Botany Basics (Continued)
Fruits of Plants
Angiosperms produce seeds and fruit when fertilization occurs while gymnosperms produce only seeds. Conifers account for a large number of gymnosperms and bear seeds in cones. However, other gymnosperms bear seeds wrapped in a fleshy structure called an aril.
As a botanical term, fruits encompass all seed-bearing structures that develop from the ovary of an angiosperm or flowering plant. However, in horticultural terms botanical fruits are labelled as fruits or vegetables. Botanical fruits like corn, cucumbers, and tomatoes are considered vegetables from a horticultural perspective.
Fruits are sometimes classified based on the number of ovaries that make up the structure. When classified in this fashion, fruits are said to be simple, aggregate, or multiple.
When ovaries of flowers develop into fruit, their wall will often become thick and differentiated into three layers. Those three layers are the exocarp which is the outermost layer (often only the epidermis), the mesocarp or middle layer which varies in thickness, and the endocarp or inner layer which differs widely between different angiosperm species. The three layers together are called the pericarp which encloses the developing seed(s). The characteristics of a fruit’s pericarp can also be used to classify them. When fully mature, the pericarp can vary from fleshy to dry.
Simple fruits arise from a simple or compound ovary in a flower that has only one pistil. Some are dry while others are fleshy. There are several types of simple fruits.
Berries are simple fruits where the entire pericarp is fleshy. This includes grapes, blueberries, and tomatoes.
A pepo is a berry with a hard rind where the receptacle partially or completely encloses the ovary like cucumbers and squash.
A hesperidium is a specialized berry that has a leather rind like various citrus fruits.
Drupes or stone fruits are simple fleshy fruits derived from a single carpel and usually contain one seed with a stony endocarp. These include fruits like almonds, peaches, plums, cherries, and olives.
Pomes are simple fleshy fruits where the inner portion of the pericarp is papery forming a core. Apples and pears are examples of pomes.
The above are examples of fleshy simple fruits, but other fruits exist that are simple where the ovary walls or pericarps dry at maturity. These dry simple fruits are classified based on the fruit’s ability to split apart or dehisce once mature. Those that split open at maturity along a built-in line of weakness in the fruit and release many seeds while they are still attached to the plant are called dehiscent fruits. These include poppies and peas. Those that do not dehisce when ripe are called indehiscent fruits and include corn, sunflower seeds, and various nuts.
An aggregate fruit or etaerio is a fruit that develops from the merger of separate ovaries or pistils that were formed within a single flower. Each of the ovaries are fertilized separately which means if all ovaries are not successfully fertilized, the resulting fruit will be malformed. Blackberries and raspberries are examples of such an aggregate of individual drupes or stony fruits.
Strawberries are another type of aggregate fruit. Each seed on the outside of a strawberry originates from a single dry, ripened ovary attached to a fleshy red receptacle that has grown, softened, and turned red as the fruit matured.
Multiple fruits or collective fruits are fruiting bodies that result from a cluster of fruiting flowers or an inflorescence. While each flower produces a fruit, the pericarps of those fruits merge into a single mass as the fruit matures. Figs, pineapples, Osage-oranges, and mulberries are examples of multiple fruits.