Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Genus Description - Lvs scattered along the branched, widely creeping rhizome, firm, evergreen, deeply lobed to once pinnate with sessile, broad-based pinnae, the veins free or areolate only along the costae; petiole with 3 vascular bundles below, these uniting distally; sori rotund or elliptic, borne subterminally on the vein-forks. 150+, cosmop.