1. P. pinnàta, L. Stems irregularly pinnate, fastigiate at the ends; leaves scarcely incubous, ovate-oblong, the rounded apex sometimes slightly decurved; lower lobe minute, flat, oblong, obtuse, as long but not half as wide as the flat, entire, ovate-rectangular, scarcely decurrent underleaves. (Madotheca Porella, Nees.)—On rocks and trees subject to inundation; common. (Eu.)
[*][*] Leaves mostly closely imbricate; stems mostly simply pinnate (or bipinnate in n. 2).
2. P. platyphýlla, Lindb. ([Pl. 24.]) Yellowish or fuscous-green; stems irregularly pinnate, often fastigiate at the ends; leaves obliquely ovate, more or less concave at base and the rounded upper margin curved upward aud undulate, mostly entire; lower lobe obliquely ovate, the margin strongly recurved, with an acute tooth at base; underleaves semicircular, with strongly reflexed margins. (Madotheca platyphylla, Dumort.)—On rocks and trees; common eastward. (Eu.)
3. P. Thùja, Lindb. Fuscous-green or blackish, somewhat regularly pinnate; leaves convex, closely appressed, obliquely round-ovate, the rounded apex decurved, more or less denticulate; lower lobe oblong, obtuse, with an acute tooth at base, longer but narrower than the quadrate underleaves, both with strongly recurved sparsely denticulate margins. (Madotheca Thuja, Dumort.)—On rocks and trees; more common westward. (Eu.)
4. P. dentàta, Lindb. Mostly fuscous-green, irregularly pinnate or subdichotomous; leaves more remote on the branches, obliquely round-ovate, the rounded summit slightly decurved, more or less denticulate; lower lobe decurrent, twisted, obliquely ovate, acute, with recurved undulate denticulate margin and a large acute tooth at base; underleaves twice as wide as the lower lobes, quadrate-oval, the undulate reflexed margin dentate, especially near the base. (Madotheca rivularis, Nees.)—Shaded rocks, Yellow Springs, Ohio (Sullivant). (Eu.)
5. P. Sullivántii, Underw. Stems strongly decurved at the ends in drying; leaves suberect, the straight ventral margin strongly involute toward the apex; cells large, punctate-stelliform; perianth broadly keeled beneath, the keel 2-angled. (Madotheca Sullivantii, Aust.)—Alleghany Mts. (Sullivant); rare.
6. PTILÍDIUM, Nees. ([Pl. 24.])
Leaves incubous, complicate-bilobed, each lobe divided and lacerately ciliate; underleaves 4–5-lobed, ciliate. Diœcious. Fruit terminating short branches. Involucral leaves 2–4, 4-cleft; perianth terete, obovate, the mouth connivent, plicate, denticulate. Calyptra pyriform, coriaceous. Capsule ovate. Spores globose. Antheridia in the base of closely imbricated leaves. (Name a diminutive of πτίλον, a feather, from the fringed foliage.)
1. P. ciliàre, Nees. Stems crowded, subpinnate; fringes of the foliage long-setaceous. (Blepharozia ciliaris, Dumort.)—On rotten logs and stumps; common. (Eu.)
7. TRICHOCÓLEA, Dumort. ([Pl. 24.])