In its narrow sense (excluding Matteuccia and other taxa), this genus is generally considered monotypic but variable. It is widespread in eastern North America, and there is a distinct variety in East Asia. The plant is typical of swampy woods of various types (including streamheads on uplands), especially on medium acid soils. In Ky. it is remarkably rare to absent in much of the Bluegrass region, although it does occur locally on relatively fertile soils.