Fruit

Most people think of fruit as something fresh from the market, or canned or frozen, to which you may want to add sugar before eating. However, fruit can be so much more. The key to understanding the diversity of fruit types is to know that there are many different strategies for seed dispersal. Fruits follow flowers in the life cycle of a flowering plant. They are part of the sporophyte and are diploid. A fruit develops from the ovary of a flower after pollination and ovule development have occurred. Fruit functions, not only to surround and protect the developing seeds, but more importantly, to accomplish dispersal. There are many strategies of seed dispersal, including being carried by wind, water, or animals or even being eaten by animals. Words used to describe seed dispersal usually end in –chory and include anemochory for wind dispersal and epizoochory for being carried on the outside of an animal as well endozoochory for being carried in the gut of an animal. Try to guess the mode or strategy of seed dispersal for the following fruits.

FRUIT

cocklebur

maple

coconut

Blueberries are an example of a simple fruit. One fruit develops from the ovary of each flower. A first step in categorizng fruit types is to decide whether the fruit is simple (derived from one carpel or the fused carpels of a single ovary of a single flower), aggregate (derived from several separate carpels of a single flower), or multiple (derived from the ovaries of several flowers).

Pineapple A multiple fruit

Strawberry (not a true berry)

Accessory fruit

Fruits can also be categorized as accessory or not. True fruit (pericarp) develops from the wall of the ovary and any other tissue involved is considered accessory. Strawberries are accessory fruits because the flesh edible part develops from the receptacle portion of the stem of the flower rather than the ovary wall. It is also an aggregate fruit!

FLESHY FRUITS Berries are simple fruits in which all 3 layers (exocarp, mesocarp, and endocarp) of the pericarp are soft or fleshy, as in grapes and tomatoes. Seeds of berries can usually resist digestion and can be transported in the gut of an animal. See the next two slides for different types of berries.

A pepo, like the watermelon or any other squash, is a berry with a hard exocarp.

A hesperidium, as in the citrus fruits, is a berry with a leathery exocarp.

Drupes, as in peaches and plums, are fruits with a stony and inedible endocarp. Whereas an animal may eat a berry and transport seeds in their gut, drupe seeds are protected by the inedible pit and are usually discarded and left behind after the rest of the fruit is eaten.

Coconut is an interesting kind of drupe with a fibrous mesocarp for water dispersal and an endosperm within the seed that comes in both a solid and a liquid form. Most of us never see coconuts until after the fibrous exocarp and mesocarp (husk) have been removed.

A pome is a kind of fleshy fruit in which the pericarp (from the ovary wall) forms a papery core that surrounds the seeds. The fleshy, edible portion of the fruit develops from specialized stem tissue, called the hypanthium (of a perigynous flower). Pomes, by definition, are accessory fruits!

drupe caryopsis

DRY FRUITS All of the above fruits are classified as fleshy. Other fruits are dry at maturity. A caryopsis, like corn and other grains, is a simple, dry, and single-seeded fruit in which the pericarp is tightly fused to the seed coat. A corn kernel is not jut a seed, but an entire fruit.

nut samara nut achene

DRY INDEHISCENT FRUITS Other dry fruits that are also indehiscent (do not split open to release seeds at maturity) include the wind dispersed samara, the single-seeded achene with the seed attached at a single point inside the fruit (shell of a sunflower seed), and a nut with its single, unattached seed.

legume follicle capsule

DRY DEHISCENT FRUITS Some dry fruits split open to release seeds at maturity and are therefore termed dehiscent. These include the legume that splits on two sides (like a peanut), the capsule (like okra) that splits in several places - one split per carpel, and the follicle that splits on one side only.

Categories of simple vs. aggregate vs. multiple can be combined with other categories of fruit type. The so-called “cones” of sweetgum and magnolia are actually aggregate follicles.

Strawberries are aggregates of achenes with accessory tissue!

Here is an outline of all the fruit types you are responsible for: I. Simple vs. aggregate vs. multiple II. Accessory vs. non-accessory III. A. Fleshy 1. berry a. pepo b. hesperidium 2. drupe 3. pome B. Dry 1. indehiscent a. caryopsis b. samara c. achene d. nut 2. dehiscent a. legume b. capsule c. follicle