which the wall becomes soft and fleshy as it matures.
1. Drupe - A one-seeded simple fruit developed from a superior ovary in which the innermost portion of the wall (endocarp) becomes hard and stony, the outermost part (exocarp) becomes a relatively thin skin, and the middle portion between the skin and the stone (mesocarp) becomes either fleshy or fibrous. (cherry, coconut, walnut and hickory - note: because of extrafloral bracts, or "husk", the latter two fruits are sometimes called "drupes", but best called "nuts").
2. Berry - A simple fruit in which the ovary wall or at least its inner portions become enlarged and usually juicy. (grape, banana, gooseberry).
Two special types of berry-like fruits may be singled out for special consideration.
(a) Hesperidium - This is a special type of berry in which a leathery rind forms; the interior of the fruit divided by septa, indicating the number of carpels. (citrus).
(b) Pepo - This is a special type of berry in which a relatively hard rind is formed; the interior of fruit not divided by septa. (watermelon, gourds, squash).
3. Pome - An accessory fleshy fruit formed by a group of carpels more or less firmly united with each other and surrounded by and united to the floral tube or receptacle. (apple, pear, mountain ash).
II. Aggregate Fruit - A fruit formed by the development of a number of pistils from the same flower. The individual units may be berries or other specific types. (raspberry, strawberry).
III. Multiple Fruit - A fruit formed by the development of a number of pistils often with accessory parts, the pistils being from a number of flowers. (mulberry, fig).