Boneset. Eupatorium perfoliatum.
Asteraceae, the daisy, sunflower or composite family.

Plant: Hairy, upright, sparsely branched plant, 2'-4', with opposite leaves that the stem appears to pass through, and large rounded clusters of small white flower heads.
Flowers: Small white flower heads, 1/4" wide, organized into large, flat-topped clusters. From above, the heads appear to contain small holes from which white threads emerge. The inflorescence is somewhat complex; some references describe it as a corymb on the basis of general appearance despite evidence of determinate structure.
Leaves: Opposite, lanceolate, 4"-8" long, wrinkled, with finely toothed margins, and fused at the base so that the stem appears to pass through the leaf.
Blooming: July-September or October. Varies with local conditions.
Habitat: Wet meadows, pond margins, low, open woods.

Comments: The fused leaves are a very unusual feature, not shared even by other closely related plants. The species name perfoliatum means "through the leaf" in latin. This feature suggested to early physicians that the plant would be useful in setting bones, hence the common name. The plant had a number of uses in traditional herbal medicine, including a sweating "cure" for fever. It is actually somewhat toxic, and should be consumed with caution if at all.

Where to find it: There are a few plants near the west end of the pond.