Hymenophyllaceae, Mart. (von Martius, 1835

Ahamada H. Saïd, Sabine Hennequin, Germinal Rouhan & Jean-Yves Dubuisson, 2017, Disentangling the diversity and taxonomy of Hymenophyllaceae (Hymenophyllales, Polypodiidae) in the Comoros, European Journal of Taxonomy 313, pp. 1-53 : 32-34

Dichotomous key for Comorian Hymenophyllaceae

An Identification Assisted par Computer (CAI) is available via the Xper platforms (see p. 8). However, in the absence of network and computer facilities, a ‘traditional’ dichotomous key is useful. The present key requires that fertile specimens (with sori) are available. Didymoglossum cuspidatum is unknown in the archipelago; we nervertheless include it in the key because of the possible confusion with D. erosum .

1. Sori with a developed base, usually tubular ..................................................................................... 7

– Sori without a developed tubular base .............................................................................................. 2

2. Fronds pinnate, never flabellate or reniform; sori margins entire ..................................................... 3

– Fronds flabellate to reniform, palmatisect or digitate; sori margins toothed ...................................... ...................................................... Hymenophyllum sibthorpioides (Bory ex Willd.) Mett. ex Kuhn

3. Laminae hairy ................................................................................................................................... 4

– Laminae glabrous .............................................................................................................................. 5

4. Rachises and stipes winged; lamina hairs pedunculated .......... Hymenophyllum hirsutum (L.) Sw.

– Rachises and stipes wingless (rachises winged in ‘dwarf forms’); lamina hairs not pedunculated .................................................................................. Hymenophyllum capillare Desv.

5. Lamina apices attenuate to obtuse or rounded; pinnae often overlapping ........................................ 6

– Lamina apices highly acute to attenuate, never obtuse to rounded; pinnae usually not overlapping (especially the apical-most ones) ...................................... Hymenophyllum inaequale (Poir.) Desv.

6. Fronds up to 10(–15) cm long, and not more dissected than pinnate-pinnatifid ................................ ...................................................................................................... Hymenophyllum capense Schrad.

– Fronds up to 20(–25) cm long, pinnate-pinnatifid to bipinnate-pinnatifid ......................................... .......................................................................................................... Hymenophyllum kuhnii C.Chr.

7. Rhizomes thick and stout,> 1 mm diam., with numerous robust roots; fertile fronds up to 60 cm long ................................................................................................................................................... 8

– Rhizomes filiform and more or less lax, <1 mm diam., rootless or with root-like shoots covered with the same hairs as rhizomes, or with few reduced roots; fertile fronds usually up to 13 cm long ... 10

8. Rhizomes short-creeping or erect, never branched; fronds usually in clumps ................................ 9

– Rhizomes long-creeping, usually branched; widely separated fronds ................................................ ......................................................................... Vandenboschia gigantea (Bory ex Willd.) Pic.Serm.

9. Rhizomes short-creeping; ultimate segments multi-veined, ovate to spatulate and usually toothed ................................................................................................... Trichomanes boivinii Bosch

– Rhizomes erect; ultimate segments uni-veined, linear, not toothed, with a tapered end .................... ............................................................................ Abrodictyum pseudorigidum Bauret & Dubuisson

10. Fronds not peltate .............................................................................................................................11

– Fronds peltate ..................................... Didymoglossum hildebrandtii (Kuhn) Ebihara & Dubuisson

11. Laminae with false veins (but not folds) parallel to true veins; ultimate segments if fronds not entire or lobed with more than one vein .................................................................................................... 12

– Laminae without false veins (or sometimes with folds) parallel to true veins; ultimate segments always univeined ............................................................................................................................. 18

12. Fronds with marginal hairs; sori with brown margins..................................................................... 13

– Fronds glabrous; sori without brown margins ................................................................................. 14

13. Fronds entire, never lobed; a single sorus per fertile frond; marginal hairs stellate (with 3– 4 rays) ........................................................ Didymoglossum lorencei (Tardieu) Ebihara & Dubuisson

– Fronds entire to pinnatifid; often more than one sorus per fertile frond; marginal hairs isolated or cluster of 2–3(–6) hairs ................................. Didymoglossum robinsonii (Hook. ex Baker) Copel.

14. Fronds well stipitate, fertile fronds 1.5–9.0 cm long ..................................................................... 16

– Fronds sessile or subsessile (sometimes stipitate); fertile fronds up to 1.3(–3.0) cm long ............ 15

15. Fronds entire, never lobed, sessile or subsessile; usually one single sorus per frond ......................... ............................................................................ Didymoglossum rotundifolium (Bonap.) J.P.Roux

– Fronds entire to lobed, subsessile to well stipitate; often more than one sorus per frond................... ......................................................................................... Didymoglossum erosum (Willd.) J.P.Roux

16. Each sorus not located at the extremity of a long segment ............................................................. 17

– Each sorus mostly located at the extremity of a long segment ........................................................... ....................................................................... Didymoglossum kirkii (Hook.) Ebihara & Dubuisson

17. Fertile fronds usually ovate to obovate or deltoid with mostly apical sori, rarely exceeding 6 per frond .................................................... Didymoglossum cuspidatum (Willd.) Ebihara & Dubuisson

– Fertile fronds usually lanceolate to oblong with mostly lateral sori, usually numerous, mostly exceeding 6 per frond ........................ Didymoglossum lenormandii (Bosch) Ebihara & Dubuisson

18. Laminae without more or less continuous submarginal false veins; sori lips variable but never triangular.......................................................................................................................................... 19

– Laminae with more or less continuous submarginal false veins; sori lips triangular.......................... ......................................................................................... Crepidomanes bipunctatum (Poir.) Copel.

19. Fertile fronds up to 3.5 cm long ...................................................................................................... 20

– Fertile fronds 3.5–12.0 cm long (rarely longer) .............................................................................. 21

20. Stipes winged, the wings broaden towards the apex ........................................................................... ...................................................................... Crepidomanes trinerve (Baker) Dubuisson & Ebihara

– Stipes wingless .................................................................................................................................... ....................... Crepidomanes minutum (Blume) K.Iwats. var. mascarenensis Pynee & Dubuisson

21. Rhizomes rootless or bearing root-like shoots; sori more or less as long as wide, less than twice longer than wide ................................................... Crepidomanes inopinatum (Pic.Serm.) J.P.Roux

– Roots, if any, few and reduced; sori longer than wide, often twice or more longer than wide ........... ................................................................ Polyphlebium borbonicum (Bosch) Ebihara & Dubuisson