My Gaillardia is doing something rather odd this year. This stem has to be 2 inches wide, flat, and has this bizarre bloom at the top. The other half of the plant is blooming normally Odd, isn't it?
Weird but strangely wonderful at the same time. Maybe it's some sort of virus the plant has contracted??
I have seen this before with plants that are root crowded. It was my grandmothers poppies that came up really thick and the flowers looked like, something, but not normal. We fixed it by thinning them out and fertilizing for blooms. Could be too much nitrogen too but this is just a guess. I do see a LOT of greenery and you said the stalks are alot thicker so it could be. Maybe a little too much copost or a present from a cat or dog? To be totaly honest I love the deformed ones. Look like sundew almost. Maybe you have nuclear fertilizer that is mutating them.
I hqad a different kind of flowering plant once that did that (Tanacetum 'Robinson's Red'). Another of these p-lants had fused blooms at the end of the stem (4...and ine is normal). I found out that it had had a virus that caused the mutation. I apologize, but I do not recall the type.
I saw a wild Ox-Eye Daisy doing that one time. I had a picture, but for the life of me I can't find it. Anyway, it looked like two separate flowers growing in a swirled X shape.
Hmm, I often get two strawberries that are combined, like conjoined twins... Wonder why that happens?