Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Genus Description - Petiole coarse, ± erect and stem-like, with several vascular bundles that unite distally to form a gutter-shaped bundle; blade ternate- pinnately 2-3 times compound, the ultimate segments pinnatifid but otherwise entire; pinnae opposite or nearly so; pinnules alternate, their segments oblong to linear with revolute margins; veins "free" but connected by a submarginal vascular strand on which the contiguous and confluent linear sori are borne, these protected by the recurved, modified lf-margin and a minute or often nearly obsolete hyaline inner indusial flap of tissue; coarse ferns with widely creeping rhizomes and coriaceous, deciduous lvs, the rhizome and often also the lvs provided with septate hairs. 1–several, by interpretation, cosmop.