This rhizomatous diploid (2n = 84) is widespread in woods on mesic or submesic fertile soils across east-central states. It is the only fern species typical of the submesic eutrophic woodland that formerly covered uplands of the Inner Bluegrass. C. protrusa differs from tenuis and fragilis (sensu stricto) as follows (FNA 2): leaves clustered 1-4 cm behind protruding stem apex (versus clustered at apex); stems pubescent with golden-yellowish hairs (versus glabrous); spores usually 28-34 µm (versus 39-60 µm). Occasional sterile triploids may be expected, especially in hybrids with other species (FNA 2).