Asplenium and Hymenasplenium species, Newman, 1840

Fischer, Eberhard & Lobin, Wolfram, 2023, Synoptic Revision of Aspleniaceae (Asplenium, Hymenasplenium) of Rwanda, Phytotaxa 608 (1), pp. 1-65 : 5-7

Key to Asplenium and Hymenasplenium species of Rwanda

1. Lamina undivided .......................................................................................................................................................... A. africanum

- Lamina 1-pinnate or more complex ................................................................................................................................................. 2

2. Lamina 1-pinnate with entire pinnae ................................................................................................................................................ 3

- Lamina with at least the lowermost pinnae pinnatifid to 2–3 pinnate ............................................................................................ 29

3. Fronds proliferous ............................................................................................................................................................................ 4

- Fronds not proliferous .................................................................................................................................................................... 11

4. Fronds spaced on rhizome ......................................................................................................................................... A. gemmascens

- Fronds tufted ..................................................................................................................................................................................... 5

5. Rachis lengthened and ending in gemmae looping and rooting to form large colonies .............................................. A. sandersonii

- Gemmae present at base of terminal segment .................................................................................................................................. 6

6. Largest pinnae <2 cm long, only very rarely proliferous ................................................................................................................ 7

- Largest pinnae> 2 cm long, always proliferous ............................................................................................................................... 8

7. Sori solitary; basal pinnae reduced ............................................................................................................................... A. monanthes

- Sori 2–7; basal pinnae not very reduced ........................................................................................................................... A. normale

8. (6.) Frond ending in terminal segment ± similar to lateral pinnae,> 2 cm wide (not yet recorded in Rwanda) ...... A. gemmiferum

- Frond ending in terminal segment <2 cm wide................................................................................................................................ 9

9. Largest pinnae to 6 cm long, asymmetrically ovate to lanceolate ...................................................................................... A. christii

- Largest pinnae to 16 cm long, narrowly lanceolate to lanceolate-attenuate ................................................................................... 10

10. Rhizome scales linear-lanceolate, 18 × 2 mm; pinnae margin incised into bilobed or crenate lobes ............................... A. boltonii

- Rhizome scales ovate, 4–10 × 2.5–4 mm; pinnae margin minutely crenate-serrate .......................................................... A. elliottii

11. (3.) Fronds spaced on a creeping rhizome ...................................................................................................................................... 12

- Fronds tufted, rhizome erect or shortly creeping ............................................................................................................................ 14

12. Pinnae like a curved parallelogram, basiscopic side distinctly curved, only apex and upper side serrate; sori at angle of 30–45° to costa; terrestrial or epilithic .................................................................................................................... Hymenasplenium kenyense

- Pinnae lanceolate, serrate on acroscopic and basiscopic side; sori ± parallel to costa; canopy epiphytes or low epiphytes to terrestrials ....................................................................................................................................................................................... 13

13. Lamina with 19–24 pairs of lateral pinnae, terminal pinna linear-lanceolate, elongate, lobed to slightly pinnatifid; low epiphytes or terrestrials ...................................................................................................................................................................... A. friesiorum

- Lamina with 7–10 (12) pairs of pinnae, terminal pinna lanceolate to ovate with base confluent with highest lateral pinnae, irregularly pinnatifid; canopy epiphytes ............................................................................................................................... A. ramicola sp. nov.

14. (11) Pinnae in 20–50 pairs .............................................................................................................................................................. 15

- Pinnae <20 pairs ............................................................................................................................................................................ 21

15. Pinnae ca. 0.8–2.5 cm long, usually oblong and not exceeding 1.7 cm in length or triangular-trapeziform and then up to 2.5 cm long ................................................................................................................................................................................................. 16

- Middle pinnae much larger, 4–8 cm long, lanceolate-triangular to lanceolate-rhombic ................................................................ 19

16. Sori up to 15 per pinna; pinnae asymmetrically triangular-trapeziform .......................................................................... A. erectum

- Sori 1–7 per pinna; pinnae broadly ovate to oblong or oblong-dimidiate to oblong ..................................................................... 17

17. Pinnae to 8 × 5.5 mm ................................................................................................................ A. trichomanes subsp. quadrivalens

- Pinnae 10–17 × 4–8 mm ................................................................................................................................................................. 18

18. Sori solitary on each pinna; basal pinnae distinctly reduced ........................................................................................ A. monanthes

- Sori 2–7 per pinna; basal pinnae only slightly reduced .................................................................................................... A. normale

19. (15.) Lower pinnae distinctly reduced; rhizome scales 1–2 mm long (rare non-proliferous form of) ......................... A. protensum

- Lower pinnae not or only slightly reduced; rhizome scales 7–11 mm long ................................................................................... 20

20. Basal pinnae not reduced, distinctly incised; lower acroscopic pinnae lobe larger and almost free ........................... A. burundense

- Basal pinnae slightly reduced, slightly incised; lower acroscopic pinnae lobe only free for ⅓ of its length .................... A. smedsii

21. (14.) Pinnae wedge-shaped to narrowly dimidiate-lanceolate, with long-caudate apex ................................................................ 22

- Pinnae of different shape ................................................................................................................................................................ 23

22. Pinnae narrowly dimidiate-lanceolate, inequilateral, 6–7.5 × 0.5–1 cm ............................................................... A. tenuicaudatum

- Pinnae wedge-shaped, up to 9 × 4.8 cm ......................................................................................................................... A. megalura

23. Pinnae lobed or deeply incised; plants of open rock outcrops ................................................................................... A. stuhlmannii

- Pinnae not lobed, but margins denticulate, serrate or crenate; plants of humid habitats in montane forests ................................. 24

24. Pinnae unequally cuneate at base, narrowly lanceolate to falcate or subtrapezoidal ..................................................................... 25

- Pinnae narrowly triangular to oblong at base, shape different ....................................................................................................... 27

25. Pinnae subcoriaceous, subtrapezoidal, in 6–10 pairs, epiphytic or terrestrial..................................................................................26

- Pinnae herbaceous, narrowly lanceolate to falcate, in 8–20 pairs, terrestrial on forest undergrowth and rocks ... A. inaequilaterale

26. Pinnae margins slightly to coarsely crenulate, fronds 60–120 cm long, lamina shiny, sori in 16–27 pairs, terrestrial or lower epiphytic ...................................................................................................................................................... A. markusbeckeri sp. nov.

- Pinnae margins irregularly denticulate, fronds up to 20 cm long, lamina dull, not shiny; sori in 8–11 pairs, canopy epiphyte ......... ..................................................................................................................................................................................... A. cancellatum

27. (24) Pinnae in 12–24(–30) pairs, 4–6.5(–8) cm long; sori 2.5–6 mm long .................................................................................... 28

- Pinnae in 2–10(–12) pairs, (8–) 10–19 cm long; sori 5–19 mm long ....................................................................................... A. ceii

28. Basal pinnae not reduced, distinctly incised; lower acroscopic pinnae lobe larger and almost free ........................... A. burundense

- Basal pinnae slightly reduced, slightly incised; lower acroscopic pinnae lobe only free for ⅓ of its length .................... A. smedsii

29. (2-) Fronds proliferous ................................................................................................................................................................... 30

- Fronds not proliferous .................................................................................................................................................................... 36

30. Gemmae on rachis extension, plant appearing stoloniferous ............................................................................................. A. mannii

- Gemmae just below terminal pinna ................................................................................................................................................ 31

31. Lamina 1-pinnate-pinnatisect ............................................................................................................................... A. uschiae sp. nov.

- Lamina 2-pinnatifid or 3-pinnatisect to 2-pinnatisect–3-pinnatifid ............................................................................................... 32

32. Lamina 2-pinnatifid; lower pinnae distinctly reduced .................................................................................................. A. protensum

- Lamina 3-pinnatisect to 2-pinnatisect–3-pinnatifid; lower pinnae not or slightly reduced ............................................................ 33

33. Pinnae less than 2 cm long, with 3–4 pairs of pinnules, only slightly tapering towards pinna apex; lower acroscopic pinnules bilobed-furcate ............................................................................................................................................................. A. dregeanum

- Pinnae distinctly more than 3 cm long, with at least 7–9 pairs of pinnules, distinctly tapering towards pinna apex; lower acroscopic pinnules flabellate, or pinnate ......................................................................................................................................................... 34

34. Lower acroscopic pinnule not larger than remaining pinnules, flabellate .................................................................. A. rukararense

- Lower acroscopic pinnule larger than remaining pinnules, pinnate ............................................................................................... 35

35. At least the 2–3 adjacent pinnules to the lower acroscopic pinnule pinnate, with usually 3 teeth ................................ A. bugoiense

- Only the basal acroscopic pinnule lobed, adjacent pinnules linear-lanceolate, unlobed or only slightly lobed at apex ... A. preussii

36. (29) Lamina 3–4 pinnate or 4–5-pinnatifid .................................................................................................................................... 37

- Lamina 2-pinnate, 2-pinnatifid, or occasionally up to 3-pinnate ................................................................................................... 38

37. Rhizome scales up to 13 mm; sori cup-shaped, 1–1.5 mm long .................................................................................. A. hypomelas

- Rhizome scales up to 6 mm; sori linear, 1.5–6 mm long .................................................................................................... A. linckii

38. (36) Rhizomes long creeping; fronds well-spaced ......................................................................................................................... 39

- Rhizomes erect or short creeping; fronds tufted or short spaced ................................................................................................... 43

39. Fronds with numerous microscopic unicellular capitate glands ..................................................................................................... 40

- Fronds subglabrous, without capitate glands .................................................................................................................................. 41

40. Rhizomes less than 4 mm in diameter, lamina not viscid, scales lanceolate with narrow base (not yet recorded for Rwanda) ......... .............................................................................................................................................................................. A. actiniopteroides

- Rhizomes more than 4 mm in diameter, lamina viscid and densely glandular, scales triangular with broad base .............. A. majus

41. (39) False veins absent; scales 6.6–9.9 mm long; fronds 50–85 cm long, 3-pinnatisect to 3-pinnatifid; pinnae in 20–25 pairs ........ .......................................................................................................................................................................................... A. volkensii

- False veins present; scales (3.9) 4.5–4.9 mm long, fronds not exceeding 50 cm, usually much shorter (up to 18 cm), lamina 1–2- pinnate to 2-pinnate-pinnatifid; pinnae in 6–13 pairs ..................................................................................................................... 42

42. Rhizome scales dark red-brown, not auriculate at base (not yet recorded in Rwanda) ...................................................... A. goetzei

- Rhizome scales dark-brown to blackish, base auriculate .................................................................................................... A. uhligii

43. (38) Rhizome short-creeping; fronds spaced, 3-pinnatisect; basal pinnae reduced; pinnae deltoid-ovate or deltoid-oblong; pinnules trapezoid-rhombic; terrestrial in forest floor and swamps of montane forests ............................................................ A. mildbraedii

- Rhizome short-erect; fronds usually tufted, 2-pinnatifid or 2-pinnatisect to 3-pinnatifid or 3-pinnatisect to 3-pinnate; basal pinnae hardly reduced; pinnae shape not as above; in various habitats from alpine rocks to montane and dry forests ............................ 44

44. Fronds fleshy; pinnae oblong to narrowly oblong-obtuse; sori near apex of lobes, forming a marginal ‘pocket’ ....... A. theciferum

- Fronds herbaceous to coriaceous; pinnae not as above; sori not in a marginal ‘pocket’, usually longer than wide, linear ........... 45

45. Lamina narrowly oblong to obtriangular or triangular-deltate; terrestrial plants of rock outcrops in alpine habitats or dry forests .. ......................................................................................................................................................................................................... 46

- Lamina narrowly ovate; terrestrial or epiphytic plants in humid forests ........................................................................................ 47

46. Lamina narrowly oblong to obtriangular; rachis and lower side of pinnules with scales; base of petiole not swollen; lithophyte in dry forests, 1400–1650 m ............................................................................................................................................ A. musiraense

- Lamina triangular to deltate; rachis and lower side of pinnules almost without scales; base of petiole swollen; lithophyte in subalpine or alpine habitats above 2500 m .................................................................... A. adiantum-nigrum var. adiantum-nigrum

47. (45) Lamina membranaceous, delicate; pinnae narrowly triangular ......................................................................... A. abyssinicum

- Lamina herbaceous to coriaceous; pinnae unequally rhombic-attenuate ....................................................................................... 48

48. Pinnae oblong-lanceolate, not cuneate at base; pinnules linear; basal pinnules often different in size and shape from neighbouring pinnules ........................................................................................................................................................................................... 49

- Pinnae unequally rhombic, very unequally cuneate at base; pinnules deltoid to narrowly ovate, never linear; basal pinnules not differing in size and shape from neighbouring pinnules ................................................................................................................ 52

49. Fronds abruptly constricted into a caudate apex ( Fig. 1 A, B ); pinnae oblong-lanceolate to narrowly oblong-triangular with segments only slightly diminishing in length upwards, and thus pinnae only barely attenuate in their apical part which is broadly obtuse to subrounded in its outline; lowermost acroscopic segment in the lower and middle pinnae not or scarcely longer than the middle ones and slightly different from them in shape; montane rainforest ......................................................... A. centrafricanum

- Fronds tapering at apex; pinnae narrowly triangular with segments manifestly diminishing in length upwards, and thus pinnae long tapering in their apical part which is long acuminate to narrowly acute in its outline or sometimes barely attenuate (in A. rutifolium ); lowermost acroscopic segment in the lower and often also in the middle pinnae much longer and different in shape (lanceolate to narrowly elliptic, pinnatilobed to pinnatifid) from the middle segments ................................................................ 50

50. Pinnae oblong and obtuse; lowermost acroscopic segment longer (usually exceeding the adjacent segments for ⅓ of their length), usually 4-pinnatifid ( Fig. 1 C ); gallery forest in savanna .............................................................................................. A. rutifolium

- Pinnae long tapering in their apical part which is long acuminate to narrowly acute in its outline; lowermost acroscopic segment longer (usually exceeding the adjacent segments for ½ of their length), usually 6–10 pinnatifid; upper montane forest ............. 51

51. Lowermost acroscopic segment of the pinnae exceeding the adjacent segments, usually 6-pinnatifid; lowermost basiscopic segments similar to adjacent segments and only slightly larger ( Fig. 1 D, E ) ....................................................... A. loxoscaphoides

- Lowermost acroscopic and basiscopic segments of the pinnae sharply distinct in shape and length from adjacent segments, usually 10-pinnatifid ....................................................................................................................................... A. sertularioides ( Fig. 1 F, G )

52. (48) Lamina narrowly to very narrowly oblong; pinnae unequally rhombic, attenuate, very unequally cuneate at base, glabrous on both surfaces; rachis with few scales; epiphyte or lithophyte in forests ........................................................................... A. lividum

- Lamina ovate to ovate-lanceolate; pinnae deltoid to narrowly lanceolate; lower surface of pinnae and rachis ± densely covered with scales; epiphyte or rarely terrestrial in open woodland, along streets and in montane rainforest ............................. A. aethiopicum

Figures

FIGURE 1. Asplenium centrafricanum group, details of pinnae.—A, B. Asplenium centrafricanum.—C. A. rutifolium.—D, E. A. loxoscaphoides.—F, G. A. sertularioides.—Photographs: E.Fischer. A, B. Mt. Muzimu, C. Akagera. O.Ubonabenshi 54. E.Moggi K5; D. Schellenberg Costa. D. Kilimanjaro. P.Ballings. F, G.Gahinga. Scale bar: A. 1 cm; B. 5 cm; C. 1 cm; D–G. 2 cm. Reproduced with permission from BR, African plants – A Photo Guide www.africanplants.senckenberg.de (D. Schellenberg Costa).