1	Leaf apices gradually acute, awns present.		9 Orthotrichum diaphanum
+	Leaf apices obtuse, acute, acuminate, or cuspidate, awns absent		(2)
2 (1)	Leaf margins erect-incurved or involute; leaves ovate, ovate-oblong, or ovate-lanceolate; apices obtuse or rounded; gemmae present; sexual condition dioicous; calyptrae papillose, not or obscurely plicate, naked		(3)
+	Leaf margins plane, reflexed, recurved, revolute, or thick; leaves ± lanceolate, linear, ligulate, or oblong; apices obtuse, acute, acuminate, cuspidate, or mucronate; gemmae absent or present; sexual condition autoicous (dioicous in O. lyellii); calyptrae smooth or rarely papillose, plicate, hairy or naked		(4)
3 (2)	Leaf margins involute; distal laminal cell papillae 2 or 3 per cell; peristome absent; Newfoundland.		15 Orthotrichum gymnostomum
+	Leaf margins erect-incurved; distal laminal cell papillae 1 per cell; peristome present; boreal and western regions.		24 Orthotrichum obtusifolium
4 (2)	Leaves crisped-flexuose when dry; capsules oblong-cylindric or elliptic-cylindric when old, exserted or 1/2 emergent; stomata immersed; Pacific Northwest, Alaska		(5)
+	Leaves erect-appressed, erect, flexuose, or spreading when dry; capsules ovate, oblong, cylindric, or globose, immersed to exserted; stomata superficial or immersed; North America		(6)
5 (4)	Plants 8-20 cm; distal laminal cells 7-11 µm; setae (1.5-)2.5-6 mm; capsules exserted to long-exserted, elliptic-cylindric when old; exostome teeth 8, external surface finely papillose, internal surface finely striate; stomata to mid capsule.		7 Orthotrichum consimile
+	Plants to 1.6 cm; distal laminal cells 8-14 µm; setae (0.8-)1-3(-3.5) mm; capsules barely exserted or sometimes 1/2 emergent, oblong-cylindric; exostome teeth 16, rarely connate in 8 pairs, irregularly papillose-reticulate; stomata in mid and distal capsule.		30 Orthotrichum pulchellum
6 (4)	Leaves 3-4 mm; laminal gemmae present.		22 Orthotrichum lyellii (in part)
+	Leaves usually less than 3 mm; laminal gemmae absent or sometimes present		(7)
7 (6)	Stomata superficial; basal laminal cells elongate, walls thick, ± nodose		(8)
+	Stomata immersed; basal laminal cells rectangular, walls thin, not or somewhat nodose		(26)
8 (7)	Endostome segments occasionally rudimentary, usually absent; exostome teeth erect, sometimes reflexed when old and dry (recurved in O. shawii); prostome usually present		(9)
+	Endostome segments well developed, usually present when capsule is old; exostome teeth usually recurved or reflexed; prostome absent		(15)
9 (8)	Distal laminal cells 2-stratose; leaf margins plane; plants dark green to black.		6 Orthotrichum bolanderi
+	Distal laminal cells 1-stratose; leaf margins revolute or recurved; plants light green to olive green		(10)
10 (9)	Peristome rudimentary, appearing absent.		41 Orthotrichum spjutii
+	Peristome present, evident		(11)
11 (10)	Exostome teeth smooth; distal laminal cells smooth; calyptrae naked; prostome large; on seasonally wet rock.		17 Orthotrichum holzingeri
+	Exostome teeth papillose; distal laminal cells papillose; calyptrae usually hairy; prostome small or absent; on dry rock		(12)
12 (11)	Capsules cylindric or rarely oblong, exserted or rarely sometimes emergent		(13)
+	Capsules globose, ovate, ovate-oblong, short-oblong, or cylindric-ovate, immersed to emergent		(14)
13 (12)	Exostome teeth erect; capsules smooth or slightly plicate distally; exothecial cells homogeneous; endostome usually absent in open capsules.		20 Orthotrichum laevigatum
+	Exostome teeth reflexed-recurved; capsules slightly 8-ribbed distally; exothecial cells differentiated to mid capsule; endostome usually present in at least some capsules.		34 Orthotrichum pylaisii (in part)
14 (12)	Exostome teeth erect or sometimes spreading-recurved when old; usually on rock, sometimes trees.		36 Orthotrichum rupestre
+	Exostome teeth recurved; on trees.		37 Orthotrichum shawii
15 (8)	Exostome teeth reflexed, particularly when old (erect to recurved in O. fenestratum); endostome segments usually 8, narrow, usually of 1 row of cells		(16)
+	Exostome teeth recurved or rarely reflexed; endostome segments 8 or 16, thick, of 2 rows of cells		(20)
16 (15)	Capsules usually ovate to ovate-oblong, usually exserted; exostome teeth 16 or 8 splitting to 16		(17)
+	Capsules usually oblong to cylindric, usually emergent to slightly exserted; exostome teeth 8		(18)
17 (16)	Exostome fenestrate, cancellate; St. Paul's Island, Alaska.		13 Orthotrichum fenestratum
+	Exostome not fenestrate or cancellate; Arctic south to California.		34 Orthotrichum pylaisii (in part)
18 (16)	Capsules oblong, to 1/2 emergent; exostome teeth perforate only at apices, not cancellate; endostome segments usually absent when capsules are old and dry; leaf apices gradually acuminate- cuspidate; saxicolous; w United States.		29 Orthotrichum praemorsum
+	Capsules long-cylindric to oblong, 1/2 emergent to exserted, rarely immersed; exostome teeth deeply perforate, cancellate; endostome segments usually present when capsules are old and dry; leaf apices acute; corticolous; n North America. Capsules long-cylindric to cylindric, longer than 1.5 mm, ribbed to 2/3 length, over 1/2 emergent; endostome papillose; w North America.		1 Orthotrichum affine
19	Capsules oblong to oblong-cylindric, to 1.5 mm, ribbed to 1/2 -2/3 length, usually 1/2-2/3 emergent; endostome smooth or finely verrucose; Great Lakes area, ne North America, Alaska.		39 Orthotrichum sordidum
20 (15)	Calyptrae naked or hairs few near tip; endostome segments hyaline, delicate, as wide as exostome teeth; capsules widest at mouth, ovate-oblong; leaves oblong-lanceolate to oblong; apices rounded-obtuse; plants when mature to 1 cm.		12 Orthotrichum exiguum
+	Calyptrae hairy; endostome segments yellowish brown, stout, narrower than exostome teeth; capsules widest mid capsule or cylindric; leaves lanceolate, rarely oblong-lanceolate; apices acute to acuminate; plants when mature larger than 1 cm		(21)
21 (20)	Sexual condition dioicous; exostome teeth acuminate.		22 Orthotrichum lyellii (in part)
+	Sexual condition autoicous; exostome teeth acute or truncate		(22)
22 (21)	Leaf apices slender-acute; exostome teeth truncate, often connate at base; Appalachian Mountains.		18 Orthotrichum keeverae
+	Leaf apices acute or acuminate; exostome teeth acute, separate to base; absent in Appalachian Mountains		(23)
23 (22)	Exostome teeth 16; endostome usually not erose, segments 16; Arizona, New Mexico.		33 Orthotrichum pycnophyllum
+	Exostome teeth 8, or if 16, endostome erose, segments 8 to 16; temperate and boreal regions southward to California and Missouri		(24)
24 (23)	Capsules slightly 8-ribbed to mid capsule.		40 Orthotrichum speciosum
+	Capsules smooth. Capsules cylindric, emergent to sometimes short-exserted; exostome teeth 8; endostome segments 8.		10 Orthotrichum elegans
25	Capsules ovate, immersed; exostome teeth 16; endostome segments 16.		45 Orthotrichum striatum
26 (7)	Leaf apices obtuse; margins irregularly dentate at apex, or if entire, apex cucullate; calyptrae naked, papillose; on base of trees near streams or seasonally wet rock, sometimes submerged; west of Continental Divide		(27)
+	Leaf apices acute, narrowly obtuse, apiculate, cuspidate, or mucronate, occasionally obtuse; margins entire or denticulate at apex, occasionally papillose-crenulate; calyptrae naked or hairy, smooth; on trunks of trees or dry rock faces; California or e North America		(28)
27 (26)	Plants red-brown to black; leaf apices cucullate; margins entire to sometimes irregularly serrulate near apex; distal laminal cells to 20 µm.		11 Orthotrichum euryphyllum
+	Plants dark green to blackish; leaf apices flat; margins usually irregularly dentate at apex; distal laminal cells to 13 µm.		35 Orthotrichum rivulare
28 (26)	Capsules smooth, constricted at mouth by 8 short ribs when dry; exostome absent; California.		3 Orthotrichum anodon
+	Capsules smooth or 8- or 16-ribbed, usually constricted below mouth when dry; exostome present; widespread in North America		(29)
29 (28)	Distal laminal cells 2-stratose or rarely with few 1-stratose areas		(30)
+	Distal laminal cells usually 1-stratose, rarely 2-stratose in streaks or with marginal cells 2- to multistratose		(31)
30 (29)	Stems erect; leaves similar on vegetative and fertile stems; w North America.		16 Orthotrichum hallii (in part)
+	Primary stems creeping, vegetative and fertile stems erect; leaves differentiated on vegetative and fertile stems; California.		19 Orthotrichum kellmanii
31 (29)	Exostome teeth erect, incurved, or spreading, densely papillose, papillose-striate, striate, or reticulate-papillose; capsules 8- or 16-ribbed		(32)
+	Exostome teeth reflexed or sometimes erect or recurved, finely papillose, rarely striate at apices; capsules smooth or 8-ribbed		(39)
32 (31)	Endostome segments 16, filiform, well developed.		47 Orthotrichum underwoodii
+	Endostome segments absent, or 8, short, not well developed		(33)
33 (32)	Capsules exserted, oblong-cylindric to cylindric, usually with 8 long and 8 short ribs; distal laminal cells 1-stratose.		4 Orthotrichum anomalum
+	Capsules immersed or emergent, rarely short-exserted, ovate or oblong, usually with 8 or 16 ± uniform ribs; distal laminal cells 1- or partially 2-stratose		(34)
34 (33)	Capsules 16-ribbed, ovate; leaves ovate-lanceolate to oblong-lanceolate; apices acute or rarely narrowly obtuse; distal laminal cells 1-stratose, rarely 2-stratose in streaks.		8 Orthotrichum cupulatum
+	Capsules 8- or rarely 16-ribbed, oblong or oblong-ovate, rarely ovate; leaves lanceolate, rarely oblong- or ovate-lanceolate; apices obtuse or blunt, rarely acute; distal laminal cells 1- or 2-stratose		(35)
35 (34)	Distal laminal and/or marginal cells 1-7-stratose		(36)
+	Distal laminal cells 1-stratose		(37)
36 (35)	Marginal and distal laminal cells mostly to completely 2-stratose.		16 Orthotrichum hallii (in part)
+	Marginal cells 2-7-stratose; distal laminal cells 1-stratose; occasionally with 2-stratose streaks.		44 Orthotrichum strangulatum
37 (35)	Plants appearing glaucous; distal laminal cell papillae large, conic or 2-fid; w North America.		28 Orthotrichum pellucidum
+	Plants dull; distal laminal cell papillae small, conic; e, c North America		(38)
38 (37)	Leaves narrowly lanceolate; margins revolute; capsules ovate; exostome teeth finely papillose.		21 Orthotrichum lescurii
+	Leaves oblong-lanceolate; margins plane or weakly recurved; capsules oblong; exostome teeth reticulate- papillose.		27 Orthotrichum parvulum
39 (31)	Capsules smooth when dry, wrinkled and slightly 8-plicate when old; exostome teeth 16, erect to recurved; endostome segments usually absent.		32 Orthotrichum pusillum
+	Capsules 8-ribbed when dry; exostome teeth 8, or 8 splitting to 16, reflexed, occasionally erect or revolute; endostome usually present		(40)
40 (39)	Leaf apices cuspidate; margins incurved to form channel at apex; sw United States.		5 Orthotrichum bartramii
+	Leaf apices obtuse, acute, or apiculate, rarely cuspidate; margins not forming channel at apex; widespread in North America		(41)
41 (40)	Stomata to 1/2 covered by subsidiary cells, cells not projecting, inner walls not much thickened; calyptrae usually naked, sometimes hairs few		(42)
+	Stomata 1/2 to completely covered by subsidiary cells, cells projecting, inner walls thickened; calyptrae usually hairy		(44)
42 (41)	Leaf apices acute, narrowly obtuse, or apiculate; leaves oblong-lanceolate to broadly lanceolate; distal laminal cells 9-14 µm.		26 Orthotrichum pallens
+	Leaf apices acute, apiculate, mucronate, or rounded-obtuse; leaves ovate-lanceolate, ovate-oblong, oblong-ligulate, or lanceolate; distal laminal cells 13-20 µm		(43)
43 (42)	Leaves ovate-oblong to oblong-ligulate; apices rounded-obtuse, often mucronate, carinate; w North America.		14 Orthotrichum flowersii
+	Leaves ovate-lanceolate to lanceolate; apices sharply to slenderly acute, usually apiculate, not carinate; North America.		31 Orthotrichum pumilum (in part)
44 (41)	Marginal cells 2- or 3-stratose; on dry granite rock.		38 Orthotrichum shevockii
+	Marginal cells 1-stratose; on trees, mesic rock		(45)
45 (44)	Exostome teeth striate-reticulate distally; calyptra hairs strongly papillose; distal laminal cell papillae large, conic or 2-fid; leaves loosely twisted when dry.		2 Orthotrichum alpestre
+	Exostome teeth papillose; calyptra hairs smooth or papillose by projecting walls; distal laminal cells smooth or papillae low, not 2-fid; leaves stiff, erect-appressed when dry		(46)
46 (45)	Vaginula with hairs present		(47)
+	Vaginula with hairs absent		(48)
47 (46)	Capsule ribs thin, delicate when dry; California.		23 Orthotrichum norrisii
+	Capsule ribs thick, broad when dry; Newfoundland.		43 Orthotrichum stramineum
48 (46)	Leaf apices incurved when dry; capsules cylindric to cylindric-elliptic, not constricted below mouth; stomata in proximal 1/3 of capsule, covered by subsidiary cells; restricted to west coast.		46 Orthotrichum tenellum
+	Leaf apices not incurved when dry; capsules oblong-cylindric or ovate, not to strongly constricted below mouth; stomata mid capsule, covered by subsidiary cells or not; Rocky Mountains and eastward		(49)
49 (48)	Distal laminal cells larger than 14 µm, lumina smooth, rounded; leaf apices apiculate or slender-acute, rarely obtuse; leaves ovate-lanceolate to lanceolate; stomata not or to 1/2 covered by subsidiary cells.		31 Orthotrichum pumilum (in part)
+	Distal laminal cells to 13 µm, lumina irregular due to uneven wall thickenings; leaf apices bluntly acute to obtuse; leaves lanceolate to oblong-lanceolate; stomata 1/2 to completely covered by subsidiary cells		(50)
50 (49)	Capsules not constricted below mouth, ribs thin, delicate; exostome teeth 8 splitting to 16; subsidiary cells projecting vertically over stomata.		25 Orthotrichum ohioense
+	Capsules strongly constricted below mouth, ribs thick, broad; exostome teeth 8; subsidiary cells projecting horizontally over stomata.		42 Orthotrichum stellatum