What is this shrub in my backyard? It is very floriferous with many yellow "puffball" blooms along each stem. It is at least five feet tall and would grow to be that wide or wider if I didn't keep it in check. It doesn't have a central trunk - pretty much all of the branches are on their own "stem". (So I guess that might not make it a shrub, eh?)

Anyway, do you have any ideas what this lovely but bordering on invasive plant is? Thank you!

Here is a link that might be useful: Yellow puffballs