Hymenophyllum inaequale (Poir.) Desv.

Dubuisson, Jean-Yves, Pechon, Timothée Le, Bauret, Lucie, Rouhan, Germinal, Reeb, Catherine, Boucheron-Dubuisson, Elodie, Selosse, Marc-André, Chaussidon, Cécile, Dajoz, Isabelle, Pynee, Kersley, Grangaud, Edmond, Robert, Yannis, Tamon, Jean- Maurice & Hennequin, Sabine, 2018, Disentangling the diversity and taxonomy of Hymenophyllaceae (Hymenophyllales, Polypodiidae) in the Mascarene archipelago, with ecological implications, Phytotaxa 375 (1), pp. 1-58 : 37-38

24. Hymenophyllum inaequale (Poir.) Desv. ( Desvaux 1827: 335), Fig. 17B–D

Trichomanes inaequale Poir. ( Poiret 1808: 74, 75). ≡ Mecodium inaequale (Desv.) Copel. ( Copeland 1938: 96). Type:—‘l’île de Madagascar’, without date, L.-M.A du Petit-Thouars s.n. (lectotype P, P00483501!, here designated; paralectotype P, P00483502!, 2 fronds only, annotated ‘C’, bottom right corner).

= Hymenophyllum gracile Bory ex Willd. (Willdenow 1810: 527). ≡ Sphaerocionium gracile (Bory) C.Presl ( Presl 1843: 35). Type:— MAURITIUS. ‘ De l’île de France’, without date, J.B.G.M. Bory de St. -Vincent 120 (lectotype B, BW 20 231010!, here designated; isolectotype P, P00477835 !).

Short description—Epiphytic; long-creeping filiform rhizomes, bearing sparsely distributed roots and 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), rarely wingless, and rachises fully winged, up to 30(–40) cm long, glabrous, quite variable in shape, triangular to lanceolate, or widely ovate, bipinnate-pinnatifid to often tripinnate-pinnatifid; numerous sori, paratactic, bilabiate without a developed base but two lateral veinlets; receptacle included, sometimes slightly exerted ( Fig. 17D ).

Global distribution—Western Indian Ocean, presence in tropical Africa (according to Kornaś 1984) awaits confirmation.

Current distribution in Mascarenes— La Réunion, Mauritius.

Ecology—Epiphytic on tree-trunks from lowland rainforests to high elevations (100–2,400 m).

Representative specimens examined— MAURITIUS. Gaulettes Serrées, May 2007, K. Pynee et al. s.n. ( MAU 0008222 ) ; Alma Hill , October 2012, K. Pynee et al. s.n. ( MAU 0008230 ) ; Tamarind Falls , May 2011, K. Pynee et al. s.n. ( MAU 0008244 ) ; Bar Le Duc , August 2011, K. Pynee et al. s.n. ( MAU 0009261 ) ; Curepipe Point , February 2013, K. Pynee et al. s.n. ( MAU 0011917 ) ; Macabé , October 2010, S. Hennequin et al. 338 ( MAU 0014814 , P02432402 ) .

— LA RÉUNION. Bélouve , April 1956, J. Bosser 9563 ( P01305963 ) ; Mare Longue , April 2016, L. Bauret 187, 186, 190 ( P) ; Vallée Heureuse , April 2016, L. Bauret 197 ( P) ; Ravine Pont Rouge , April 2016, L. Bauret 192 ( P) ; Pandanaie de la Plaine des Palmistes , April 2016, L. Bauret 198 ( P) ; Ravine des Grègues , April 2016, L. Bauret 194 ( P) .

Note— Hymenophyllum inaequale can be easily confused with similar Mecodium species, and especially the specimens often classified under H. polyanthos (Sw.) Sw. ( Swartz 1800: 102). However, molecular phylogenetic results indicate that H. inaequale is distinct from Tanzanian H. kuhnii C.Chr. ( Christensen 1905: 363) and paleotropical H. “polyanthos ” (including H. capense ) and all these species are also distinct from true neotropical H. polyanthos ( Hennequin et al. 2003, 2010). Furthermore, H. inaequale , especially on La Réunion, presents a high level of polymorphism in laminar shape. At low elevations and in shady places, we often observe specimens showing quite long and pending narrowly lanceolate, plane fronds with highly acute to attenuate apices and pinnae often linear and clearly distinct and not overlapping ( Fig. 17B ). By contrast, at high elevations and in sunny places, specimens are smaller, with fronds more widely lanceolate or ovate, often with obtuse to rounded apices and apical pinnae often overlapping, and laminae sometimes slightly curled ( Fig. 17C ). Such differences could suggest the existence of at least two distinct species: H. inaequale and H. kuhnii or H. capense , the latter both potentially present in the region (as discussed by Saïd et al. 2017). However, personal unpublished molecular data and presence of all the intermediate forms in the wild clearly indicate that H. inaequale is the single, large, highly polymorphic Mecodium species currently present in the archipelago.

Genus Polyphlebium Copel. ( Copeland 1938: 55)

Figures

FIGURE 17.A. Hymenophyllum balfourii Baker, holotype (La Réunion, I.B. Balfour s.n., K000435603). B. H. inaequale (Poir.) Desv., as epiphyte, narrowly lanceolate form (La Réunion, ‘Mare Longue’). C. H.inaequale, widely lanceolate to ovate form (La Réunion, ‘Forêt de Bon Accueil, Les Makes’). D. H. inaequale, detail of glabrous segments and sori (photographs. B. L. Bauret; C–D: J.-Y. Dubuisson).