This large fern has fertile leaves that are unusually showy; they become reddish brown at maturity. The sterile leaves are equally attractive. When the fertile leaves are present, Cinnamon Fern is easy to identify. When fertile leaves are absent, it is difficult to distinguish this fern from Osmunda claytoniana (Interrupted Fern). On sterile leaves, the Cinnamon Fern has persistent tufts of hair at the base of its leaflets (on their undersides), whereas the leaflets of Interrupted Fern lack such tufts of hair. The lobes of Cinnamon Fern's leaflets are slightly more pointed than the lobes of Interrupted Fern, although this distinction is not always reliable. Ferns in the Osmunda genus have forked lateral veins on the leaflet undersides (where the lobes occur) of their sterile leaves; these veins have the shape of a tuning fork. Other ferns usually lack such veins. Fossil records indicate that ferns in the Osmundaceae (Royal Fern family) are among the oldest of ferns; today's survivors can be regarded as living fossils.