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.