When the fertile leaflets are conspicuous during the spring, they provide this fern with an unusual appearance almost like it is afflicted with some kind of disease. Later, these leaflets wither away, leaving a gap (or 'interruption') between the upper and the lower leaflets on each fertile leaf. When only infertile leaves are present, they are difficult to distinguish from the infertile leaves of Cinnamon Fern (Osmunda cinnamomea). Generally, the petioles of Cinnamon Fern are more brown-woolly than those of Interrupted Fern, especially later in the year, when the latter fern becomes hairless (or nearly so). The leaflets of Cinnamon Fern have persistent tufts of woolly hair at their bases along the rachis, while the leaflets of Interrupted Fern are usually glabrous at their bases from the summer onward. Instead of restricting its sporangia toward the middle of its fertile leaves, Cinnamon Fern produces reddish brown fertile leaves that are covered entirely by sporangia from top to bottom.
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