These are probably my favorite seeds, those of the native-to-Missouri grass Chasmanthium latifolium. It has several common names like "northern sea oats", "wood oats", "Indian wood oats", and variations, but I've come to just call it "Chasmanthium".
It's especially wonderful backlit by the morning sun, isn't it?
I have dozens of this plant growing in my yard now, and I could easily imagine it transforming my lawn into a sea of gently waving foliage.
In fact I don't have to imagine this, because when biking at the nearby Castlewood State Park I saw a huge expanse of this grass growing in a lightly wooded area of the park. It was impressive, but I took it as a warning to make sure I remove lots of these seeds before the start dropping. (I'll leave some for the birds, as I've seen finches eating them before.)
Not sure why I didn't get the camera out to snap a photo of the Chasmanthium sea, but I was probably too preoccupied trying to stay on the bike on a very sandy trail.