There are a number of plants with the species name of perfoliatum or perfoliata. This refers to the opposite leaves being joined together at the base making it look like the stem has perforated the leaves. Cup Plant is an extreme example of this to the point where the leaves make a cup which holds water. Birds, particularly goldfinches, have been seen drinking water out of these cups. It’s likely that any number of species of animals make use of this elevated supply of water.
This plant is easy to distinguish from anything else not only by its leaves, but by its stout square stem.