I knew it was going to happen. Bidens aristosa is covering the Arboretum!

It is indeed a showy tickseed! If we have to be overrun, this is the way to go. Every year it turns more of the Arboretum gold in the late summer. We have acres of it now. I took these pictures a couple weeks ago (before my cornea transplant). There are sill flowers today though only hundreds of thousands, not millions. Maybe only tens of thousands. We've been watching this spread since... well since it first exploded  . It first appeared in the Fern Valley Meadow and Prairie, it's reaching into the ellipse and overtaken the triangle between the meadow and the paper birches in the National Grove of State Trees. And it's established beachheads along Springhouse Run, fields abutting Research Nurseries, and throughout the arboretum any place it finds a sunny space.