Osmundastrum Cinnamomeum - Classification

Classification

Traditionally, this plant has been classified as Osmunda cinnamomea L.. However, recent genetic and morphological evidence (Metzgar et al. 2008; Jud et al. 2008) clearly demonstrate that the cinnamon fern is a sister species to the entire rest of the living Osmundaceae. Cladistically, it is either necessary then to include all species of the Osmundaceae, including Todea and Leptopteris in the genus Osmunda, or else it is necessary to segregate the genus Osmundastrum. O. cinnamomeum is the sole living species in the genus, although it is possible that some additional fossils should be assigned to Osmundastrum.

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.

Osmundastrum cinnamomeum is considered a living fossil because it has been identified in the geologic record as far back as 75 million years ago.

The Asian and American populations of cinnamon fern are generally considered to be varieties of a single species, but some botanists classify them as separate species.