 Formerly, some authors included the interrupted fern, "Osmunda claytoniana", in the genus or section "Osmundastrum", because of its gross apparent morphological similarities.However, detailed morphology and genetic analysis have proven that the interrupted fern is actually a true "Osmunda".This is borne out by the fact that it is known to hybridize with the American royal fern, "Osmunda spectabilis" to produce "Osmunda × ruggii" in a family in which hybrids are rare, while "Osmundastrum cinnamomeum" has no known hybrids.