Purple Loosestrife (Lythrum salicaria).
Also called Spiked Loosestrife and a number of less
polite names, this is one of our most attractive
ecological disasters. Purple Loosestrife is a simply
glorious flower that can invade wetlands and displace
everything else. This stand was growing by the
Allegheny in O’Hara Township, where it was blooming in
the middle of September.