1	Fronds simple or 2- or 3-forked		(2)
+	Fronds pinnatipartite or more divided		(21)
2 (1)	Fronds 2- or 3-forked into linear segments		(3)
+	Fronds simple, not forked		(4)
3 (2)	Average exospore length less than 37 µm; plants sexual diploids: n = 36II or 2n = 72.		1 A. caucasicum
+	Average exospore length more than 37 µm; plants sexual tetraploid: n = 72II or 2n = 144.		2 A. septentrionale
4 (2)	Veins free, rarely connected near margin, never united into a marginal vein		(5)
+	Veins anastomosing, connected near margin, or united into a marginal vein		(13)
5 (4)	Sori double (paired).		8 A. komarovii
+	Sori simple		(6)
6 (5)	Lamina reniform, ca. 1 ?1 cm		(7)
+	Lamina not reniform, larger than ca. 1 ?1 cm		(8)
7 (6)	Average exospore length 35-40 µm; plants diploid: 2n = 72.		67 A. dolomiticum
+	Average exospore length 41-49 µm; plants tetraploid: 2n = 144.		68 A. ruta-muraria
8 (6)	Stipe shiny black; lamina less than 10 cm, apex obtuse, margin black.		3 A. speluncae
+	Stipe not shiny black; lamina more than 10 cm, apex acute to acuminate, margin not black		(9)
9 (8)	Most sori more than 12 mm, at an angle less than 40° to midrib (rachis); lamina margin repand to entire		(10)
+	Most sori less than 12 mm, at an angle of 40°80°to midrib (rachis); lamina margin crenate to sinuate, often notched		(11)
10 (9)	Fronds lanceolate, 6-10 x longer than wide, apex acute-acuminate; midrib raised, semiterete adaxially; sori at angle of 30°40°to rachis.		6 A. holosorum
+	Fronds narrowly lanceolate, 10-25 x longer than wide, apex acuminate-caudate; midrib sulcate adaxially; sori at angle of 15°30°to rachis.		7 A. ensiforme
11 (9)	Frond stalked; stipe 8-16 cm.		32 A. formosae
+	Frond subsessile; stipe 0.5-6 cm		(12)
12 (11)	Frond linear to narrowly lanceolate, up to 2 cm wide or more than 13 x longer than wide.		4 A. scortechinii
+	Frond lanceolate, 2-2.5 cm wide or less than 13 x longer than wide.		5 A. griffithianum
13 (4)	Lamina orbicular or ovate, base cordate		(14)
+	Lamina lanceolate to oblanceolate, base cuneate, rarely cordate		(15)
14 (13)	Rhizome short and erect; fronds clustered; lamina orbicular; most sori double.		9 A. delavayi
+	Rhizome long and creeping; fronds remote; lamina ovate; most sori simple.		9 see Hymenasplenium cardiophyllum (p. 309)
15 (13)	Mature fronds less than 20 cm, herbaceous to subleathery, apex usually flagelliform, proliferous and rooting; veins anastomosing, forming 1 or 2 rows of areoles but not ending in a marginal vein.		16 A. ruprechtii
+	Mature fronds more than 20 cm, subleathery to leathery, apex not proliferous; veins ending in a marginal connecting vein (A. subg. Thamnopteris)		(16)
16 (15)	Frond distinctly spatulate, widest above middle; midrib stramineous to pale brown		(17)
+	Frond lanceolate, widest near middle; midrib pale or grayish brown to brownish black		(18)
17 (16)	Stipe distinct; midrib semiterete abaxially; lamina reduced at base; plants hexaploid.		10 A. humbertii
+	Stipe very short or absent; midrib keeled abaxially; lamina very gradually reduced into a long broadly winged basal part; plants tetraploid.		11 A. antrophyoides
18 (16)	Stipe basal scales subulate to very narrowly triangular-ovate, more than 10 x longer than wide		(19)
+	Stipe basal scales triangular-ovate, less than 10 x longer than wide		(20)
19 (18)	Midrib abaxially flat; sori covering up to 1/2 of their subtending vein; perispore winged.		12 A. nidus
+	Midrib abaxially prominent, obtusely carinate; sori covering more than 1/2 of their subtending vein; perispore echinate.		13 A. oblanceolatum
20 (18)	Stipe basal scales > 15 mm; lamina with many small scales at base; midrib semiterete abaxially.		14 A. antiquum
+	Stipe basal scales < 15 mm; lamina subglabrous at base; midrib obtusely keeled abaxially.		15 A. phyllitidis
21 (1)	Lamina pinnatipartite-pinnatisect		(22)
+	Lamina 1-4-pinnate		(28)
22 (21)	Lamina densely covered with scales abaxially; veins anastomosing; indusia reduced to a rim of a few cells.		22 A. ceterach
+	Lamina (sub)glabrous abaxially; veins free; indusia distinct, not reduced to a rim		(23)
23 (22)	Several pairs of basal pinnae widely separated from more apical ones		(24)
+	Basal pinnae not widely separated from more apical ones (A. subg. Ceterachopsis)		(25)
24 (23)	Rachis green, without scales.		17 A. castaneoviride
+	Rachis dark brown, with dark filiform scales.		39 A. adnatum
25 (23)	Segments acute, adaxially often with submarginal gemmae at acroscopic side of pinnae.		21 A. qiujiangense
+	Segments obtuse, without submarginal gemmae at acroscopic side of pinnae		(26)
26 (25)	Middle segments up to 10 mm wide; mean exospore length < 35 µm.		18 A. dalhousiae
+	Middle segments more than 10 mm wide; mean exospore length > 35 µm		(27)
27 (26)	Plants up to 20 cm; mean exospore length < 50 µm; plants tetraploid.		19 A. paucivenosum
+	Plants more than 20 cm; mean exospore length > 50 µm; plants octoploid.		20 A. magnificum
28 (21)	Rhizome long creeping; lamina 1-pinnate		(29)
+	Rhizome erect or shortly creeping; lamina 1-4-pinnate		(30)
29 (29)	Rhizome less than 0.6 cm in diam., with few scales; venation with several basal basiscopic veins absent.		see Hymenasplenium (p. 308)
+	Rhizome more than 0.6 cm in diam., densely scaly; all basal basiscopic veins present.		37 A. lepturus
30 (28)	Ultimate pinnules or segments linear, with a single vein; sorus reaching frond margin		(31)
+	Ultimate pinnules or segments not linear, with several veins; sorus rarely reaching frond margin		(37)
31 (30)	Stipe and rachis shiny dark brown to black on both sides		(32)
+	Stipe and rachis not shiny dark brown to black on both sides		(33)
32 (31)	Lamina widest at base.		84 A. pulcherrimum
+	Lamina not widest at base.		85 A. cornutissimum
33 (31)	Plants with minute gemmae on costae or costules.		66 A. tenuifolium
+	Plants not gemmiferous		(34)
34 (33)	Lamina bipinnate		(35)
+	Lamina 3-pinnatifid to 3-pinnate		(36)
35 (34)	Rachis apex flagelliform gemmiferous, often rooting and functioning as a runner; pinnae ascending.		86 A. prolongatum
+	Rachis apex not flagelliform; pinnae spreading, attached at right angle to rachis.		87 A. sampsonii
36 (34)	Pinnae less than 10 cm.		89 A. ritoense
+	Pinnae more than 10 cm.		90 A. trigonopterum
37 (30)	Lamina 1-pinnate		(38)
+	Lamina pinnate-pinnatifid to 4-pinnate		(61)
38 (37)	Stipe and rachis shiny, castaneous to dark brown or black		(39)
+	Stipe and rachis dull, not shiny, green, stramineous, or gray-brown		(46)
39 (38)	Rachis adaxially without brown membranous wings or fingerlike papillae		(40)
+	Rachis adaxially with distinct wings or rows of fingerlike papillae		(41)
40 (39)	Lamina less than 2 cm wide; rachis semiterete; pinnae 1-2 x longer than wide.		30 A. kiangsuense
+	Lamina more than 2 cm wide; rachis with deep furrow adaxially; pinnae 2 or more x longer than wide.		31 A. normale
41 (39)	Rachis with brown to yellowish brown wings		(42)
+	Rachis adaxially with 2 rows of fingerlike papillae		(44)
42 (41)	Rachis with 2 adaxial and 1 abaxial wings, often proliferous near apex		24 A. tripteropus
+	Rachis with 2 adaxial wings, abaxial wing absent, never proliferous		(43)
43 (42)	Plants diploid with average exospore length < 31 µm and average guard cell length < 39 µm.		25 A. trichomanes
+	Plants tetraploid with average exospore length > 32 µm and average guard cell length > 40 µm.		26 A. quadrivalens
44 (41)	Rachis gemmiferous at its base; pinnae (slightly) reduced below apex.		27 A. microtum
+	Rachis not gemmiferous; pinnae not reduced near apex		(45)
45 (44)	Rachis papillae closely set and often coalescent at their base; basal pinnae orbicular-ovate.		28 A. humistratum
+	Rachis papillae separated and rarely coalescent at their base; basal pinnae hastate-deltoid.		29 A. glanduliserrulatum
46 (38)	Costa raised and semiterete on adaxial surface of pinna		(47)
+	Costa flat or depressed (grooved) on adaxial surface of pinna		(50)
47 (46)	Frond apex a single pinna, conform with lateral ones.		32 A. formosae
+	Frond apex a pinnatisect or pinnatifid terminal segment different from lateral pinnae		(48)
48 (47)	Frond apex of 1 or 2 basal segments attached to single terminal pinna; indusia not rolling back at maturity; costa with first basiscopic vein lacking and more distal veins simple.		33 A. matsumurae
+	Frondapex pinnatifid and consisting of several confluent segments; indusia rolling back at maturity; costa with all veins present and forking		(49)
49 (48)	Pinnae obtuse, usually less than 5 cm.		88 A. tenerum
+	Pinnae acuminate to caudate, usually larger.		34 A. wrightii
50 (46)	Frond apex similar to one lateral pinna		(51)
+	Frond apex pinnatifid and not similar to a lateral pinna		(54)
51 (50)	Plants less than 10 cm tall		(52)
+	Plants more than 10 cm tall		(53)
52 (51)	Average exospore length 35-40 µm; plants diploid: 2n = 72.		67 A. dolomiticum
+	Average exospore length 41-49 µm; plants tetraploid: 2n = 144.		68 A. ruta-muraria
53 (51)	Stipe and rachis pale yellow-green to gray; veins irregularly anastomosing near margin.		35 A. finlaysonianum
+	Stipe and rachis brown to dark brown; veins free.		36 A. polyodon
54 (50)	Lamina more than 10 cm wide		(55)
+	Lamina less than 10 cm wide		(56)
55 (54)	Frond herbaceous; rhizome creeping; rachis often gemmiferous near apex; spores pale, perispore echinate.		38 A. trapezoideum
+	Frond papery; rhizome erect; rachis not gemmiferous; spores dark brown-black, perispore lophate.		47 A. saxicola
56 (54)	Rachis dark brown to black, with many dark brown to blackish scales with long filiform apex		(57)
+	Rachis gray-stramineous to green, with few narrowly triangular, reddish brown scales without filiform apex		(58)
57 (56)	Frond shorter than 30 cm, less than 3 cm wide; pinnae oblong, obtuse.		40 A. asterolepis
+	Fronds longer than 30 cm, more than 3 cm wide; pinnae narrowly ovate, acute		41 A. crinicaule
58 (56)	Lamina less than 1.5 cm wide; stipe and rachis green, never gemmiferous.		23 A. viride
+	Lamina more than 1.5 cm wide; stipe dull grayish brown, rachis green in apical part and occasionally gemmiferous		(59)
59 (58)	Gemmae on adaxial surface near pinna apex; scales costate with dark brown central zone and pale hyaline margin; perispore cristate-alate (with narrow crests on thin wings).		44 A. gueinzianum
+	Gemmae on rachis or close to rachis on pinna stalk; scales not costate; perispore costate (with rounded crest on broad ridges)		(60)
60 (59)	Plants tetraploid: 2n = 144; average exospore length less than 36µm.		42 A. indicum
+	Plants octoploid: 2n = 288; average exospore length more than 36µm.		43 A. yoshinagae
61 (37)	Stipe entirely shiny dark brown to black.		83 A. coenobiale
+	Stipe not entirely shiny dark brown to black		(62)
62 (61)	Stipe dark gray to dark brown		(63)
+	Stipe green, abaxially at base and higher up often castaneous to black		(82)
63 (62)	Fronds pinnate-pinnatifid to almost 2-pinnate		(64)
+	Fronds more divided, up to 4-pinnatifid		(70)
64 (63)	Gemmae present		(65)
+	Gemmae absent		(66)
65 (64)	Bud on adaxial surface of pinnae.		44 A. gueinzianum
+	Bud on adaxial surface of rachis below apex.		50 A. cuneatiforme
66 (64)	Rachis densely scaly		(67)
+	Rachis not densely scaly		(68)
67 (66)	Fronds widest near base; stipe more than 5 cm; scales with filiform apical tail.		45 A. aethiopicum
+	Fronds widest near middle; stipe less than 5 cm; scales without filiform apical tail.		51 A. rockii
68 (66)	Plants less than 20 cm tall, usually less than 10 pinnae pairs.		48 A. oldhamii
+	Plants more than 20 cm tall, usually more than 10 pinnae pairs		(69)
69 (68)	Fronds herbaceous; pinna stalk less than 4 mm.		46 A. pseudopraemorsum
+	Fronds leathery; pinna stalk more than 4 mm.		47 A. saxicola
70 (63)	Fronds 3-pinnate or 4-pinnatifid		(71)
+	Fronds 2-pinnate to 3-pinnatifid		(75)
71 (70)	Plants less than 50 cm		(72)
+	Plants more than 50 cm		(73)
72 (71)	Ultimate soriferous segment cuneiform, with several veins and sori.		56 A. wilfordii
+	Ultimate soriferous segment linear with 1 vein and 1 sorus.		89 A. ritoense
73 (71)	Fronds herbaceous; indusia elliptic, ca. 4 mm; indusium margin with glandular hairs.		55 A. bullatum
+	Fronds papery to subleathery; indusia linear, most than 4 mm; indusium margin without glandular hairs		(74)
74 (73)	Pinnules broadly ovate, less than 2 x longer than wide.		57 A. sublaserpitiifolium
+	Pinnules triangular-ovate, more than 2 x longer than wide.		58 A. pseudolaserpitiifolium
75 (70)	Gemmae present on rachis		(76)
+	Gemmae absent		(77)
76 (75)	Pinnae with more than 3 pairs of free pinnules.		49 A. affine
+	Pinnae with less than 3 pairs of free pinnules.		50 A. cuneatiforme
77 (75)	Stipe less than 5 cm; rachis densely scaly.		51 A. rockii
+	Stipe more than 5 cm; rachis not densely scaly		(78)
78 (77)	Largest pinnae with less than 3 pairs of free pinnules, most decurrent on costa		(79)
+	Largest pinnae with more than 3 pairs of free pinnules		(80)
79 (78)	Sori more than 5 mm.		47 A. saxicola
+	Sori less than 5 mm.		52 A. austrochinense
80 (78)	Plants less than 50 cm tall.		53 A. hainanense
+	Plants more than 50 cm tall		(81)
81 (80)	More than 5 free pinnules per pinna; veins close together and almost parallel; free margin of indusium glabrous.		54 A. subspathulinum
+	Less than 5 free pinnules per pinna; venation different; free margin of indusium with glandular hairs.		55 A. bullatum
82 (62)	Fronds lanceolate, reduced at base		(83)
+	Fronds ovate-triangular, not reduced or not much reduced at base		(87)
83 (82)	Pinnae with minute gemma or plantlet at apex		(84)
+	Pinnae not gemmiferous at apex		(85)
84 (83)	Average exospore length less than 29 µm; plants diploid: 2n = 72.		59 A. lushanense
+	Average exospore length more than 29 µm; plants tetraploid: 2n = 144		60 A. exiguum
85 (83)	Fronds thinly herbaceous; stipe and rachis with thin, green lateral wings		61 A. incisum
+	Fronds firmly herbaceous; stipe and rachis without thin, green wings		(86)
86 (85)	Marginal teeth usually slender, obtuse to subacute.		62 A. nesii
+	Marginal teeth short, subacute to mucronate.		A. fontanum
87 (82)	Small gemmae present on pinnae stalk, costa, costule, or rachis tip		(88)
+	Gemmae absent		(90)
88 (87)	Pinnae usually with more than 3 pairs of free pinnules; gemmae on costa or costule.		66 A. tenuifolium
+	Pinnae with less than 3 pairs of free pinnules; gemmae on pinnae stalk or on flagelliform apex		(89)
89 (88)	Lamina triangular, without extended gemmiferous rachis.		64 A. capillipes
+	Lamina oblong-linear with flagelliform gemmiferous apex.		65 A. fugax
90 (87)	Fronds deltoid to broadly triangular		(91)
+	Fronds triangular to ovate; indusial margin not fimbriate		(93)
91 (90)	Margin of indusium not fimbriate.		69 A. interjectum
+	Margin of indusium fimbriate (with long uniseriate hairs)		(92)
92 (91)	Average exospore length 35-40 µm; plants diploid: 2n = 72.		67 A. dolomiticum
+	Average exospore length 41-49 µm; plants tetraploid: 2n = 144.		68 A. ruta-muraria
93 (90)	Stipe green or only brown at very base; rachis entirely green		(94)
+	Stipe and often base of rachis brown on abaxial side		(95)
94 (93)	Fronds thinly herbaceous; average exospore length less than 32 µm; plants diploid: 2n = 72.		81 A. sarelii
+	Fronds firmly herbaceous to subleathery; average exospore length more than 32 µm; plants tetraploid: 2n = 144.		82 A. pekinense
95 (93)	Fronds 3-pinnate at base; pinnae with more than one free acroscopic pinnule		(96)
+	Fronds 2-pinnate at base; pinnae with 1 free acroscopic pinnule		(99)
96 (95)	Plants diploid; average exospore length less than 32 ?.		70 A. tenuicaule
+	Plants polyploid; average exospore length more than 32 ?		(97)
97 (96)	Lamina triangular; stipe base swollen.		79 A. adiantum-nigrum
+	Lamina narrowly triangular to ovate; stipe base not swollen		(98)
98 (97)	Pinna stalk wiry; perispore with many wide pori (reticulate) and almost no ridges.		76 A. kansuense
+	Pinna stalk not wiry; perispore with ridges and few minute pori (cristate).		80 A. anogrammoides
99 (95)	Plants diploid; average exospore length less than 32 ?		(100)
+	Plants polyploid; average exospore length more than 32 ?		(101)
100 (99)	Pinna stalk wiry; marginal teeth broad, mucronate; average exospore length 29-32 ?; perispore reticulate or cristate.		70 A. tenuicaule
+	Pinna stalk not wiry; marginal teeth slender, acute; average exospore length 24-27 ?; perispore alate.		71 A. semivarians
101 (99)	Lamina triangular, widest at base; largest pinnae broadly ovate-deltoid		(102)
+	Lamina ovate, widest just above base; largest pinnae ovate to narrowly triangular		(103)
102 (101)	Plants hexaploid; average exospore length 38-42 ?.		72 A. aitchisonii
+	Plants tetraploid; average exospore length 33-36 ?.		73 A. neovarians
103 (101)	Lamina thin, membranous; largest pinnae triangular to narrowly triangular.		74 A. mae
+	Lamina more firm, herbaceous; largest pinnae ovate to triangular		(104)
104 (103)	Lamina acuminate to shortly caudate; scales with inner part of cell walls warty.		75 A. kukkonenii
+	Lamina not shortly caudate; scales with inner part of cell walls smooth		(105)
105 (104)	Lamina firmly herbaceous to subleathery; basal pinnae deltoid to flabellate.		78 A. altajense
+	Lamina herbaceous; basal pinnae oval-triangular		(106)
106 (105)	Pinna stalk wiry; perispore with many wide pori (reticulate) and almost no ridges.		76 A. kansuense
+	Pinna stalk not wiry; perispore with ridges and few minute pori (cristate).		77 A. varians