Hymenophyllum sibthorpioides (Bory ex Willd.) Mett. ex Kuhn

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 : 29-30

17. Hymenophyllum sibthorpioides (Bory ex Willd.) Mett. ex Kuhn ( Kuhn 1868: 41), Fig. 14E, F

Trichomanes sibthorpioides Bory ex Willd. (Willdenow 1810: 498). Type:—‘Les grands bois de Bourbon’, without date, J.B.G.M. Bory de St. -Vincent s.n. (lectotype B, BW 20 204010!, here designated; isolectotype P, P00612300 !). Note: the P sheet actually indicates ‘ Ile de France’ as the locality collect, which is the former name for Mauritius, and not La Réunion (formerly named Bourbon).

= Trichomanes adianthinum Bory (Bory 1833: 78). Type :—LA RÉUNION or MAURITIUS. Without locality, without date, C. Bélanger s.n. (lectotype P, P00477836 !, here designated; isolectotype P, P00630420 !)

= Trichomanes thouarsianum C.Presl ( Presl 1843: 40). Type:—‘Habitat in insula Borbonia’, without date, L.-M.A. du Petit-Thouars s.n. (not located). Note: this name is tentatively placed here in synonymy, as the sorus margin is not described as toothed but entire.

= Hymenophyllum palmatum Bosch (van den Bosch 1859: 385), based on Trichomanes flabellatum Bory (Bory 1833: 77), non Bory ex Desv. ( Desvaux 1827: 325). Type:—‘Ile de Mascareigne’, without date, J.B.G.M. Bory de St.-Vincent s.n. (lectotype P, P00065012!, here designated; isolectotype K, K000435612!, here designated according to note of M. Tindale on the sheet). Note: The P00065012 specimen collected by Bory in ‘Ile de Mascareigne’ (former name for La Réunion) named on the sheet T. flabellatum as a new species, and secondarily identified on the sheet as H. palmatum by van den Bosch, is very likely to be part of the original material (we designated it here as lectotype). The K specimen, annoted as “part of the type collection” by M. Tindale would thus become an isolectotype.

Note: Trichomanes flabellatum Bory ex Desv. ( Desvaux 1827: 325), nom. nud., non Bosch (van den Bosch 1859: 353) is often cited as synonym. Desvaux cites as type T. flabellula d’Urv. (Dumont d’Urville 1826: 597). But Trichomanes flabellula d’Urv. is a species described by Dumont d’Urville for ‘les îles Malouines’ (Falklands). Hymenophyllum sibthorpioides is not present in the southern Atlantic region, hence explaining that we excluded this taxon for this treatment.

Trichomanes parvulum Poir. ( Poiret 1808: 64), non Copel. ( Copeland 1933: 145) is also often listed as synonym of H. sibthorpioides , but this synonymy is questionable. The original description actually does not allow clearly supporting the synonymy either to H. sibthorpioides or to the distinct Crepidomanes minutum , and the not-well preserved P type specimens (L.-M.A. du Petit-Thouars s.n.; holotype P, P00065014!; isotype P, P00065015!) could also belong to the latter species. As such this taxon could be treated as a nomem dubium, and pending additional investigations on such specimens, we propose thus to exclude it from the list.

Short description—Epiphytic; long-creeping filiform rhizomes, bearing sparsely distributed roots and long reddish-brown trichomes, and widely separated fronds; fronds glabrous, with wingless terete stipes, up to 4 cm long, slightly curled in the wild, flabellate to reniform, palmatisect with dichotomous venation; few sori, paratactic, bilabiate with a small base and with toothed margins; receptacle slightly exerted at maturity ( Fig. 14 ).

Global distribution—Western Indian Ocean, East and South Africa.

Current distribution in Mascarenes— La Réunion, Mauritius (see below)

Ecology—Epiphytic on tree-trunks in lowland to montane rainforests (100–1,500 m), and also one population in a wet ravine of the western side of La Réunion in remaining semi-dry forest.

Specimens examined— MAURITIUS. Tamatave, October 1978, D. Lorence 2006 (MAU).

— LA RÉUNION. Without locality, without date, M. Lepervanche 6 (P00065013); without locality, without date, J.B.G.M. Bory de St.Vincent s.n. (P00065012); Mare à Poule d’eau, 1835, Bernier s.n. (P00612301).

Note—This species is distinguishable by the combination of flabellate to reniform fronds and bilabiate sori with toothed margins. However, sterile specimens can be confused with sterile specimens of flabellate forms of Crepidomanes minutum , suggesting potential problems with the type specimens of supposed synonyms (see above). The species appears currently absent from Mauritius. Apart from the type of the species apparently collected in ‘Ile de France’ (an old name of Mauritius) and the specimen D. Lorence 2006 collected in 1978, the other MAU herbarium specimens are actually C. minutum var. mascarenense or C. trinerve (see Dubuisson et al. 2013). Thus, the species appears not have been observed since 1978 on Mauritius and its current presence on the island awaits confirmation.

Subgenus Sphaerocionium

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).