This is the female part of the plant. In this species, the tail touches the female spike, but some cattails have a gap between the two.
Leaves erect and blade-like.
Cattails grow in dense stands. Parts of the plant are edible for about half the year. Thoreau used this little trick to demonstrate how tightly the seeds are packed into the spike. Cattails clone and form dense colonies from creeping rhizomes under the ground. New shoots appear on the runners and grow through the ground in early spring.