1	"Dry plant with leaves very strongly crispate; margins serrate to dentate; sporophytes exserted, usually several per perichaetium"	"Ptychomitrium: probably P. gardneri"
1	"Leaves not crispate, or, if so, with the margins entire; plant monosetous"	2
2	"Leaves deeply concave, mostly with cucullate apices; consistently muticous"	3
2	"Leaves without cucullate apices"	4
3	"Leaves broadly ovate-oblong, with unistratose laminae; cells of lamina more than 10 µm broad"	"Grimmia mollis"
3	"Leaves very narrowly oblong-lanceolate with multistratose laminae; cells less than 10 µm broad"	"Grimmia unicolor"
4	"Leaves plicate above the base with the leaf cross-section showing a thickening along the length of the plica"	5
4	"Leaves not plicate or with the plicae inconspicuous at extreme base, often on only one side of leaf"	6
5	"Laminal cells bulging to papillose; capsule exserted; calyptra cucullate and smooth"	"Grimmia caespiticia"
5	"Laminal cells with surface flat to weakly convex in cross-section; capsule immersed; calyptra mitrate to campanulate, plicate"	"Coscinodon cribrosus"
6	"Leaves spirally 3-ranked; leaf apices when dry spirally inflexed"	"Grimmia torquata"
6	"Leaves not strongly ranked; leaf apices when dry outwardly directed or irregularly arranged"	7
7	"Costa abruptly expanded and flattened in the unistratose basal portion of leaf; costa at base about ten cells wide in abaxial view; costa not at all grooved adaxially in distal portion of leaf; basal cells except for a few juxtacostal ones not at all elongate; alar cells numerous, mostly transversely elongate"	"Grimmia laevigata"
7	"Costa not expanded and flattened, variously restricted to an adaxial channel but never so flattened; basal and alar cells not transversely elongate"	8
8	"Cells of basal leaf margins with transverse walls not significantly thicker than lateral walls"	9
8	"Cells of basal leaf margins with transverse walls markedly thicker than lateral, including marginal, walls"	14
9	"Leaf margins recurved, at least near base on one side"	10
9	"Leaf margins plane to erect"	11
10	"Leaves somewhat crispate when dry; lamina unistratose with bistratose streaks and margins; median laminal cells smooth"	"Grimmia incurva"
10	"Leaves not crispate; lamina bistratose throughout; median laminal cells bulging mammillose to papillose"	"Grimmia elatior"
11	"Leaves falcate and somewhat homomallous; lamina bistratose to below leaf middle; leaves muticous"	"Grimmia hamulosa"
11	"Leaves straight or nearly so; lamina unistratose or with streaks of bistratosities near apex; leaves usually with a prominent hyaline awn"	12
12	"Leaves mostly less than 1.5 mm long, distally subulate with the costa filling essentially all of the subula; capsule exserted on an arcuate seta; peristome absent"	"Brachydontium olympicum"
12	"Leaves longer, not so strongly subulate; capsule various but peristome present"	13
13	"Leaves with bistratose margin mostly only one cell wide; leaf cross-section showing hourglass-shaped vertical walls with the cells deeper than wide and with elliptical lumina; calyptra large and mitrate to campanulate, plicate"	"Coscinodon calyptratus"
13	"Leaves mostly with bistratose margin broader; leaf cross-section with vertical walls not hourglass-shaped and with the cells as deep as wide with angular lumina; calyptra cucullate and smooth"	"Grimmia donniana"
14	"Leaves in cross-section with lamina immediately lateral to the costa only one cell layer thick but with the margin 3-6 cells thick; awn poorly developed or absent on most leaves"	"Grimmia serrana"
14	"Leaves and awns not in all respects as above"	15
15	"Leaves, including the perichaetial leaves, without hyaline awns; costa thick and angular or furrowed in cross-section"	16
15	"Leaves with hyaline awns on at least the perichaetial leaves; costa thin, often not bulging on abaxial surface"	18
16	"Costa grooved abaxially and appearing therefore to have a pair of abaxial lamellae; gemmae never present on leaf apices; plant dark greenish-brown"	"Grimmia ramondii"
16	"Costa angular to rounded abaxially; gemmae usually present on leaf apices; plant deep green compared with most other members of the genus"	17
17	"Leaves with longitudinal cuticular ridges, thus appearing papillose; gemmae yellow to green; costa rounded abaxially"	"Grimmia anomala"
17	"Leaves without such ridges; gemmae red-brown; costae angular on abaxial surface in cross-section"	"Grimmia hartmanii"
18	"Costae in cross-section hardly thicker than lamina with the lateral margins poorly demarcated from the leaf lamina"	19
18	"Costae in cross-section at least twice as thick as lamina with the lateral margins well demarcated"	24
19	"Juxtacostal cells of leaf base more than 4:1, irregularly thickened to sinuose on the lateral walls; capsules exserted"	"Grimmia ovalis"
19	"Juxtacostal cells of leaf base less than 4:1, with lateral walls evenly thickened; capsules immersed"	20
20	"Leaf lamina unistratose throughout; hyaline awn on at least some of the leaves extending farther down the costa than down the margins; calyptra campanulate; perichaetial leaves larger than the adjacent vegetative leaves, never reduced to flaccid hyaline structures"	21
20	"Leaf lamina bistratose throughout; hyaline awn arising from truncate apex of green leaf or somewhat decurrent; calyptra cucullate; perichaetial leaves reduced to flaccid and hyaline structures"	22
21	"Leaves deeply concave without a semblance of a keel; hyaline awns mostly more than 1.5 times as long as the green portion of the leaf"	"Jaffueliobryum raui"
21	"Leaves somewhat keeled distally; hyaline awn similar in length to the rest of the leaf"	"Jaffueliobryum wrightii"
22	"Capsule symmetric with the short seta straight and attached centrally to the capsule base"	"Grimmia tergestina"
22	"Capsule asymmetric with the short seta curved and attached to one side of the capsule base"	23
23	"Plant autoicous with the perigonia obvious in leaf axils immediately below the terminal perichaetia"	"Grimmia americana"
23	"Plant dioicous with perigonial plants usually in separate cushions from the perichaetial plants"	"Grimmia poecilostoma"
24	"Leaf margins plane to erect throughout with not even a trace of basal recurvature"	25
24	"Leaf margins recurved on at least one side at least near base"	34
25	"Leaves linear to narrowly linear-lanceolate, mostly with parallel sides; capsule eperistomate, immersed to barely emergent; perichaetial leaves markedly larger and broader than adjacent vegetative leaves"	26
25	"Leaves lanceolate with costa not filling apex; capsule exserted; perichaetial leaves mostly not well differentiated; peristome present or absent"	27
26	"Distal portion of leaf with costa filling more than 1/2 of leaf width; leaf not deeply grooved on adaxial side of costa in the distal portion of leaf"	"Grimmia mariniana"
26	"Distal portion of leaf with costa more narrow; leaf deeply grooved on adaxial side of costa in the distal portion of the leaf"	"Grimmia nevadensis"
27	"Leaves deeply keeled at the base with the broad costa occupying about 1/4 of that base; cells finely papillose; internal basal cells rectangular with sinuose lateral walls"	"Grimmia lesherae"
27	"Leaves, if keeled, with that keeling primarily in their distal 1/2; costa not so broad; leaf cells mostly smooth; internal basal cells various"	28
28	"Leaves deeply concave with the area near the costa seen in cross-section rising almost vertically from insertion on the costa and forming a deep channel"	"Grimmia reflexidens"
28	"Leaves without such a channeled central area along the costa"	29
29	"Leaf unistratose throughout or with a single row of bistratosity at margin; capsules immersed"	30
29	"Leaf limb distal to the region of rectangular basal cells mostly several layers thick; capsules emergent to exserted"	31
30	"Peristome present; leaves concave with cross-section at mid-leaf almost flat"	"Grimmia plagiopodia"
30	"Peristome absent; leaves strongly keeled with cross-section at mid-leaf V-shaped"	"Grimmia anodon"
31	"Median laminal cells bulging on both surfaces as seen in cross-section"	"Grimmia alpestris"
31	"Median laminal cells flat on both surfaces"	32
32	"Costa cross-section showing well-defined abaxial and adaxial epidermises and showing an abaxial stereid band; distal portion of leaf with multicellular, globose gemmae on adaxial surface"	"Grimmia shastae"
32	"Costa cross-section without such epidermises or stereid bands; epiphyllous gemmae not present"	33
33	"Operculum short obliquely-rostrate; capsule exserted; juxtacostal cells of leaf base rectangular, more than 3:1; plants dioicous"	"Grimmia montana"
33	"Operculum apiculate and not oblique; capsule emergent but barely so; juxtacostal cells of leaf base very short rectangular; plants autoicous"	"Grimmia ungeri"
34	"Costa in cross-section three or more cells wide between the insertion of the laminae on the adaxial surface"	35
34	"Costa in cross-section only 2 cells wide on adaxial surface"	38
35	"Juxtacostal cells of leaf base with even thickening of their lateral walls"	"Grimmia lisae"
35	"Juxtacostal cells of leaf base somewhat sinuose or with nodular thickenings on their lateral walls"	36
36	"Costa near its apex with lamina on each side only 1-5 cells wide with the leaf therefore appearing subulate; leaves in distal one-half sharply keeled with cross-section appearing V-shaped"	"Grimmia arcuatifolia"
36	"Leaves lanceolate, not at all subulate; leaves bluntly keeled and U-shaped in cross-section in distal one-half"	37
37	"Hyaline hairpoint terete; seta straight; leaf margins not recurved in distal one-half, usually recurved only on one side"	"Grimmia longirostris"
37	"Hyaline hairpoint flat; seta curved; leaf margins recurved to revolute on both sides, usually above leaf middle"	"Grimmia leibergii"
38	"Leaves bistratose in much of upper leaf, often with bistratosities filling the distal regions"	39
38	"Leaves unistratose except at margin; awn smooth or nearly so"	41
39	"Leaves deeply concave with the area near the costa seen in cross-section rising almost vertically from insertion on the costa and forming a deep channel; capsules exserted"	"Grimmia reflexidens"
39	"Leaves without such a channel central area along the costa; capsules immersed"	40
40	"Leafy stems less than 0.5 mm wide and mostly less than 25 mm long; leaves less than l mm long; plants forming wiry chestnut-brown turfs on seepages at high elevations; capsules systylious"	"Schistidium tenerum"
40	"Plants and leaves larger; plant green to blackish-green primarily growing on median elevation rocks, not in seepages; capsules not systylious"	"Grimmia pilifera"
41	"Leaves lanceolate, broadest near the base"	42
41	"Leaves elliptic to oblong, broadest near the middle, not at all crispate when dry"	43
42	"Leaves somewhat crispate when dry; plant green to blackish-green; median supra-alar cells with sinuose walls; capsules inserted on a cygneous seta, not systylious"	"Grimmia trichophylla"
42	"Leaves not crispate; plant with a reddish blush, especially near leaf bases; median supra-alar cells not sinuose on lateral walls; capsules immersed and systylious"	"Schistidium: various species"
43	"Perigonia located in leaf axils a few leaves below the perichaetium; calyptra mitrate, covering little more than the operculum; peristome teeth mostly entire"	"Grimmia pulvinata"
43	"Perigonia terminal on branch stems; calyptra cucullate; peristome teeth cribrose, often irregularly split"	44
44	"Hyaline awn present only on perichaetial leaves with vegetative leaves bluntly rounded; basal juxtacostal cells with straight lateral walls"	"Grimmia moxleyi"
44	"Hyaline awn present both on perichaetial and vegetative leaves; basal juxtacostal cells with nodulose walls"	"Grimmia orbicularis"