1	Blades simple, pinnatifid, or forked (sometimes with free pinnae at base), not pinnate throughout.		(2)
+	Blades pinnate throughout or pinnatifid only in distal 1/3, pinnae undivided to 1–3-divided.		(8)
2 (2)	Blades less than 2–3 mm wide, linear, frequently forking or with 1–3 small, narrow projections. 7. Asplenium septentrionale		(2)
+	Blades more than 10 mm wide, linear-lanceolate to lanceolate, if lobed, segments resembling adnate pinnae.		(3)
3 (3)	Veins anastomosing to form areoles; blades rooting at tip. 4. Asplenium rhizophyllum		(3)
+	Veins free; blades with apical buds or not but not rooting at tip.		(4)
4 (3)	Blades simple, linear to oblanceolate.		(5)
+	Blades pinnatifid, elliptic, lanceolate, to deltate.		(6)
5 (5)	Blades cordate at base; roots not proliferous. 5a. Asplenium scolopendrium var. americanum		(5)
+	Blades tapered at base; roots proliferous. 6. Asplenium serratum		(4)
6 (6)	Petioles 1 cm or less, dull; stem scales 0.6–1 mm wide, sparsely denticulate. 1. Asplenium dalhousiae		(6)
+	Petioles 1–10 cm, lustrous; stem scales less than 0.5 mm wide, entire.		(7)
7 (7)	Petioles dark-pigmented only at base; blade narrowly deltate. 3. Asplenium pinnatifidum		(7)
+	Petioles and proximal midrib darkly pigmented abaxially; blade oblong-lanceolate. 2. Asplenium ebenoides		(1)
8 (1)	Blades 2–4-pinnate, with only largest pinnae divided to all pinnae divided.		(9)
+	Blades 1-pinnate, pinnae undivided (except in some individuals of A. pumilum).		(18)
9 (9)	Blades deltate-ovate, with 2–5 pairs of pinnae; pinnae generally deltate-ovate to obdeltate, rarely lanceolate to narrowly elliptic; color in living plants dull bluish green. 30. Asplenium ruta-muraria		(9)
+	Blades ovate-lanceolate to linear, with 5–20 pairs of pinnae; pinnae linear to oblong; color in living plants shiny green.		(10)
10 (9)	Delicate root proliferations usually present (commonly buried in mossy soil in crevices, but enabling clone formation); damp, shaded limestone; Florida.		(11)
+	Delicate root proliferations absent or rare; mainly rock crevices; plants not in Florida.		(15)
11 (10)	Spores uniform and normal.		(12)
+	Spores of different sizes and shapes, malformed (irregular in size and shape).		(13)
12 (12)	Blades oblong-lanceolate, mostly 2-pinnate; pinnae lanceolate to oblong-lanceolate. 25. Asplenium cristatum		(12)
+	Blades narrowly lanceolate, 2–3-pinnate; pinnae ovate to ovate-deltate. 31. Asplenium verecundum		(11)
13 (13)	Blades linear-lanceolate, s Florida. 23. Asplenium ×biscayneanum		(13)
+	Blades oblong-lanceolate, c Florida.		(14)
14 (14)	Medial pinnae pinnate throughout; pinnules mostly deeply notched apically.		(14)
+	Medial pinnae pinnate only in proximal 1/2; pinnules mostly shallowly notched apically. 29. Asplenium plenum		(10)
15 (15)	Buds at blade, pinna, and pinnule apices minute, scaly, dormant; Arizona. 27. Asplenium exiguum		(15)
+	Buds absent; foothills and mountains in e United States and s Rocky Mountains.		(16)
16 (16)	Petioles all pale green except at base. 28. Asplenium montanum		(16)
+	Petioles dark reddish brown.		(17)
17 (17)	Blades lanceolate to linear-lanceolate, 1–2-pinnate; proximal pinnae often somewhat reduced; e United States foothills and mountains. 24. Asplenium bradleyi		(17)
+	Blades deltate-ovate to deltate-lanceolate, 2–3-pinnate; proximal pinnae usually largest; s Rocky Mountains. 22. Asplenium adiantum-nigrum		(8)
18 (18)	Pinna pairs 1–2(–4); blades ovate-deltate, with fine nonglandular hairs on veins. 17. Asplenium pumilum		(18)
+	Pinna pairs 5–35; blades mainly oblong to lanceolate, usually with glandular hairs or narrow hairlike scales on veins or blades glabrous.		(19)
19 (19)	Pinnae with conspicuous basal auricles overlapping rachis; sori inframedial; leaves ± dimorphic, upright and tall, or spreading and short; plants often terrestrial. 16. Asplenium platyneuron		(19)
+	Pinnae bases not overlapping rachis; sori medial to supramedial; leaves monomorphic; plants mainly on rock (epiphytic in A. auritum).		(20)
20 (19)	Blades mostly 4–9 cm wide, linear-lanceolate to oblong-lanceolate.		(21)
+	Blades mostly less than 3 cm wide, mainly linear.		(22)
21 (21)	Blades linear-lanceolate, to 35 cm; pinna pairs 10–22, base with conspicuous acroscopic auricle; epiphytic on tree trunks. 10. Asplenium auritum		(21)
+	Blades oblong to oblong-lanceolate, to 20 cm; pinna pairs 4–8, base with or without small acroscopic auricle; on mossy limestone. 8. Asplenium abscissum		(20)
22 (22)	Sori 1(–3), mainly confined to basiscopic side of strongly asymmetric pinnae. 14. Asplenium monanthes		(22)
+	Sori 4–10, on both sides of costa of nearly symmetric pinnae.		(23)
23 (23)	Blade apex prolonged into whiplike extension of rachis terminating in bud. 15. Asplenium palmeri		(23)
+	Blade apex not prolonged, terminal bud absent.		(24)
24 (23)	Pinnae ovate, oblong-ovate, to rhombic, mainly 4–7 mm, length 1–2 times width.		(25)
+	Pinnae oblong-lanceolate to oblong, mainly 6–10 mm, length 3–5 times width.		(28)
25 (25)	Rachises dark reddish brown throughout. 19. Asplenium trichomanes		(25)
+	Rachises dark in proximal 1/3–2/3 or only at base.		(26)
26 (26)	Rachises dark in proximal 1/3–2/3; pinna margins entire to shallowly crenate. 9. Asplenium adulterinum		(26)
+	Rachises dark only at base; pinna margins dentate-crenate.		(27)
27 (27)	Pinnae with basiscopic 1/2 much reduced; blades mainly less than 1 cm wide; n North America. 21. Asplenium trichomanes-ramosum		(27)
+	Pinnae nearly symmetric; blades mainly more than 1 cm wide; s Florida. 11. Asplenium trichomanes-dentatum		(24)
28 (28)	Pinna margins deeply lobed, especially acroscopic and distal margins, cut 1/3 or more distance from margin to costa; s California. 20. Asplenium vespertinum		(28)
+	Pinna margins nearly entire or shallowly crenate-dentate; se United States to e Arizona.		(29)
29 (28)	Pinna margins nearly entire; sori supramedial; spores 32; widespread in s United States. 18. Asplenium resiliens 29. Pinna margins ± shallowly crenate-dentate; sori medial to inframedial; spores 32 or 64; local in se United States.		(30)
30 (30)	Pinna margins shallowly crenulate; auricle present at pinna base; veins obscure; spores 32 per sporangium. 13. Asplenium ×heteroresiliens		(30)
+	Pinna margins serrate to crenate; auricle rudimentary or absent at pinna base; veins evident; spores 64 per sporangium. 12. Asplenium heterochroum		(1)