I grow this sunflower from seeds, but look at what happened to the petal, it grew in the middle. Very interesting, I have not seen anything like this before. Is this a mutation? Can anyone shed light on this?

Flowers just do weird things like that sometimes, especially sunflowers.

The flower looks fasciated first off, which is sometimes a mutation, sometimes a bacterial infection, sometimes unknown why I haven't seen ones where there are petals in the 'middle' but it is possible the floral meristem split into two and as they migrated away from the middle eventually the signals they send telling the middle to make reproductive structures not petals get weak. Not 100% sure though, sure is interesting either way thanks for sharing!

I think it's beautiful! If you could just develop a strain that does that on each flower you'd be rich.
Great picture.
Shoe

Here are 2 strange sunflowers from last summer:

similar