Plants and People. Fruits. ovule. locule. The Carpel . The carpel is the basic unit of the gynoecium. Each carpel consists of an ovary connected to a stigma by the style.
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The carpel is the basic unit of the gynoecium. Each carpel consists of an ovary connected to a stigma by the style.
Within within each carpel are one or more ovules, which will become the seed(s). The area of attachment is called the placenta (pl. = placentae) and the empty space in the chamber is called the locule (pl. = locules). The dividing walls are called the septa.
A gynoecium with only one carpel is termed unicarpellate. A gynoecium of many separate carpels is termed apocarpous.
A gynoecium with many fused carpels is termed syncarpous and the flower is said to have a compound pistil.
Evolution of the fused carpel
basal placentation: attachment of ovules to the bottom of the ovary. One locule, no septa. Can be found in an apocarpous or syncarpous gynoecium.
apical placentation: The attachment of the ovules is at the apex (top) of the ovary. One locule, no septa. Can be found in an apocarpous or syncarpous gynoecium
parietal placentation: ovules are attached to the side walls of the ovary (or extrusions of the wall) such that an ovary usually has one locule and therefore no septa. Can only be found in a syncarpous gynoecium;
axile placentation: ovules are attached to an axis derived from the connate margins of the component carpels, such that an ovary is divided into two or more locules by septa. The ovules are borne along the central axis. Can only found in a syncarpous gynoecium.
free or central placentation: attachment of ovules to a free-standing central column in a syncarpous, unilocular ovary (one locule, no septa)
marginal placentation: ovules are attached to the folded margins of the carpel, giving the appearance that there is only one elongated placenta on one side of the ovary. Can only be found in a simple pistil. This is conspicuous in legumes.
A simple fruit is one that is derived from a single ovary, this ovary can be part of an apocarpous, syncarpous or unicarpellate gynoecium.
The ovary wall develops into the pericarp, or fruit wall. This may have three layers: the exocarp, mesocarp, and endocarp.
The pericarp can develop in various ways, leading to the assortment of simple fruit types.
Dry fruits have the pericarp dry at maturity. Fruits which split open to release the seeds are termed dehiscent. Those that do not split open are called indehiscent.
Indehiscent, dry fruits do not split at maturity.
Subclasses of indehiscent fruits:
Achene - single seeded, thin pericarp, seed coat is separate from ovary wall. Example: sunflower and strawberry “seeds”
Grain (caryopsis) - single seeded, pericarp fused with the ovary wall. Example: corn, wheat
Nut - single seeded, with hard or bony pericarp, wholly or partially surrounded by a husk of bracts. Example: hazelnut, walnut
Dehiscent fruits are characterized by the splitting of the pericarp to release the seeds.
Subclasses of dehiscent fruits:
Legume - usually dehisces along two sutures; from a simple pistil. Example: beans, peas, soybeans
one folded carpel
Legume Split Open
(1 carpel, 2 seams)
Capsule - usually from a compound pistil, usually many seeded. Pericarp opens with pores or slits. Example: okra (which we eat before maturity.)
dehisces along locules
okra is a capsule
Fleshy fruits are fruits in which all or part of the pericarp is fleshy and swollen at maturity.
Types of fleshy fruits:
Berry - one to multiple seeds, mesocarp is fleshy, endocarp is soft. Example: grape, tomato
Drupe - usually one seeded, mesocarp fleshy, endocarp usually hard. Example: peach, plum
Hesperidium - special kind of berry with leathery rind and oil glands dotting the surface. Example: lime, orange
Pepo fruits are simple fruits that are berrylike with a hard rind; almost always with three carpels and parietal placentation. Examples: melon, squash
Pome fruits are simple fruits that are berrylike with most of the flesh derived from a floral cup and receptacle. Example: Apple, pear
Other fruit types:
Multipe fruits are formed by the fusion of fruits of numerous independent flowers. Example: pineapple, fig
Aggregate fruits are those formed from several separate ovaries within a single flower. Examples: raspberry, blackberry
Accessory fruits are those where the “fruit” part is derived from something other than ovary tissue. A strawberry is a swollen receptacle and the seeds on the surface are the true fruits, called achenes.