Key to the Moss Genera of North America

Bryophyte Flora of North America

Key to the Moss Genera of North America North of Mexico

Dale H. Vitt and William R. Buck

Based on a key originally published in Contributions from the University of Michigan Herbarium 18: 43-71. 1992, which holds the copyright.

1. Gametophytes seemingly absent (consisting only of protonemata); sporophytes of asymmetric capsules and papillose setae.	Buxbaumia
1. Gametophytes present (with obvious leaves); sporophytes various.	2
2. Leaf cells arranged in a network of narrow, green cells alternating with large hyaline cells; branches usually in clusters.	Sphagnum
2. Leaf cells of one kind (green), or if of two kinds, branches never in clusters.	3
3. Leaves attached in two rows on opposite sides of the stem (distichous).	4
3. Leaves attached all around the stem (foliate stems sometimes flattened [complanate]).	7
4. Leaves appearing split at the base, consisting of two vaginant laminae which clasp the stem and base of the leaf above (equitant).	Fissidens
4. Leaves with expanded bases, not clasping leaf above.	5
5. Leaves ecostate; protonemata luminous.	Schistostega
5. Leaves unicostate; protonemata not luminous.	6
6. All leaves with a rough (papillose), linear subula.	Distichium
6. Vegetative leaves with a smooth mucro; perichaetial leaves with a smooth subula.	Bryoxiphium
7. Leaves with lamellae or filaments on the adaxial (upper) surface of the costa (excluding propagula).	8
7. Leaves without lamellae or filaments on the adaxial surface of the costa (but propagula sometimes present).	23
8. Leaves with filaments on the adaxial surface of the costa.	9
8. Leaves with lamellae on the adaxial surface of the costa.	10
9. Leaf margins broadly inrolled (and mostly obscuring the filaments).	Aloina
9. Leaf margins reflexed to revolute	Crossidium
10. Leaves bordered with elongate cells.	Atrichum
10. Leaves without elongate, marginal cells.	11
11. Leaves ciliate at upper part of hyaline sheath.	Bartramiopsis
11. Leaves eciliate.	12
12. Upper leaf margins bistratose with paired, multicellular teeth; leaf apices with slender, smooth, caducous awns; restricted to the arctic.	Lyellia
12. Upper leaf margins unistratose with single teeth or entire; leaf apices muticous or with serrate awns.	13
13. Lamellae 2-4; leaves hyaline awned; plants small, less than 5 mm; peristome none or rudimentary and fragile.	Pterygoneurum
13. Lamellae 4-50; leaves mostly not awned; plants mostly larger; peristome of 32 or 64 persistent teeth.	14
14. Lamellae distinctly wavy.	15
14. Lamellae straight.	16
15. Upper leaf margins with border of hyaline, short- rhombic cells.	Psilopilum
15. Upper leaf margins not bordered.	Oligotrichum
16. Leaf laminae with teeth on abaxial (back) surface; calyptrae naked or with a few hairs.	Oligotrichum
16. Leaf laminae smooth at back; calyptrae densely hairy.	17
17. Plants with capsules.	18
17. Plants without capsules.	20
18. Capsules (2-)4(-6)-angled.	Polytrichum
18. Capsules cylindric.	19
19. Capsules without stomates; lumina of apical cells of lamellae not pyriform.	Pogonatum
19. Capsules with stomates; lumina of apical cells of lamellae pyriform.	Polytrichastrum
20. Apical cells of lamellae smooth or with faint cuticular ridges.	21
20. Apical cells of lamellae papillose.	22
21. Plants small, less than 6 mm high; leaves never awned.	Pogonatum
21. Plants larger; leaves with or without awns.	Polytrichum
22. Apical cells of lamellae rounded, quadrate or oblate.	Pogonatum
22. Apical cells elliptic-pyriform.	Polytrichastrum
23. Leaves deeply lobed with lobes linear-terete.	Takakia
23. Leaves never lobed, flattened (although sometimes concave with margins inrolled or recurved).	24
24. Leaves without a costa or costa short and double, double, or single with 2-3 lateral spurs.	25
24. Leaves with a single costa to at least midleaf.	114
25. Although appearing none, costa single and occupying entire leaf area, thus leaf appearing multistratose.	26
25. Costa truly none or double; lamina always unistratose.	27
26. Leaves ligulate; green cells (chlorocysts) three- sided in section.	Octoblepharum
26. Leaves lanceolate; green cells four-sided in section.	Leucobryum
27. Upper leaf cells papillose or prorulose.	28
27. Upper leaf cells smooth (rarely with minute cuticular roughenings).	46
28. Leaf apices hyaline.	29
28. Leaf apices concolorous.	30
29. Leaf cells with a single, unbranched papillae (on each surface); capsules exserted, ribbed; perichaetial leaves entire; restricted to western North America.	Pseudobraunia
29. Leaf cells with 1-2 forked papilla (on each surface); capsules immersed, smooth; perichaetial leaves ciliate; widespread.	Hedwigia
30. Leaf cells pluripapillose.	31
30. Leaf cells unipapillose or prorulose.	33
31. Papillae arranged in rows over the lumina; leaf cells more than 5:1.	Taxithelium
31. Papillae randomly arranged over lumina; leaf cells less than 4:1.	32
32. Leaves obtuse; stems complanate-foliate.	Erpodium
32. Leaves short-acuminate; stems symmetrically foliate.	Braunia
33. Plants 2-3 pinnate, each year forming a flattened frond, the fronds arranged in a stair-step ascending pattern.	Hylocomium
33. Plants simple or 1-pinnate, not forming ascending fronds.	34
34. Leaves plicate.	35
34. Leaves not plicate.	36
35. Costa double and extending to above midleaf; leaves spreading to squarrose.	Rhytidiadelphus
35. Costa short and double; leaves falcate-secund.	Ctenidium
36. Plants reddish-black, occurring tightly attached to rocks.	Andreaea
36. Plants greenish, occurring on various substrates.	37
37. Plants minute, less than 2 mm, acrocarpous.	Ephemerum
37. Plants large, more than 1 cm, pleurocarpous.	38
38. Costa strong and double, extending to near leaf apex.	Callicostella
38. Costa short and double, ending below midleaf.	39
39. Alar cells numerous, oblate to rounded, strongly differentiated and extending up the margins; restricted to Pacific Northwest.	Pterogonium
39. Alar cells few, mostly quadrate, scarcely extending up the margins; widespread.	40
40. Cells at midleaf more than 5:1.	41
40. Cells at midleaf less than 5:1.	43
41. Apical leaf cells much shorter than those at midleaf.	Taxiphyllum
41. Apical leaf cells scarcely differentiated.	42
42. Leaves slenderly acuminate; prorulose at both upper and lower ends of cells.	Chrysohypnum
42. Leaves acute; prorulose only at upper ends of cells.	Leptohymenium
43. Stem and branch leaves differentiated.	Heterocladium
43. Stem and branch leaves similar.	44
44. Leaves broadly ovate, concave, obtuse to obtuse- apiculate.	Myurella
44. Leaves lanceolate to ovate-lanceolate, acute to acuminate.	45
45. Leaves acute, serrulate only above; propagula often in leaf axils; northern in distribution.	Pterigynandrum
45. Leaves acuminate, serrulate throughout; propagula absent; eastern U.S. in distribution.	Schwetschkeopsis
46. Leaves ending in a hyaline awn.	47
46. Leaves concolorous at apex.	48
47. Leaf cells 2:1 or less, oblate-hexagonal throughout; eperistomate.	Erpodium
47. Leaf cells more than 3:1, upper cells short rhomboidal, basal cells quadrate; peristomate.	Venturiella
48. Plants aquatic, occurring submerged at least part of the year; leaves keeled or flat.	Fontinalis
48. Plants sometimes in wet habitats but never occurring submerged; leaves various but never keeled.	49
49. Plants acrocarpous, usually less than 4 cm.	50
49. Plants pleurocarpous, mostly larger.	53
50. Plants occurring on rock.	51
50. Plants occurring on bare soil.	52
51. Plants reddish-black; capsules valvate.	Andreaea
51. Plants greenish-brown; capsules with four peristome teeth.	Tetrodontium
52. Protonemata abundant; capsules ovoid, apiculate; calyptrae campanulate-mitrate, deciduous.	Ephemerum
52. Protonemata sparse; capsules globose; calyptrae very small, persistent.	Micromitrium
53. Costa single with one or sometimes two supplementary costae on each side.	Antitrichia
53. Costa always double, or if single very short and without supplementary costae.	54
54. Costa long and double, extending to or beyond midleaf.	55
54. Costa short and double, usually ending just above leaf base.	59
55. Stems with numerous paraphyllia.	56
55. Stems lacking paraphyllia.	57
56. Stem leaves plicate, decurrent.	Hylocomiastrum
56. Stem leaves not plicate or decurrent.	Loeskeobryum
57. Leaf cells thin-walled, lax, abruptly bordered by elongate cells.	Cyclodictyon
57. Leaf cells firm-walled, not or only gradually bordered.	58
58. Plants forming mats; leaves falcate-secund at least at branch apices; exostome teeth striate, furrowed.	Trachyxiphium
58. Plants tufted; leaves somewhat contorted when dry but not falcate; exostome teeth papillose, not furrowed.	Lepidopilum
59. Leaves obtuse; plants small, rare, restricted to the mountains of southeastern U.S..	60
59. Leaves acute to acuminate, at least apiculate; plants mostly larger, widespread.	61
60. Leaves asymmetric with a basal lobe.	Homaliadelphus
60. Leaves symmetric without lobe.	Bryocrumia
61. Leaf cells lax, hexagonal.	62
61. Leaf cells firm- to thick-walled, rounded to linear.	63
62. Lateral and dorsal leaves differentiated in areolation; stems pinnately branched.	Vesicularia
62. Lateral and dorsal leaves with similar areolation; stems irregularly branched.	Hookeria
63. Leaves slenderly long-decurrent.	Plagiothecium
63. Leaves not at all decurrent to broadly auriculate.	64
64. Plants slender, thread-like; leaves mostly less than 1 mm long.	65
64. Plants larger; leaves more than 1 mm long.	67
65. Branch leaves more than 0.5 mm long.	Homomallium
65. Branch leaves less than 0.5 mm long.	66
66. Costa short and single; leaf cells rounded-elliptic.	Pseudoleskeella
66. Costa none or very short and double; leaf cells rhombic.	Platydictya
67. Leaves falcate-secund.	68
67. Leaves straight.	84
68. Upper leaf cells oblong-rhombic, ca. 3:1.	69
68. Leaf cells more or less linear, more than 6:1.	70
69. Alar cells numerous, oblate, extending up the margins in many rows.	Leucodon
69. Alar cells few, oblong-quadrate, in 1-2 rows along the insertion.	Sematophyllum
70. Plants regularly and closely pinnate, feather-like; fronds flat, erect to ascending, oblong-triangular.	Ptilium
70. Plants irregularly pinnate to unbranched, not feather-like; stems prostrate to loosely ascending.	71
71. Mature branches erect and producing abundant and conspicuous propagula in their upper leaf axils.	Platygyrium
71. Branches not producing propagula in leaf axils.	72
72. Branches curved-secund when dry, erect when moist; alar cells small and quadrate.	Pylaisiella
72. Branches little altered when dry; alar cells various.	73
73. Alar cells when differentiated quadrate, sometimes enlarged but not at all inflated.	74
73. Alar cells quadrate to oblong, inflated.	79
74. Stems with paraphyllia.	Rhytidiopsis
74. Stems without paraphyllia.	75
75. Plants very large (stem leaves 3.5-5.0 mm), stems ascending to erect; leaves plicate.	Rhytidiadelphus
75. Plants smaller (stem leaves less than 3.5 mm), stems prostrate to ascending; leaves various.	76
76. Alar cells none or very few; pale propagula often clustered in leaf axils.	Isopterygiopsis
76. Alar cells distinctly differentiated.	77
77. Plants occurring on wet rocks in mountain streams.	Hygrohypnum
77. Plants in various habitats but not as above.	78
78. Costa to ca. 1/3 the leaf length with the two forks not meeting at the base; plants of Alaska and Yukon.	Gollania
78. Costa mostly shorter, the forks joining at the base; plants widespread.	Hypnum
79. Plants occurring in calcareous fens or marl pools, dark reddish-brown; leaves obtuse.	Scorpidium
79. Plants occurring in other habitats, golden to green; leaves acute to acuminate.	80
80. Plants occurring on wet rocks in mountain streams.	Hygrohypnum
80. Plants in various habitats but not as above.	81
81. Alar cells thick-walled, inflated in several rows; leaf margins strongly serrate.	Heterophyllium
81. Alar cells inflated in 1(-2) rows, or if more, thin- walled; leaf margins entire to serrulate.	82
82. Stems surrounded by enlarged, thin-walled, hyaline cortical cells (hyalodermis); alar cells in large, subdecurrent areas.	Hypnum
82. Stems surrounded by small, thick-walled, concolorous cells; alar cells in 1(-2) rows.	83
83. Plants very shiny; leaves 0.8-1.4 mm long, densely serrulate above; capsules inclined, asymmetric.	Brotherella
83. Plants slightly shiny; leaves 0.5-1.1 mm long, distantly serrulate above; capsule erect, symmetric.	Pylaisiadelpha
84. Stem leaves abruptly contracted to long setaceous point.	85
84. Stem leaves acute, acuminate or apiculate.	86
85. Leaf apices hyaline; alar cells scarcely differentiated.	Iwatsukiella
85. Leaf apices yellow; alar cells inflated and hyaline.	Wijkia
86. Leaves squarrose-recurved when dry, with channeled apices.	87
86. Leaves erect to spreading, or if squarrose only when moist, the apices mostly not channeled.	88
87. Stem leaves greater than 2.5 mm long; alar cells oblong, somewhat inflated, intramarginal.	Rhytidiadelphus
87. Stem leaves less than 2.5 mm long; alar cells subquadrate, not at all inflated, marginal.	Campylium
88. Plants occurring on wet rocks in mountain streams; leaves ovate, concave.	Hygrohypnum
88. Plants in other habitats but not as above; leaves various.	89
89. Stems complanate-foliate.	90
89. Stems symmetrically foliate.	96
90. Alar cells numerous and quadrate; capsules erect.	Entodon
90. Alar cells few, variously shaped; capsules usually inclined.	91
91. Plants occurring on vertical substrates, tree trunks or rocks.	Neckera
91. Plants occurring on horizontal substrates, rarely the extreme bases of trees.	92
92. Leaf margins serrulate throughout.	93
92. Leaf margins entire or serrulate only in upper half.	94
93. Apical leaf cells shorter than those at midleaf.	Taxiphyllum
93. Apical leaf cells undifferentiated.	Herzogiella
94. Rhizoids arising from leaf axils, papillose; leaf margins more or less entire.	Isopterygiopsis
94. Rhizoids arising from below leaf insertion, smooth; leaf margins serrulate above.	95
95. Pseudoparaphyllia filamentous; annuli not differentiated; plants mostly monoicous.	Isopterygium
95. Pseudoparaphyllia absent; annuli differentiated; plants mostly dioicous.	Pseudotaxiphyllum
96. Alar cells inflated.	97
96. Alar cells rectangular to quadrate, not inflated.	101
97. Plants erect; stems with hyalodermis; alar cells hyaline and in auricles.	Calliergonella
97. Plants prostrate; stems without hyalodermis; alar cells yellowish, not in auricles.	98