Section D – Reproductive anatomy
D4 Fruits
Fruit structure The true fruit is a feature only found in the flowering plants since it is formed, at
least in part, from the carpel(the so-called ‘fruits’ of conifers such as yew or
juniper are fleshy outgrowths from the seeds or cone scales). There are
numerous different shapes, sizes and types of fruits, from water melons and
pineapples to dehiscent pods and the dry chaff of a grass. They have been classi-
fied in several different ways according to the structures that give rise to them.
These always involve the ovarieswhich may be free or fused, superior or infe-
rior. Sometimes the rest of the carpel develops into part of the fruit as well and
other floral parts such as the basesofsepalsorpetals, or the receptaclemay be
involved. A few fruits such as the fig and pineapple are derived from a whole
inflorescence.
Dehiscentfruits, i.e. those which open to disperse their seeds (Fig. 1), usually
have several seeds and the fruit itself often has a protective function as the seeds
mature. It may derive from a single carpel as in the pods of peas and other
legumes, or from two or more fused together, as in Arabidopsis(Topic E1) and
other members of the cabbage family. The outer fruit wall is normally hard and
contains one or more layers of sclerenchyma cells mixed with parenchyma,
sometimes with the cell layers at different angles. As they dry out the cell layers
dry differentially. Lines of weakness occur along the carpel margin or where
several carpels fused and these break to disperse the seeds. In many legumes,
Key Notes
Fruits are formed from the ovary and sometimes other parts of the carpel
or other parts of the flower. Dehiscent fruits usually have a hard wall
made partly of sclerenchyma and break along a line of weakness where
fusion has happened.These may be dry and resemble the seed coat in the one-seeded fruits of
grasses and some other plants and dispersed with the seed. Fleshy fruits
are variable, some with a complex structure with a separate rind, layers
of different cells and juice-filled parenchyma. When immature, the fruits
are often photosynthetic, becoming colored and often with an increase in
sugar as they mature.Many dehiscent fruits simply drop their seeds and have no specialized
dispersal. Fleshy fruits may be ingested by vertebrates and the seeds
dispersed through defecation or by the animal discarding them. Other
indehiscent fruits form burs. Some are dispersed by wind forming a sail.
In composites the sepals increase in size to form a feathery dispersal
structure.Related topics The flower (D1) Plants as food (N1)
The seed (D3)Fruit structureIndehiscent fruitsDispersal