Osmunda claytoniana Linnaeus
interrupted fern

sterile frond
fertile pinnae
fertile pinna

Osmunda claytoniana is a large fern with a conspicuously clumped growth form and fronds often approaching 1 meter in length (0.5-1.0). Mature fertile fronds are unique in our flora, with several pairs of medium to dark brown fertile pinnae inserted along the length of a blade otherwise the same as a sterile frond. The "interruption" of the blade by these conspicuously different fertile pinnae is the basis for the common name. Sterile plants of Osmunda claytoniana may be common under forest canopy, but can be recognized by the lack of a small area of wooly hairs on the under (abaxial) surface at the base of the pinnae, that is present on O. cinnamomea.

O. claytoniana ranges from Ontario to Labrador, south to Tennessee and North Carolina. In Wisconsin it is common throughout the state in a variety of upland and lowland forests.

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