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, scaly, with 2 curved bundles at the base; lvs entire; veins pinnate, free, twice forked, ending short of the margin in linear hydathodes; sori linear, paired, one on the anterior branch of a vein, the other on the posterior branch of the next higher vein, the membranous, entire indusia facing each other and overlapping when young; evergreen terrestrial ferns with erect scaly rhizomes and numerous firm, glossy green, elongate, simple lvs. 8, widespread.