Hymenophyllum fumarioides Bory ex Willd.

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 : 27

15. Hymenophyllum fumarioides Bory ex Willd. (Willdenow 1810: 526), Fig. 14A, B

≡ Mecodium fumarioides (Bory ex Willd.) Copel. ( Copeland 1938: 22). Type:— MAURITIUS. ‘Grands bois à l’île de France’, without date, J. B. G. M. Bory de Saint-Vincent 119, (lectotype B, BW 20 229010!, here designated; isolectotype P, P00547028 !) .

= Trichomanes inaequale Poir. var. ss Poir. ( Poiret 1808: 75). Type:— MADAGASCAR? Without locality, without date, L.-M.A. du Petit-Thouars s.n. (lectotype P, P00483518!, here designated). Note: the Malagasy origin is doubtful (as discussed below).

= Hymenophyllum ricciifolium Bory ex Willd. (Willdenow 1810: 531), as ‘ ricciaefolium ’. Type :— LA REUNION. ‘ Les grands bois à Bourbon’, without date, J.B.G.M. Bory de St.-Vincent 118 (lectotype B, BW 20 236020!, here designated; isolectotype P, P00477837 !).

= Sphaerocionium tenellum (Jacq.) C.Presl ( Presl 1843: 34), based on Adiantum tenellum Jacq. (von Jacquin 1789: 287, pl. 21, fig. 3). ≡ Hymenophyllum tenellum (Jacq.) Kuhn ( Kuhn 1868: 42), nom. illeg., non D.Don ( Don 1825: 12) ≡ Meringium tenellum (Jacq.) Copel. ( Copeland 1938: 42). Type:— LA REUNION. ‘Crescit in insula Borboniae’, without date, without collector (holotype von Jacquin (1789): pl. 21, fig. 3).

Note: Tardieu-Blot (2008) added H. emersum Baker ( Hooker & Baker 1868: 451) as a synonym. But the type of this species (Thwaites s.n., K001090270!) is from Sri Lanka and clearly a distinct species (even if the Mauritian syntype -K000435618!- is clearly a H. fumarioides ), hence we excluded this taxon from the synonym list.

Short description—Epiphytic; long-creeping filiform rhizomes, bearing sparsely distributed roots and reddish-brown trichomes, and widely separated pending fronds; fronds glabrous, with undulated winged, glabrous stipes and rachises, up to 15 cm long, elliptic to ovate, pinnate-pinnatifid to bi-pinnate-pinnatifid, with curled/undulated lamina in the wild; sori numerous, paratactic, usually at the frond apices, bilabiate with a small base and with irregularly toothed, seeming jagged, margins; receptacle slightly exerted at maturity ( Fig. 14B ).

General distribution—Mascarenes, its presence in Madagascar is doubtful.

Current distribution in Mascarenes— La Réunion, Mauritius.

Ecology—Epiphytic on tree-trunks in lowland and montane rainforests (250–1,400 m).

Representative specimens examined— MAURITIUS. Plateau de Mare Longue, October 2010, S. Hennequin et al. 359 (MAU 0011495, P02432423).

— LA RÉUNION. Saint Philippe , May 1957, J. Bosser 12152 ( P01305955 ) ; Forêt de Mare Longue , September 1968, T. Cadet 1633bis ( P01305829 , specimen A,mix with H.hygrometricum (Poir.) Desv. ), T. Cadet 1634 ( P01305852 ) ; Basse Vallée , April 1999, J.- Y. Dubuisson HR-1999-15 ( P) ; Bébour , April 1999, J.- Y. Dubuisson HR-1999-27 ( P) ; Mare Longue , November 2004, F. Rakotondrainibe et al. 6899 ( P00411900 ) .

Note—This species is known in principal floras ( Tardieu-Blot 1951, 2008; Grangaud 2010) as Hymenophyllum tenellum (Jacq.) Kuhn , but Grangaud noted that the name was likely illigitimate and suggested H. ricciifolium Bory ex Willd as the valid name. Hymenophyllum tenellum is a combination based on Adiantum tenellum Jacq. ( Kuhn 1868), and actually firstly named Sphaerocionium tenellum (Jacq.) C.Presl ( Presl 1843), but the name Hymenophyllum tenellum had already been proposed before by Don (1825) to designate a clearly distinct Asiatic species (type: Hamilton & Wallich s.n.; BM001044318). Hymenophyllum tenellum (Jacq.) Kuhn and its homotypic synonyms are therefore illegitimate. The synonym Hymenophyllum ricciifolium described by Willdenow (1810) appears a priori as a good candidate. But as demonstrated by Saïd et al. (2017), H. fumarioides Bory ex Willd. has been used to describe the same species and this name was proposed before H. ricciifolium by the same author. We thus here propose H. fumarioides as the valid name for specimens formerly identified and named H. tenellum . And we can note here that Cadet (1980) had already used H. fumarioides for naming the taxon.

The species is recognized by its small to medium-size elliptic to ovate, pinnate-pinnatifid to bi-pinnate-pinnatifid curled fronds combined with sori with mostly irregularly toothed, seemingly jagged, margins. Except for the closely related H. sibthorpioides (Bory ex Willd.) Mett. ex Kuhn ( Kuhn 1868: 41) which has dwarf flabellate to reniform fronds, the sori of the other Mascarenan Hymenophyllum species always show conspicuously entire, and neither toothed nor jagged, margins.

The species has not been observed by us neither in the Malagasy collections we have studied, nor in the wild in Madagascar. The Malagasy origin of the type of the synonym Trichomanes inaequale Poir. var. ss Poir. thus appears doubtful and is likely erroneous. Some Malagasy collections (e.g., F. Rakotondrainibe et al. 6981, P00411775, or F. Rakotondrainibe 3032, P00067129) have been identified as H. tenellum , but such specimens, even if they seem slightly crisped, have sori with entire margins, and overall and sorus shapes that do not fit with typical H. tenellum . In addition to margin differences, the sori of H. fumarioides are not or only slightly immersed into the lamina, ovate, and usually longer than wide, and with a small base, whereas the sori of Malagasy specimens are clearly immersed into the lamina, (sub)circular and often shorter than wide, with no small base but two basal veinlets. These features suggest a relationship to subgenus Mecodium , and likely to the local species H. capense Schrad. ( Schrader 1818: 919). We therefore propose here that H. fumarioides is endemic to the Mascarenes.

Figures

FIGURE 14. A. Hymenophyllum fumarioides Bory ex. Willd, as epiphyte (La Réunion, ‘Mare Longue’). B. H. fumarioides, detail of curled/crisped segments and sori with toothed margins. C. H. peltatum (Poir.) Desv., as epiphyte (La Réunion, ‘Pitons Mare à Boue’). D. H. peltatum, detail of toothed/serrulate laminar margins. E. H. sibthorpioides (Bory ex Willd.) Mett. ex Kuhn, as epiphytic (La Réunion, ‘Vallée Heureuse’). F. H. sibthorpioides, fertile frond and sori with toothed margins (photographs. A, E: C. Chaussidon; B, F: L. Bauret; C: J.-Y. Dubuisson; D: J.-M. Tamon).