What has happened to my sunflower?

Managed to uproot it and nothing untoward to my untrained eye to see in the roots. By the way, does anyone know which sunflower this is? Some time ago I bought a lot of mixed seeds and don't have the name. It's really nice, or would be, with it's multi-branching nature.

 

I grew some this year, kind of multi headed and darker flowers than the norm,think they we just sunflowers mixed.

 

I used Bird Seed from Wilko to grow mine this season.

 

Well now, I removed all the side-branches with buds close to emerging from the wilting plant, put them in water, and, as you can see, they're nearly all out.