An aggregate fruit is a single fruit that is formed by merging the fruits of a number of ‘free’ carpels within a single flower. A carpel consists of an ovary, a style and a stigma. A fruit is a seed-bearing structure that develops from the ovary and surrounding tissue. A flower may have one or more carpels. If it has more than one carpel but the carpels are ‘free’ as opposed to being ‘fused’ together, it may merge their fruits to form a single fruit like structure. However, many flowers which have multiple ‘free’ carpels do not merge their fruits but are said to have have an aggregate of fruits.
Aggregate Fruits – the Blackberry is an example. It is made up of number of drupelets (small drupes). The strawberry is another example but it is also an accessory fruit. Click HERE for more information on accessory fruits. The clematis has an aggregate of achenes and the delphinium has an aggregate of follicles but in both cases the individual fruits are not merged together.
The flower of the blackberry may have 50-100 ‘free’ carpels at its centre (shown with white tips in this photo). Each carpel can develop into a fruit called a drupelet. The actual number of drupelets produced will depend on the number fertilised which in turn may depend on the weather and the number of visits by pollinators. In commercial studies ‘drupelet set’ ranged from 40% to 80%. Drupelet set can also be affected by viruses or fungal growth. Some species can self-pollinate if no pollinators are present.
The blackberry is the fruit of the Rubus genus. It is an aggregate fruit because it is made up of a number of drupelets (small drupes). This photo shows a single blackberry. The raspberry is also an aggregate fruit.
This photo shows the fruit of a Clematis vitalba Travellers Rest. The fruit is an aggregate of achenes.
This photo shows the fruit of a Delphinium which is an aggregate of follicles.