yes its usual, i had one with one big flower then further down five smaller flowers, dont know what causes it think we might just be used to knowing of them as single flowers. someone else might be able to help.

There are a number of different species of sunflower. The traditional one has just the one head but others have several.

Thanks for your help Catty and Bulbaholic,I think it must have been the birds that dropped a seed as it is the only one.

Our son won his village sunflower competition this year with a present from the birds!

your welcome, :)