Plant Structures: Fruit

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questionThought Questions

Explain the science behind the following gardening questions:

1.  Why are fading flowers removed from spring flowering bulbs and other flowering ornamental plants?




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Fruit evolves from the maturing ovary following pollination and fertilization.  Fruits can be either fleshy or dry.  They contain one or more seeds.

Function

  • Reproduction
  • Horticulture uses
  • Feed, food, and oils
  • Aesthetic qualities
  • Plant identification

Structure

Fruit consists of carpels where the ovules (seeds) develop and the ovary wall or pericarp, which may be fleshy (as in apples) or dry and hard (as in an acorn).  Some fruits have seeds (mature ovules) enclosed within the ovary (apples, peaches, oranges, squash and cucumbers).  The peel of an orange, the pea pod, the sunflower shell, and the skin flesh and pit of a peach are all derived from the pericarp. 

Other fruit have seeds that are situated on the periphery of the pericarp (corncob, strawberry flesh).

Apple blossom with fruit

Figure 1.  In apples, the ovary wall becomes the fleshy part of the fruit.  Notice the small fruit structure in the blossom.


Apple fruit

Figure 2.  Pome fruit (apple)


Peach fruit

Figure 3.  Stone fruit (peach)


Fruit Types

Conifers

Conifers are best known for their woody cones, pine cones.  Junipers are an example of a conifer with a fleshy cone (Juniper berry).  Upon close examination, the overlapping scales can be observed.

Conifer fruits

Figure 4.  Fruit of conifers – Left: Woody seed cone (pine cone).  Right: Fleshy seed cone (Juniper berry).


Flowering Plants (Angiosperms)

Depending on flower structure and inflorescence type, fruits may be either simple, aggregate, or multiple.

  • Simple – Fruit formed from one ovary.
  • Aggregate – Fruit formed from a single flower with many ovaries.  If not all of the ovaries are pollinated and fertilized, the fruit will be misshapen (raspberry, magnolia).
  • Multiple – Fruit developed from a fusion of separate, independent flowers born on a single structure (mulberry, pineapple, beet seed).


Table 1. Key to Common Fruit Types

1a. Fruit fleshy. — go to 2

1b. Fruit dry at maturity. — go to 6

2a. Fruit simple, that is derived from a flower with a single ovary. — go to 3

2b. Fruit derived from a single flower with many ovaries. — Aggregate Fruit (raspberry, magnolia).  Note: If not all of the ovaries are pollinated and fertilized, the fur it will be misshapen.

2c. Fruit develops form multiple separate flowers in an inflorescence, the fruits coalesce together to form a single “fruit” at maturity.  — Multiple Fruit (mulberry, pineapple, beet seed)

Fruit type: Stone or Drupe3a. Fruit with a single seed enclosed in a hard pit.  The exocarp (outer layer) becomes the thin skin; the mesocarp (middle layer) becomes thick and fleshy; and the endocarp (inner layer) becomes a hard stony pit.  — Drupe (peaches, olives, cherries, plums)  

3b. Fruit with more than one seed, the seed not enclosed in a hard pit.  — go to 4

Fruit type: berry4a. Fruit develops from the ovary only. Pulpy fruit from one or more carpels that develops few to many seeds, inner and outer walls fleshy.  —  Berry (tomatoes, eggplant, blueberries, and grapes)


Hesperidium4a-1. Berries with a leather rind containing oils, enclosing a pulpy juice sack (carpels).  — Hesperidium (citrus: oranges, lemons, limes, grapefruit)


4b. Fruits develops from the ovary plus other flower parts (accessory fruits). — go to 5

Fruit type: Pepo5a. Simple fruits with relative hard rind at maturity, fleshy-watery interior with many seeds.  — Pepos (cucumbers, melons, and squash)


Fruit type: Pome5b. Simple fruit with several carpels and papery inner wall (endocarp) and fleshy outer wall. — Pomes (apple, pear, quince)

6a. Fruit not splitting at maturity. — go to 7

6b. Fruit splitting open at maturity. — go to 10

Fruit type: Samara7a. One-seed achene fruit (elm, ash) or two-seed fruit (maple) with a wing-like structure formed from the ovary wall. — Samaras



7b. Fruit without wings. — go to 8

fruit type: Nut8a. One-seeded fruit with hard stony shell (pericarp) surrounding the seed. — Nut (oak, filbert, walnut)


8b.   Fruit without hard shell. — go to 9

Fruit type: Caryopsis9a. Simple, one-seeded fruit with a thin seed coat (pericarp) surrounding and adhering tightly to the true seed.  — Caryopsis (corn, rice, wheat, and barley)


Fruit type: Achene9b.   Simple, one-seeded, thin-wall fruit with seed loosely attached to ovary wall.  — Achenes (sunflower)

Fruit type: Capsule10a. Fruit from two or more carpels, each with many seeds, splitting along or between carpel lines or forming a cap that comes off or a row of pores near the top. — Capsule (iris, poppy, jimson weed)


10b. Fruit splitting lengthwise along the edge. — go to 11

Fruit type: Silique11a. Fruits from two carpels with a central partition to which the seeds are attached.  Splits to expose seeds along central membrane. — Silique or Silicle (mustards)


11b. Fruits not leaving a central partition. — go to 12

Fruit type: Follicle12a. Fruit from a single carpel that splits along one suture only. — Follicles (Delphinium)


Fruit type: Legume or Pod12b. Fruit from a single carpel usually splits along two sutures.  Found in members of the Fabaceae (pea) family.  — Legumes Pod (peas, beans)


12c. Fruit formed from two or more carpels that split at maturity to yield one-seeded halves.  — Schizocarp (carrots, dill, parsley, hollyhock)



Fruit Growth Terms

  • Bud development – On temperate-zone woody plants, buds typically develop mid-summer of the previous year.  An exception is on summer flowering shrubs, where the buds develop on the current season’s wood.

  • Pollination – Transfer of pollen from the male flower to the stigma of the female flower.

  • Fertilization – Union of the pollen grain from the male flower with the egg cell in the female flower.

  • Drop – Fruit drops when not pollinated or fertilized and when too much fruit sets on a tree.

  • Growth – What we see as growth is primarily cell enlargement as the cells fill with water.

  • Climacteric – Point when a fruit will continue to ripen if removed from a plant, (for example, pumpkins turning orange after being harvested).

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Authors: David Whiting (CSU Extension, retired) with Michael Roll and Larry Vickerman (former CSU Extension employees). Artwork by Scott Johnson and David Whiting.

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Revised October 2014

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