Biol 324 Introduction To Seed Plant Taxonomy
Fruits: a ripened pistil, sometimes with accessory parts.
- They range in complexity from a single carpel, such as a pea pod, to a syncarpous ovary like a tomato
- We commonly call more complex structures, which may have multiple ovaries and additional edible components, a “fruit”:
e.g.
- accessory fruits (false fruits) like strawberry (the flesh of the receptacle is the red and juicy bit, the true fruits are the small yellow achenes on its surface)
- syncarps like a pineapple (this "fruit" is an entire inflorescence – made up of many flowers). The "fruit" in pineapple is therefore an entire inflorescence, including ovaries (fruits in the strict sense) from many flowers, floral parts, bracts, and the inflorescence stem, all fused into a single juicy mass.
Fruit morphology:
- Pericarp is the ripened ovary wall, i.e. the body of the fruit developed from the ovary wall. If it is divided into two or three anatomically distinct layers, they are called the exocarp (outer), mesocarp (middle), and endocarp (inner).
- Parts of the gynoecium may abort in fruit development. E.g. the flower of the coconut has a 3-carpellate, 3-loculed ovary, but only one carpel develops into the mature nut. Remains of the abortive carpels form part of the endocarp of the fruit (three scars at the bottom – remains of the vascular supply to the ovary).
Fruit classification:
There is no easy way to classify fruits as their morphology is immensely varied. However the following axes of variation are useful:
- simple vs compound pistil. Are they derived from a single carpel (e.g. a legume) or many carpels united (e.g. a berry such as a tomato)
- dry vs fleshy (e.g. a capsule of poppy versus a berry of a tomato)
- dehiscent (splitting open to release the seeds) vs indehiscent (not splitting open).
These characters are correlated with the method of dispersal of the fruits:
- by wind (anemochorous)
- attached to the outside of an animal (fur, feathers, or muddy feet - epizoochorous),
- eaten by an animal (endozoochorous)
Major fruit types:
True fruits
- Dry, indehiscent fruits. 1-seeded: achene, samara, nut, grain (caryopsis). Multiple seeded: schizocarp (splits into dispersal units called mericarps: e.g. nutlets of Lamiaceae)
- Dry, dehiscent fruits: Follicular: (1 carpel): follicle, legume, loment. Capsular: (several carpels): capsule, silique and silicle
- Fleshy fruits: drupe (fleshy and woody), berry (fleshy), pome (includes receptacle tissue)
False fruits
- Accessory fruits - are derived from ripened ovaries and non-ovarian tissue such as receptacle, hypanthium, or calyx. A strawberry is an example; most of the tissue is receptacle. The true fruits are achenes, the little "seeds" on the "berry".
- Aggregate fruits- are derived from several pistils in a single flower, for example blackberries and raspberries.
- Multiple fruits - are derived from several flowers, usually a whole inflorescence (pineapples, figs, mulberries, breadfruits)
Examples of false fruits:
Accessory fruit: strawberry, apple (in both cases the non-ovarian tissue is receptacular in origin)
Aggregate fruit: raspberry, blackberry (formed from a collection of pistils in an apocarpous flower)
Multiple fruits – syncarps: pineapple, figs, mulberry ( formed from the products of many flowers)