This appears to be a type of mutation called proliferation, and it can be somewhat common in certain plant groups like the daisy family (the large group that sunflowers belong to). Sometimes the mutation is temporary, occurring in certain blooms but not every flower in every year. If it does start to occur more frequently and more prominently in an individual plant (for perennials that survive the winter, that is), it might be due to a virus-like infection, in which case the affected plant may need replacing. For now, though, it's an interesting curiosity and the plant can be enjoyed as-is, especially since it's an annual.

Miri

You're welcome, and thank you! That is indeed an interesting flower.