At the start of this year, I bought a few vegetable seeds via a webshop. As an extra, I got a packet of 10 free sunflower seeds. I don't recall the variety name, but it was a pretty standard variety.

I planted all of them in a seed tray, 8 of them germinated and were planted out. They all reached heights of at least 2 meters (6-7ft), and one the respectable height of 10 ft. Now the 'weird' part. Of those eight sunflowers, 2 of them decided one flowerhead wasn't enough. The 10ft long one currently has about 15 flowerheads, one big one at the top as usual and the others at the leaf nodes. Every leaf get's its own flowerhead. It looks great, but it seems to be rare because everyone is amazed by it.

Then there's a third sunflower, with weird seeds. They are very dark purple, and have a kind of husk or fleece around them, which I can scrape of very easily with my nails. If I do so, my fingers are stained purple. The rest of the plant is similar to a standard yellow sunflower.

Any ideas what's happening here? I've read that multiple flowerheads on a sunflower might be caused by poor soil, which is plausible but that doesn't seem to comply with their length.