Member of the marsilea family. This plant is a fern-ally (a close relative of ferns). In ferns the leaves are called fronds. The stem is underground. The plant is often irregularly shaped with fronds sticking up out of the ground in lines that follow the underground stems. The plant's spores are borne along the underground stems and resemble small, round, and hairy pills or peas.

There are a couple of other delicate, green plants that might be confused with American Pillwort. Flowering Quillwort (Lilaea scilloides) tends to be a bit larger and has both underground and aboveground flowers. Quillwort (Isoetes orcuttii) has similar fronds, but they are straight and come from a single point in the soil.

American Pillwort is related to the fern. It grows from spores instead of seeds and does not make flowers. It is most easily observed on the drying mud around and in vernal pools early in the spring.

American Pillwort is a very unusual little plant. Dig one up to show off its little pill-shaped spore packets. Stick it back in the ground and it will be just fine. By producing its spores underground, the American Pillwort pre-plants itself and guarantees that next year's generation will have just the right growing conditions!