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