Gynoecium - a guide to floral structure

What is the difference between a carpel and a pistil?

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’.