Hymenophyllum inaequale (Poir.) Desv.

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 : 26-27

Hymenophyllum inaequale (Poir.) Desv.

Hymenophyllum inaequale (Poir.) Desv., Mémoires de la Société linnéenne de Paris 6 (2): 335 (1827). –

Trichomanes inaequale Poir., Encyclopedie méthodique, Botanique 8: 74 (1808). – Type: ‘l’île de Madagascar’, L.­M.A du Petit­Thouars s.n. (syn-: P00483501!, P00483502!).

Hymenophyllum gracile Bory ex Willd. , Species plantarum: 527 (1810). – Type: ‘Habitat in sylvis insulae Mauritii’, J.B.G.M. Bory de St.­Vincent s.n. (holo-: BW20231010!; iso-: P00477835!).

Sphaerocionium gracile (Bory) C.Presl , Hymenophyllaceae . Eine botanische Abhandlung: 35 (1843).

Mecodium inaequale (Desv.) Copel., The Philippine Journal of Science 67 (1): 96 (1938).

Short description

Epiphytic; long-creeping filiform rhizomes, bearing sparsely distributed roots and long reddish brown trichomes, and widely separated pending fronds; fronds stipitate, with stipes fully winged or winged only in their upper part and the wing usually thin (up to 2–3 cells wide), with rachises fully winged, up to 30(–40) cm long, glabrous, quite variable in shape, triangular to (narrowly) lanceolate, never widely ovate, bipinnate-pinnatifid to tripinnate-pinnatifid, with lamina apices highly acute to attenuate, never obtuse or rounded; pinnae (especially the apical-most ones) usually not overlapping; numerous sori, paratactic, bilabiate without a developed base.

Global distribution

Western Indian Ocean, Tanzania (where it could be confused with H. kuhnii ).

Distribution in Comoros

Anjouan, Grande Comore.

Additional specimens examined

COMOROS: ANJOUAN, s. loc., 1875, J.M.Hildebrandt 1849 (P00139613); s. loc., 1886, L.Humblot 1541 (P00139610, P01471284, P01471285, P01471286, P01471287); s. loc., Jul. 1940, R.Decary 16426 (P00139608); Sommet du Tringi, 12 Nov. 2009, M.Pignal et al. 3724 (P02439798). GRANDE COMORE, s. loc., 1886, L.Humblot 1562 (P00139611), L.Humblot 1607 (P00139612).

Note

Hymenophyllum inaequale displays almost the same lamina division and shape variability as H. kuhnii ( Fig. 5D ; see the note concerning the latter species). However, phylogenetic molecular results indicate that H. inaequale is distinct from Tanzanian H. kuhnii and paleotropical H. ‘ polyanthos ’ ( Hennequin et al. 2003, 2010). Typical H. inaequale specimens display lanceolate to narrowly lanceolate fronds with highly acute to attenuate apices (never obtuse or rounded), and pinnae or segments (especially the most apical ones) usually do not overlap. By contrast, many H. kuhnii specimens display ovate to widely ovate fronds with obtuse to rounded apices and mostly overlapping pinnae or segments, all these features supporting the distinctiveness from H. inaequale . However, many H. kuhnii specimens can also exhibit lanceolate to oblong fronds with attenuate apices and pinnae which do not always clearly overlap. Such equivocal or intermediate forms hinder a clear distinction between both species. Nevertheless, stipes of H. kuhnii are always fully winged with usually a wing of more than 3 cells wide (and observation of such wing usually requires a binocular). In typical H. inaequale , such wing is also observed, all along the stipe or only in its upper part, and it remains thin (up to 2–3 cells wide). Such subtle differences could allow distinguishing specimens exhibiting similar gross frond shape. But despite such subtle features, the morphological distinction between H. inaequale and H. kuhnii and/or all other non-neotropical H. ‘ polyanthos ’ remains difficult, especially in the wild (see Fig. 5 ).

Figures

Fig. 5. Western Indian Ocean Hymenophyllum subg. Mecodium, illustrating morphological resemblance of taxa which are difficult to distinguish (see text). A. Hymenophyllum kuhnii C. Chr. from Comoros, firstly identified as H. polyanthos (Sw.) Sw. (F. Rakotondrainibe et al. 6864, P 00312328). B. Hymenophyllum capense Schrad. from Madagascar, initially identified as H. fumarioides Bory ex Willd. (F. Rakotondrainibe et al. 6121, P 00212664). C. Syntype of Hymenophyllum kuhnii C. Chr. from Tanzania (B 200092782). D. Hymenophyllum inaequale (Poir.) Desv., representative specimen from La Réunion (L. Bauret 190, P).