For the past couple of years we’ve had windflowers growing in clumps, one or two metres in diameter, in our garden.
As you can maybe just make out below on the left, they seem to have spread from the meadow and woods next door.
Windflowers are a kind of anemone. According to Wikipedia they’re deadly poison, but the goats love them.
Once we had so many, I was able to see that they got their name from the way the white flowers shake and shimmer in the slightest breeze.
A Bad Guide 
Beautiful! How long do they stay in bloom? I need to plant things in my garden (to make it look like a real garden), preferably perennials, and I might look for those.
Not terribly long. A couple of weeks, I suppose.
The Wikipedia article says it’s European, but there’s also a picture of one growing in Nashville. It’s perennial, and because it’s in the lawn it gets mowed all summer without any harm being done. I do wish I could just give you some!