Gynoecium

Select from the following gynoecium features and view high quality images depicting the feature.

When you are ready, test your understanding and take the gynoecium quiz (see note below).

About the Carpel

The gynoecium is the female part of the flower, consisting of one or more carpels.

The carpel is a unit of the gynoecium consisting of ovary, style and stigma:Cross section diagram showing carpel Structure

  • Stigma: the area at the distal end of the style that is usually sticky so that it can capture pollen grains.
  • Style: After capture compatible pollen grains germinate and the pollen tube grows down the style transporting the generative nuclei towards the ovary.
  • Ovary: usually swollen basal part of the carpel that houses the ovules (become seeds after fertilisation) that are located within a cavity called the loculus (also known as a locule). In the plural form these words are loculi
    and locules, respectively.

Illustration from Clarke, I. & Lee, H. (2003) Name that Flower, Melbourne University Press, Victoria.

Carpels are the basic units of the gynoecium and may be free (distinct) or fused (connate). The term pistil is used in a similar manner to carpel – in some situations the terms are equivalent in meaning but not in others. For example, a flower represented by G 1 has a single carpel or a single pistil. A flower represented by G (3) represents three fused carpels but is only a single pistil (compound).

In a floral formula this would be expressed G3_

One flower with

  • 3 carpels, free (distinct)
  • 3 simple pistils

In a floral formula this would be expressed G3_

In a floral formula this would be expressed G(3)_

One flower with

  • 3 carpels, fused (connate)
  • 1 compound pistil

In a floral formula this would be expressed G(3)_

If the above is confusing the simplest path is just to use the term ‘carpel’ and avoid the potential ambiguity of using ‘pistil’.

About the Ovary

We need to determine if the ovary is superior or inferior.

To determine this a longitudinal section of the flower is needed.

Slideshow examples of superior ovary

If the sepals, petals and stamens, or their united bases (floral tube), arise from below the ovary it is superior. If the sepals, petals and stamens are free from each other the flower is hypogynous (compared with perigynous and epigynous.

In a floral formula a superior ovary is often depicted as follows, e.g. G (3) _. To remember whether the line goes above or below the number it can be useful to consider the number represents the ovary and the line as the point of attachment of the other floral parts.

Cross section diagram of a Superior Ovary

Illustration from Clarke, I. & Lee, H. (2003)  Name that Flower, Melbourne University Press, Victoria.

Slideshow examples of inferior ovary

In an inferior ovary the sepals, petals and stamens, or their united bases (floral tube), are attached to the top of the ovary. In a floral formula the line goes above the G number, e.g. G (3)¯.Cross section diagram of an Inferior Ovary

Illustration from Clarke, I. & Lee, H. (2003) Name that Flower, Melbourne University Press, Victoria.

Slideshow examples of semi-inferior ovary

In a relatively small number of species the sepals, petals and stamens arise about halfway up the ovary and this is termed half- or semi-inferior.

Cross section of a Semi Inferior ovary

Illustration from Clarke, I. & Lee, H. (2003) Name that Flower, Melbourne University Press, Victoria.

We also need to determine the number of carpels and the number of loculi in the ovary.

The carpel number can usually be determined by a cross section of the ovary.

Slideshow - Single flower with multiple free carpels

Slideshow - Single ovary with multiple fused carpels

Slideshow - Single ovary with a single loculus

Cross section diagram showing how to determine Carpel Number

Illustration from Clarke, I. & Lee, H. (2003) Name that Flower, Melbourne University Press, Victoria.

We need to determine whether the style is terminal or gynobasic.

In most species the style extends from the top of the ovary. In some families (e.g. Lamiaceae and Rutaceae) the ovary is lobed and the style is inserted between the lobes.

View terminal style slideshow

View gynobasic style slideshow

Interpreting the gynoecium part of a floral formula

  • G1_: one ovary, one loculus, superior (1 free carpel)
  • G1¯: one ovary, one loculus, inferior (1 free carpel)
  • G3_: three free ovaries each with its own stigma and style, each ovary with a single loculus, superior (3 free carpels)
  • G(3)_: this represents a superior ovary with 3 fused carpels but various structural combinations could apply, e.g.:
    • one ovary, most commonly the ovary will have 3 loculi,
    • one ovary with a single loculus but with 3 placentas and/or 3 styles or 3 stigmas, or
    • 3 free ovaries but united by a single style.
  • G∞_: more than 10 free ovaries each with its own stigma and style, each ovary with a single loculus, superior (numerous free carpels)
  • G0: indicates a sterile flower or where the flower is functionally male only
  • G(-3-) or G-(3)-: this format can be used to indicate a semi- or half-inferior ovary

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