[+] Underleaves scarcely wider than the stem, ovate, bifid, the divisions entire, acute; perianth 1-carinate or smooth, except in n. 2; stems creeping.
2. F. Virgínica, Lehm. Stems short, irregularly branching; leaves crowded, ovate, entire, somewhat concave, the lower lobes sometimes expanded into a lanceolate lamina; underleaves round-ovate, bifid, twice the width of the stem; perianth compressed-pyriform, tuberculate, 2–4-carinate dorsally, 4-carinate ventrally.—On bark of trees, rarely on rocks; common.
3. F. Eboracénsis, Lehm. Branches clustered; leaves loose, imbricate on the branches, round-ovate, entire; perianth pyriform, slightly compressed and repand, smooth, obscurely carinate beneath and gibbous toward the apex. (F. saxatilis, Lindenb.)—On trees and rocks; common northward.
4. F. Pennsylvánica, Steph. Stems dichotomous; leaves imbricate, flat, ovate, mucronate or rarely obtuse, entire; lower lobe marginal, large, round-cucullate; underleaves broadly ovate, deeply parted, the divisions long-acuminate; diœcious; antheridial spikes on short lateral branches, elongated; lobes of the involucral leaves acuminate, much narrowed at base, and the large underleaves carinate-concave, deeply parted, their apiculate divisions entire or toothed.—Shaded rocks, Stony Creek, Carbon Co., Penn. (Rau). Known only from the original description.
5. F. saxícola, Aust. Stems numerous, widely branching; leaves orbicular, scarcely oblique, flat; lower lobe near the stem, small, or rarely larger and round-galeate; underleaves scarcely wider than the stem, subovate, bifid; perianth broadly oblong, bowl-shaped with very short mouth, papillose, abruptly broad-carinate beneath, 1–many-nerved each side of the keel, 2-angled.—Sloping dry trap rocks, Closter, N. J. (Austin).
[+][+] Underleaves 2–3 times wider than the stem, round or subquadrate, bifid, the divisions blunt or truncate.
[++] Leaves lax, rather distant; lower lobe mostly expanded, ovate-lanceolate.
6. F. æolòtis, Nees. Procumbent, irregularly branched or subpinnate; leaves semi-vertical, subsquarrose, obliquely cordate, the lower lobe expanded; underleaves ovate, acutely bifid, the upper margin angular-dentate or entire; sporogonium unknown.—On trees and rocks, chiefly in mountain regions.
[++][++] Leaves close-imbricate; lower lobe galeate, seldom expanded except on terminal leaves.
7. F. squarròsa, Nees. Decumbent, pinnately branching, the short fertile branch lateral; leaves subvertical, suborbicular, obtuse, entire; lower lobe obovate-cucullate or galeate, subappressed; underleaves cordate or rounded, sinuate-subdentate, slightly bifid; perianth oblong, triquetrous, convex dorsally, strongly keeled ventrally.—On rocks and trees, N. Y. to Ohio, and southward; rather common.