1	Costa ending well before the apex; leaf tip rounded to cucullate, muticous; lamina uniformly 1-stratose; laminal cells all quadrate.		42 Grimmia mollis
+	Costa reaching apex; leaf tip rounded to acute, muticous or awned; lamina usually with 2-stratose areas towards margins or with 2-stratose ridges; laminal cells oblate, quadrate, rectangular or elongate		(2)
2 (1)	Seta eccentrically attached to capsule base; capsule immersed, smooth, ventricose; stomata 3-4, large, at base of capsule (subg. Gasterogrimmia)		(3)
+	Seta centrally attached to capsule base; capsule immersed to exserted, smooth to plicate, not ventricose; stomata none to many, small, at neck to base of capsule		(6)
3 (2)	Distal leaves concave-keeled; distal lamina 1-stratose or with 2-stratose patches, margins 1- or 2-stratose; annulus absent or reduced to 1-2 rows of small cells; operculum mammillate		(4)
+	Distal leaves concave; distal lamina 2-stratose with 2-stratose margins; annulus prominent; operculum rostrate		(5)
4 (3)	Peristome present, annulus absent; distal lamina 1-stratose, margins 1- or 2- stratose		1 Grimmia plagiopodia
+	Peristome absent, annulus present; distal lamina 1-stratose with 2-stratose patches, margins 2-stratose.		2 Grimmia anodon
5 (3)	Basal laminal cells thick-walled; gonioautoicous; peristome fully developed.		3 Grimmia americana
+	Basal laminal cells thin-walled; dioicous; peristome rudimentary.		4 Grimmia crinitoleucophaea
6 (2)	Leaves merely 1-stratose distally; margins at most narrowly 2-stratose; one or both leaf margins recurved (G. reflexidens plane) (mostly subg. Rhabdogrimmia)		(7)
+	Leaves 2-3-stratose distally or 1-stratose with distal margins widely 2-stratose (G. sessitana and some G. donniana); leaf margins incurved, plane or recurved		(26)
7 (6)	Costa projecting on abaxial side with two wings.		39 Grimmia ramondii
+	Costa on abaxial side smooth or angled		(8)
8 (7)	Leaves muticous, without awns or only distal leaves with very short awn or hyaline tip		(9)
+	At least distal or perichaetial leaves with distinct awns		(13)
9 (8)	Leaves cucullate.		17 Grimmia atrata (in part)
+	Leaves not cucullate		(10)
10 (9)	Leaves squarrose when moist; medial laminal cells oblate to rounded quadrate		34 Grimmia lisae (in part)
+	Leaves erect to patent when moist; medial laminal cells quadrate to short-rectangular		(11)
11 (10)	Basal marginal cells with thickened transverse walls; seta arcuate; globular gemmae occasionally present on leaves.		41 Grimmia trichophylla (in part)
+	Basal marginal cells with thin transverse walls; seta straight or slightly arcuate; gemmae absent		(12)
12 (11)	One leaf margin recurved; medial laminal cells sinuose; seta straight or slightly arcuate		9 Grimmia elongata
+	Leaf margins both recurved; medial laminal cells with nodulose walls; seta straight.		25 Grimmia lesherae
13 (8)	Awns nearly equal to or much longer than lamina, decurrent, seta straight to flexuose		(14)
+	Awns typically shorter than lamina (G. pulvinata can be long); decurrent or not; seta arcuate to cygneous		(15)
14 (13)	Awns 1-2 mm, leaf margins plane, [seta straight]; only known from Maritime provinces in North America.		12 Grimmia reflexidens
+	Awns 2-4 mm, leaf margins both recurved; seta flexuose; endemic to Montana and Idaho.		28 Grimmia brittoniae
15 (13)	Leaves abruptly narrowed to awns, apex rounded; autoicous		(16)
+	Leaves gradually tapering to awns, apex narrowed; dioicous		(18)
16 (15)	Operculum rostrate; basal marginal laminal cells quadrate to short-rectangular		38 Grimmia pulvinata
+	Operculum mammillate to conical; basal marginal laminal cells short- to long-rectangular		(17)
17 (16)	Awns only on perichaetial leaves; basal juxtacostal cells with thin, straight walls; marginal distal lamina 2-stratose; acidic rocks.		35 Grimmia moxleyi
+	Awns on all distal leaves; basal juxtacostal cells with thick, nodulose walls; marginal distal lamina 1-stratose; basic rocks.		37 Grimmia orbicularis
18 (15)	Clusters of gemmae easily visible on abaxial side of leaf lamina or on leaf tips		(19)
+	Clusters of gemmae absent or in obscure clusters in leaf axils		(21)
19 (18)	Multicellalar gemmae on abaxial side of leaf lamina in distal leaves; leaves crisped and contored.		40 Grimmia torquata
+	Cluster of gemmae only on leaf tips; leaves straight		(20)
20 (19)	Leaves with blunt eroded apices; distal cells with pseudo- papillose walls; stem central strand present.		26 Grimmia anomala
+	Leaves with acuminate apices; distal cells with smooth walls; stem central strand absent.		31 Grimmia hartmanii
21 (18)	Leaves narrowly ovate-lanceolate to linear-lanceolate, distinctly incurved or contorted when dry.		32 Grimmia incurva
+	Leaves lanceolate to ovate-lanceolate, straight, appressed, only occasionally somewhat contorted when dry		(22)
22 (21)	Central strand absent; basal juxtacostal leaf cells uniformly elongate to linear, strongly nodulose and thick-walled; mid leaf cells extremely sinuose and very thick-walled; leaf margins both recurved		(23)
+	Central strand present; basal juxtacostal cells short- to long-rectangular, elongate cells absent or few and scattered; mid leaf cells straight to sinuose, thin- to thick-walled; leaf margins one or both recurved		(24)
23 (22)	Costa circular, projecting in transverse section; basal marginal cells thin-walled; distal leaves straight, awns not decurrent.		27 Grimmia attenuata
+	Costa semicircular, not projecting in transverse section; basal marginal cells thick-walled; distal leaves often secund, awns often decurrent		33 Grimmia leibergii
24 (22)	Leaves squarrose when moist; mid leaf cells rounded to oblate, straight.		34 Grimmia lisae (in part)
+	Leaves erect to patent when moist; mid leaf cells rounded-quadrate to short-rectangular, sinuose		(25)
25 (24)	Blackish green tufts; costa angled or bluntly winged in transverse section; awns denticulate, occasionally decurrent; capsule globose, brown.		36 Grimmia muehlenbeckii
+	Yellowish green tufts; costa semicircular in transverse section; awns smooth to slightly denticulate, not decurrent; capsule oblong-ovoid, yellow-green		41 Grimmia trichophylla (in part)
26 (6)	Leaves concave; costa not prominent; margins plane or incurved; dioicous (subg. Litoneuron)		(27)
+	Leaves keeled; costa prominent; margins recurved, plane or incurved; autiocous or dioicous (mostly subg. Guembelia)		(33)
27 (26)	All leaves muticous, straight or falcate		(28)
+	At least distal leaves awned, straight		(29)
28 (27)	Leaves oblong-lanceolate to ligulate, straight, cucullate, obtuse-rounded; basal marginal laminal cells short-rectangular; widely distributed.		18 Grimmia unicolor
+	Leaves oblong-lanceolate, homomallous-falcate, subulate, uncinate; basal marginal laminal cells quadrate to short-rectangular; endemic to Pacific Coast region.		19 Grimmia hamulosa
29 (27)	Leaves oblong-ovate to oblong-lanceolate; basal marginal laminal cells oblate to quadrate; costa broad at base; awn broadly attached and decurrent.		24 Grimmia laevigata
+	Leaves ovate-lanceolate from an ovate base; basal marginal laminal cells quadrate to long-rectangular; costa narrow at base; awn typically narrowly attached and not decurrent		(30)
30 (29)	Costa-like multistratose leaf bands present in transverse section.		23 Grimmia serrana
+	Costa-like multistratose leaf bands absent		(31)
31 (30)	Capsule emergent, gymnostomous, stomata absent, operculum mammilate; basal laminal cells uniformly short-rectangular, straight and thin-walled.		22 Grimmia nevadensis
+	Capsule exserted, peristome fully developed, stomata present, operculum rostrate; basal marginal and juxtacostal laminal cells typically contrasting in length or thickness		(32)
32 (31)	Basal marginal laminal cells quadrate; basal juxtacostal laminal cells quadrate to short-rectangular; seta sigmoid; capsule wrinkled when dry; perichaetial leaves not enlarged; endemic to eastern North America.		20 Grimmia olneyi
+	Basal marginal laminal cells quadrate to long-rectangular; basal juxtacostal laminal cells rectangular to elongate; seta straight; capsule smooth when dry; perichaetial leaves enlarged; widely distributed.		21 Grimmia ovalis
33 (26)	Margins plane or incurved		(34)
+	Margins recurved on one or both sides		(44)
34 (33)	Costa transverse section circular distally; awn hyaline-tipped to short (0.3 mm), decurrent		13 Grimmia teretinervis
+	Costa transverse section semicircular distally; awn short to long, usually prominent, decurrent or not		(35)
35 (34)	Seta arcuate; leaves spirally curved around stem when dry, flagelliform innovations present		30 Grimmia funalis (in part)
+	Seta straight; leaves straight when dry, flagelliform innovations absent		(36)
36 (35)	Gemmae abundant on adaxial distal leaf surface.		43 Grimmia shastae
+	Gemmae absent on leaves		(37)
37 (36)	Distal laminal cells bulging		(38)
+	Distal laminal cells not bulging		(40)
38 (37)	Leaf margins plane; cladautoicous; basal juxtacostal laminal cells rectangular to elongate; distal juxtacostal laminal cells 1-stratose; stomata present.		10 Grimmia sessitana (in part)
+	Leaf margins incurved; dioicous; basal juxtacostal laminal cells quadrate to short-rectangular; distal juxtacostal laminal cells 2-stratose; stomata present or absent		(39)
39 (38)	Stomata absent; leaves not plicate, not cucullate.		6 Grimmia alpestris (in part)
+	Stomata present; leaves weakly to rarely strongly plicate distally, cucullate		11 Grimmia caespiticia
40 (37)	Margins plane throughout; basal marginal laminal cells short- to long-rectangular; stomata present; autoicous		(41)
+	Margins incurved distally; basal marginal laminal cells quadrate to short-rectangular; stomata absent; dioicous		(42)
41 (40)	Distal juxtaxcostal laminal cells 2-stratose, occasionally 1-stratose; basal marginal leaf cells long-rectangular, hyaline; annulus large, of 2 rows of rectangular cells, revoluble; calyptra mitrate.		8 Grimmia donniana
+	Distal juxtacostal laminal cells 1-stratose; basal marginal leaf cells short- to long-rectangular, rarely hyaline; annulus small, of 1 row of quadrate cells, not revoluble; calyptra cucullate.		10 Grimmia sessitana (in part)
42 (40)	Capsule immersed to emergent, wide-mouthed, peristome rudimentary; endemic to California.		7 Grimmia mariniana
+	Capsule exserted, narrow-mouthed, peristome present, fully developed; widespread in western North America		(43)
43 (42)	Basal juxtacostal laminal cells short- to long-rectangular, distinct from quadrate to short-rectangular basal marginal cells; medial laminal cells rounded, thick-walled.		5 Grimmia montana
+	Basal juxtacostal and marginal cells quadrate to short-rectangular, basal areolation relatively uniform; medial laminal cells quadrate to short-rectangular, thin-walled.		6 Grimmia alpestris (in part)
44 (33)	Leaves muticous, cucullate.		17 Grimmia atrata (in part)
+	Leaves awned, not cucullate		(45)
45 (44)	Leaves spirally curved around stem when dry, flagelliform innovations present.		30 Grimmia funalis (in part)
+	Leaves straight when dry, flagelliform innovations absent		(46)
46 (45)	Sporophytes present		(47)
+	Sporophytes absent		(51)
47 (46)	Capsule immersed		(48)
+	Capsule exserted		(49)
48 (47)	Stem central strand present, epidermis thin; leaf margins 2-stratose, not thickened, one margin recurved (rarely both); leaves broadly ovate- lanceolate.		15 Grimmia arizonae (in part)
+	Stem central strand absent, epidermis thick; leaf margins 3(-4) stratose, thicker than juxtacostal lamina, usually both margins recurved; leaves narrowly lanceolate from an ovate base.		16 Grimmia pilifera (in part)
49 (47)	Seta arcuate; dioicous.		29 Grimmia elatior (in part)
+	Seta straight; autoicous		(50)
50 (49)	Annulus small, 1 row of quadrate cells; stomata in 1 row; basal juxtacostal cells straight and thin-walled.		10 Grimmia sessitana (in part)
+	Annulus prominent, 2 rows of rectangular cells; stomata in 2-3 rows; basal juxtacostal cells sinuose and thick walled.		14 Grimmia longirostris (in part)
51 (46)	Basal juxtacostal cells straight, thin-walled; distal juxtacostal lamina 1-stratose, cells often bulging; plants small (less than 1 cm), blackish; moist, alpine habitats.		10 Grimmia sessitana (in part)
+	Basal juxtacostal cells sinuose, thick-walled; distal juxtacostal lamina at least 2-stratose, cells not bulging; plants robust (greater than 1cm), yellow-green to very dark olivaceous; dry, widely distributed		(52)
52 (51)	Leaf margins 2-stratose, not thickened; stem central strand present, epidermis thin		(53)
+	Leaf margins multistratose and thickened; stem central strand absent, epidermis thick		(54)
53 (52)	Autoicous; costa transverse section reniform; leaves sheathing; widely distributed.		14 Grimmia longirostris (in part)
+	Dioicous; costa transverse section semicircular; leaves not sheathing; American Southwest		15 Grimmia arizonae (in part)
54 (52)	Leaves narrowly lanceolate from an ovate base, usually narrowly recurved on both margins; distal lamina without multistratose bands, never papillose.		16 Grimmia pilifera (in part)
+	Leaves broadly lanceolate, broadly recurved on one margin; distal lamina with multistratose bands, occasionally papillose		29 Grimmia elatior (in part)