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Osmundastrum C. Presl. Cinnamon Fern.

A monotypic genus, of the Americas and e. Asia. “When the rbcL trees, the fossil and morphological evidences are all taken into account, it can be concluded that the extant Osmunda cinnamomea has no closely related living species in Osmundaceae, and it has evolutionarily very static morphology with no significant modification for more than 200 million years. Thus we can call extant Osmunda cinnamomea a ‘living fossil’ “ (Yatabe, Nishida, & Murakami 1999); Metzgar et al. (2008) confirmed the opinion that cinnamon fern is an outlier and warrants generic status.

ID notes: Sterile plants of Osmundastrum cinnamomeum are sometimes confused with Anchistea virginica, which also has rather coarse, pinnate-pinnatifid leaves and grows in similar wet, acid places. Osmundastrum is coarser (to 2 m tall, vs. to 1 m tall), has cinnamon tufts of tomentum present in the axils of the pinnae (vs. absent), has the rachis greenish and rather fleshy in texture (vs. brown and wiry), and bears fronds clumped or tufted from a massive, woody, ascending rhizome covered with old petiole bases (vs. fronds borne scattered along a thick, horizontal, creeping rhizome). See Claytosmunda for discussion of distinctions from Osmundastrum.

Ref: Arana & Ponce (2015); Kramer & Green (1990); Lellinger (1985); McAvoy (2011); Metzgar et al. (2008); Whetstone & Atkinson (1993) In Flora of North America Editorial Committee (1993b); Yatabe, Nishida, and Murakami (1999); Zhang, Iwatsuki, & Kadokawa in FoC (2013). Show full citations.

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