A Carpel consists of an ovary, a style and a stigma. A flower may have 1 or more carpels that collectively make up the Gynoecium, the female part of the flower, which is called the Pistil. The carpels may be arranged in three different ways – Monocarpous, Apocarpous or Syncarpous – as explained below, and this is a diagnostic feature used in plant identification.
Monocarpous – It has one carpel. Examples are Wild Cherry, shown here, Common Hawthorn and most Legumes.
Apocarpous – It has more than one carpel but the carpels are ‘free’ as in the Hellebore shown here with 5 free carpels. The Buttercup and Stonecrop families have free carpels as has the Rosa and Fragaria (strawberry) genera.
Syncarpous – It has more than one carpel but they are ‘united’ (sometimes called ‘fused’). The Hypericum shown here has 5 ‘united’ carpels with 5 free styles. 80% of flowering species have syncarpous ovaries.