Hymenophyllum hygrometricum (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 : 35

22. Hymenophyllum hygrometricum (Poir.) Desv. ( Desvaux 1827: 333), Fig. 16D, E

Trichomanes hygrometricum Poir. ( Poiret 1808: 79). ≡ Sphaerocionium hygrometricum (Poir.) Copel. ( Copeland 1938: 31). Type:— ‘Habitat in Madagascaria’, without date, L.-M.A. du Petit-Thouars s.n. (lectotype P, P00483511!, here designated; isolectotype P, P00483512!). Note: the species would be absent in Madagascar and endemic to the Mascarenes, the locality indicated by Poiret in his protologue and indeed corresponding to the P00483512 specimen would be therefore erroneous.

= Hymenophyllum elasticum Bory ex Willd. (Willdenow 1810: 520). ≡ Sphaerocionium elasticum (Willd.) C.Presl ( Presl 1843: 34, t. 4, fig. 13). Type:—‘A Bourbon et l’île de France’, without date, J.B.G.M. Bory de St. -Vincent s.n. (lectotype B, BW 20 244010!, here designated; isolectotype P, P00477833 !).

= Hymenophyllum flavo-aureum Bory (Bory 1834: 84). ≡ Hymenophyllum hygrometricum (Poir.) Desv. var. flavo-aurea (Bory) Mett. ex Kuhn ( Kuhn 1868: 40). Type:—‘Mascareigne’, without date, C. Bélanger s.n. (not located).

Short description—Epiphytic; long-creeping thin rhizomes, bearing sparsely distributed roots and very abundant long reddish-brown trichomes, and widely separated pending fronds; fronds with wingless stipes and rachises narrowly winged at their upper part, up to 30 cm long, sometimes longer, deltoid to widely lanceolate, bi-pinnate-pinnatifid to tri-pinnate-pinnatifid, densely hairy with reddish-brown, stellate, non-pedonculated trichomes on rachises, veins and margins; numerous sori, paratactic, bilabiate without a developed base nor lateral veinlets, and with hairy margins; receptacle short and included.

Global distribution—Mascarenes, presence in Madagascar doubtful, presence in Seychelles awaits confirmation.

Current distribution in Mascarenes— La Réunion, Mauritius (rare on the island).

Ecology—Epiphytic on tree-trunks in lowland and montane rainforests (50–1,700 m).

Representative specimens examined— MAURITIUS. Brise Fer, December 2012, K. Pynee et al. s.n. ( MAU 0009343 ) ; Mt Cocotte , March 2011, K. Pynee et al. s.n. ( MAU 0019005 ) ; Mt Cocotte , March 2008, K. Pynee et al. s.n. ( MAU) .

— LA RÉUNION. Ste Agathe , July 1875, M. G. de L’Isle 375 ( P01330237 ) ; Bébour , April 1956, J. Bosser 9565 ( P01330245 ) ; Tévelave , February 1962, T. Cadet 13bis ( P01330241 ) ; Mare Longue , December 1967, T. Cadet 1198 ( P01330236 ), September 1968, T. Cadet 1633 ( P01330235 ) .

Note—This robust species is readily distinguished from the other hairy species in the region by its overall shape (mostly deltoid to widely lanceolate vs. oblong to linear for H. capillare ), and frond size, type of trichomes, and stipe wings (large fronds, not pedunculated trichomes, and wingless stipes vs. small fronds, pedunculated trichomes and winged stipes for H. hirsutum ).

The type is cited from Madagascar, according to a little note on the original sheet. But except for this type specimen, the species has actually never been observed in the wild in Madagascar and is absent in Malagasy collections, as far as we are aware. We thus consider that the type locality is erroneous and according to the current distribution, that the type specimen would likely have been collected in the Mascarenes. Specimens ressembling H. hygrometricum have been observed and collected in the Seychelles (B. Senterre, pers. comm.), but they could also belong to the Malagasy species H. ivohibense Tardieu ( Tardieu-Blot 1941: 90, 91) that shows the same gross habit, but differs in having stipes winged at their upper part and pedunculated laminar trichomes. Additional investigations are thus needed to confirm the presence of H. hygrometricum outside of the Mascarenes.

Subgenus Mecodium

Figures

FIGURE 16.A. Hymenophyllum hirsutum (L.) Sw., as epiphyte (La Réunion, ‘Grand Etang’). B. H. hirsutum, detail of a frond showing the hairy winged stipe. C. H. hirsutum, detail of bilabiate hairy sori. D. H. hygrometricum (Poir.) Desv., as epiphyte (La Réunion, ‘Bébour’). E. H. hygrometricum, wet fronds become greener as shown here (photographs. A: J.-Y. Dubuisson; B–C: L. Bauret; D–E: C. Chaussidon).