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.
If you cut a leaf or flowering spike, note the spongy nature of these structures. The tubes allow air, and with it oxygen, to diffuse into the roots of the cattail, sustaining the roots and allowing decomposition immediately adjacent to the roots. Because waterlogged soils are often devoid of oxygen, this simple morphology allows the cattail to obtain nutrients and thrive where few other plants can grow.