Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Genus Description - Petiole stramineous, stout, with 2 bundles at the base, these uniting upwardly into a single trough-shaped bundle; blade pinnate to tripinnate, sparingly scaly, otherwise glabrous or sparsely hairy; veins free, simple or forked, reaching the margin; indusia borne on the anterior side of the vein, often recurved and crossing the vein and thus hooked or horseshoe-shaped, rarely back to back, subentire or toothed, often ciliate; large wood-ferns with thick, creeping to suberect rhizomes and thin, light green, deciduous lvs, the rhizome and often also the petioles with conspicuous, entire, fibrous scales; rhizome in our spp. beset with old swollen, starch-filled petiole-bases. 150+, cosmop.