Lythraceae, the loosestrife family.
Plant: Spikes of bright pink/purple flowers on upright stems with opposite leaves. Can be up to 4' tall but is often less. Perennial.
Flowers: Bright pink/purple, 1/2'-3/4' wide. Densely clustered on spike. Usually five or six long, somewhat wrinkled petals. Some with long stamens. Flowers are somewhat variable with respect to number of petals, and stamen and pistil length.
Leaves: Opposite, lanceolate, smooth-margined, stemless, to 4" long. Sometimes clasping the stem. Stems and lower leaves with downy hairs.
Fruit: Dry husk.
Blooming: June - September.
Habitat: Wet meadows, wetland borders.
Very showy species introduced from Europe, where it rarely reaches
the heights seen in North America, possibly due to lack of natural
predators/parasites/diseases. Often seen in spectacular masses on wetland boundaries.
Unfortunately, it also crowds out native species that are more beneficial
Where to find it:
Found around the entire perimeter of the pond, most densely on the northwest
side where there are some spectacular stands. Usually close to water,
but spread well away in a few locations.
In the last few years some of the stands have exhibited a mid-summer die-off,
and look unhealthy. I don't know if there is some native disease after all, or
if something has been introduced in an attempt to control the species.