Bryol. Univ. 2: 15, plate 6, fig. 5. 1827.
Plants in lax to dense tufts, glaucous to whitish or yellowish. Stems 0.5–10(–16) cm, erect to inclined or procumbent, simple, 2-fid, or with subfloral whorl of branches; pentagonal in cross section, hyalodermis present, epidermis not prorulose; ± tomentose proximally, rhizoids papillose. Leaves in many rows, rarely in 5 distinct rows, erect-spreading or somewhat secund when dry, erect-spreading to spreading when moist, lanceolate to ovate-lanceolate, 1-stratose; base not sheathing; margins plane or revolute, serrulate usually throughout, teeth single or paired; apex acute to acuminate or rarely obtuse; costa subpercurrent to excurrent, abaxial surface smooth or rough; basal laminal cells usually more lax than distal cells; distal cells subquadrate to oblong or linear, prorulose at distal or proximal ends on both surfaces, rarely smooth or with centric papilla, walls thick or seldom thin. Specialized asexual reproduction absent or by small deciduous brood branches in distal leaf axils. Sexual condition dioicous, less frequently autoicous or rarely synoicous; perigonia gemmiform or discoid; perichaetial leaves scarcely distinct from stem leaves. Seta single, usually elongate, straight or flexuose, rarely curved. Capsule erect, horizontal, or inclined, globose to ovoid, furrowed when dry (smooth to irregularly wrinkled in P. cernua), mouth oblique; annulus absent; operculum conic convex, blunt to mammillate or bluntly apiculate; peristome double or rarely absent; exostome teeth dark red to reddish brown, lanceolate, densely and finely papillose, apically free; endostome yellowish to pale brown, segments keeled, cilia well developed or rudimentary. Spores spheric to reniform, densely and usually coarsely papillose.
Nearly worldwide, except Antarctica.
Species ca. 180 (11 in the flora).
Species of Philonotis are recognized by their 1-stratose leaves and the subfloral whorl of branches on fertile plants. While laminal cells are typically prorulose, sterile stems, especially when subject to periodic inundation, may bear leaves with smooth cells. The alar cells are not or slightly differentiated; the perigonial leaves are scarcely or clearly distinct from stem leaves; the perichaetia are terminal or lateral by innovations; the exostome teeth are trabeculate, usually with rounded to ovoid thickenings on the interior surface; the endostome has a well-developed basal membrane and vertically striate papillose segments.
|1||Sexual condition synoicous; setae curved; capsules smooth to irregularly wrinkled when dry; plants small.||Philonotis cernua|
|1||Sexual condition autoicous or dioicous; setae when present straight or flexuose; capsules furrowed when dry; plants small to large||> 2|
|2||Laminal cells with 1 centric papilla.||Philonotis yezoana|
|2||Laminal cells prorulose from one or both ends, or prorulae sometimes obscure or absent||> 3|
|3||Costae 7/8 leaf length or subpercurrent; leaf apices broadly acute or rounded-obtuse; laminal cells obscurely to clearly prorulose at distal ends; plants small.||Philonotis gracillima|
|3||Costae percurrent to long-excurrent; leaf apices acute to acuminate (rarely some apices obtuse and costae subpercurrent, if so laminal cells prorulose at proximal end); plants small to large||> 4|
|4||Laminal cells prorulose at proximal end or sometimes at either end on adaxial side||> 5|
|4||Laminal cells prorulose at distal end throughout or sometimes at both ends on abaxial side||> 7|
|5||Leaves seriate in 5 spiraled rows; costae with entire abaxial surface coarsely prorulose.||Philonotis seriata|
|5||Leaves not or rarely seriate or spiraled; costae with abaxial surface smooth or weakly prorulose distally||> 6|
|6||Plants large; costae 600 µm wide at base; juxtacostal cells at widest part of leaf 48-100 µm; Greenland.||Philonotis calcarea|
|6||Plants small to large; costae 320 µm wide at base; juxtacostal cells at widest part of leaf 24-40 µm; throughout North America.||Philonotis fontana|
|7||Laminal cells elongate, 5-20:1||> 8|
|7||Laminal cells quadrate to rectangular, less than 5:1||> 9|
|8||Leaves narrowly triangular-lanceolate; laminal cells long, narrow, more than 9:1; prorulae pointed, projecting at extreme distal end of cell; sexual condition autoicous.||Philonotis longiseta|
|8||Leaves triangular- to slightly ovate-lanceolate; laminal cells rectangular, less than 9:1; prorulae rounded, near distal ends or sometimes both ends on abaxial side of cells; sexual condition dioicous.||Philonotis marchica|
|9||Prorulae conspicuous, many; leaf margins strongly revolute, sharply serrulate; costae long-excurrent, distal abaxial surface scabrous; Alabama, Florida.||Philonotis sphaerocarpa|
|9||Prorulae not conspicuous, sometimes obscure, few; leaf margins plane to revolute, bluntly serrulate; costae percurrent to short-excurrent, distal abaxial surface rough; e, w United States||> 10|
|10||Leaf marginal teeth single; costae excurrent; Pacific coast, n Rocky Mountains.||Philonotis capillaris|
|10||Leaf marginal teeth usually paired distally; costae percurrent to short- excurrent; se United States.||Philonotis uncinata|