As the fertilized eggs and surrounding tissues of a plant ovule are maturing into seeds, the ovary surrounding them develops into a protective container called a fruit.
Fruits are so varied that it is difficult to fit all fruits into even the most detailed schemes of classification. In general, fruits are usually classified into three large groups:
- simple,
- aggregate, and
- multiple
This article examines the category of simple fruits.
What is a Simple Fruit?
The ripening of a single or compound ovary with a single pistil produces a simple fruit. The ovary may develop into a thick, soft covering termed fleshy or a thin, hard or fibrous covering termed dry.
Structure and Types of Dry Fruits
As the fruit wall ripens in simple dry fruits, it becomes leathery, papery, or woody. Dry fruits may be either dehiscent (opening to discharge seeds), or indehiscent (not opening to discharge seeds).
Simple dry fruits are categorized as follicles, legumes, capsules, achenes, grains, samaras, and nuts.
Follicle. The follicle is the most primitive type of fruit. It is derived from a simple pistil and opens along one side only. The most familiar examples are the milkweed, peonies, larkspurs, and columbines.
Legume. The legume is similar to a follicle. However, it opens along two sides. This is the characteristic fruit of the pea family. However, in some members of the family, such as the peanut, the fruit does not open at maturity and is indehiscent. A peanut is not, as it is popularly called, a nut. Rather, it is an indehiscent legume.
Capsule. The capsule is a dry fruit that develops from a compound or many-part pistil. It may split open along the back of individual segments (known as carpels) or along the line where two carpels meet. Poppies and irises are among those plants that form capsules.
Achene. An achene is a small dry fruit containing a seed. The small mature achene is commonly mistaken for a seed. However, it is technically a fruit with the seed inside. The familiar “seed” of a dandelion or sunflower is not a seed, but an achene, as are the “seeds” of strawberry.
Grain. The grain is a one-seeded fruit similar to the achene, except that the thin, usually colorless seed coat is fused with the mature ovary wall or pericarp. The seed and the fruit, therefore, merge into a single unit. The grain is the characteristic fruit of the grass family. Corn, wheat, rye, oats, barley, and rice are familiar examples.
Samara. The samara or key fruit is an indehiscent, usually one-seeded, winged fruit. Examples are the fruits of elm, ash, tree of heaven, and maple.
Nut. The term “nut” is applied to a one-seeded rather large fruit in which the fruit wall of becomes hard, stony, or woody upon ripening. Examples are the fruits of the filbert (hazelnut). beech, oak, chestnut, hickory, pecan, and walnut. In these examples, the nut is associated with structures formed from highly modified leaves known as bracts.
Structure and Types of Fleshy Fruits
Fruits in which a portion of or all the fruit wall is fleshy at maturity are classified as simple fleshy fruits. Simple fleshy fruits may be classified as berries, drupes, false berries, and pomes.
Berry. The true berry is a fruit in which the entire ovary wall ripens into a fleshy, often juicy and edible, pericarp. The botanist’ definition of a berry includes the fruits of the date, tomato, grape, avocado, eggplant, persimmon, and pepper are berries. Citrus fruits, such as orange, grapefruit, lime, and lemons are modified berries, although the pericarp (rind or peel) is not usually regarded as edible.
Drupe. In the drupe, the pericarp is divided into three parts: an outer exocarp (commonly a thin skin), the mesocarp, which is the fleshy pulp, and the endocarp, the stone or pit which encloses the seed. Examples of drupes are the olive, plum, cherry, peach, and apricot.
False Berries. False berries may usually be distinguished from true berries by the remnants of flower parts that persist at the top of the fruit, opposite the stem. At the apical end of the cranberry, for example, several small sepals can be seen. The tip of the banana fruit bears a large dark scar where the flower parts have fallen. Included in this category are the cucumber, squash, muskmelon, and other members of the gourd family, the cranberry, gooseberry, currant, and banana.
Pome. In pomes such as the apple and pear, the outer part (exocarp and mesocarp) is fleshy, and the core (endocarp) is leathery. The seeds appear in the center surrounded by the leathery endocarp.
Fruits are the protective containers that develop around the seeds of flowering plants (angiosperms). In the case of the simple fruits that develop from a single pistil, this container may be fleshy or dry.
 |
 |
 |
 |
