Hymenophyllum digitatum (Sw.) Fosberg

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 : 32-33

20. Hymenophyllum digitatum (Sw.) Fosberg ( Fosberg & Sachet 1980: 1), Fig. 15E–G

Trichomanes digitatum Sw. ( Swartz 1806: 370). ≡ Gonocormus digitatus (Sw.) Prantl ( Prantl 1875: 51). ≡ Microtrichomanes digitatum (Sw.) Copel. ( Copeland 1938: 36). ≡ Crepidomanes digitatum (Sw.) K.Iwats. ( Iwatsuki 1984: 175). Type:—‘Habitat in Ins. Franciae et Borboniae’, without date, without collector s.n. (holotype S?, not located). Note: a potential type is kept at P, L.-M.A. du Petit-Thouars s.n. (P00064999!).

= Trichomames digitatum Poir. ( Poiret 1808: 70), nom. illeg. Type:— MADAGASCAR. ‘Ile de Madagascar’, without date, L.-M.A. du Petit-Thouars s.n. (lectotype P, P00612304!, here designated)

= Trichomanes lanceum Willd. (Willdenow 1810: 500). ≡ Trichomanes loreum Bory (Bory 1833: 79), nom. illeg. Type:— LA REUNION. ‘Ile de Bourbon’, without date, J.B.G.M. Bory de St.-Vincent s.n. (lectotype B, BW 20 208010!, here designated; isolectotype P, P 04022563!). Note: Bory (1833: 78) proposed to rename T. lanceum as T. loreum because he considered that the concerned species does not exhibit significant lanceolate fronds and that his name was the first he has chosen before the Willdenow’s publication. However such proposition is not valid, and the Willdenow’s name, based on the same type specimen, keeps the priority and validity.

= Trichomanes piliferum Alderw. (van Alderwerelt van Rosenburgh 1922: 225). Type:—JAVA. Buitenzorg, Mt. Salak, November 1920, van den Brink 4116 (not located).

= Trichomanes taeniatum Copel. ( Copeland 1932: 6, pl. 2). ≡ Microtrichomanes taeniatum (Copel.) Copel. ( Copeland 1938: 37). Type:— TAHITI. Pare, Fautaua, 13 May 1930, M.L. Grant 3561 (holotype US, US 00134628!).

= Trichomanes digitatum Sw. var. uluguruense Reimers ( Reimers 1933: 912). Type :— TANZANIA. ‘ Uluguru-Gebirge : NW., Bondua’, 25 November 1932, H.J. Schlieben 3028 (holotype B, BW 20 0104376!; isotype B, BW 20 0104375!, BR, BR0000013204945 !, BR0000013204952 !).

= Hymenophyllum alternatum Fosberg ( Fosberg 1950: 135), based on Trichomanes dichotomum Kunze ( Kunze 1847: 302, nom. nud.; 1848: 285), nom. illeg. ≡ Gonocormus dichotomus (Kunze) Prantl ( Prantl 1875: 51). ≡ Microtrichomanes dichotomum (Kunze) Copel. ( Copeland 1938: 36). Type:—JAVA. Salak, November 1843, H. Zöllinger 1707 (type P, P00624455!).

Note: Tardieu-Blot (1951) also cites Trichomanes blumei Hassk. as a synonym, but despite information provided by Tropicos and IPNI, we did not succeed in finding any publication from Hasskarl including the description of the species. The only study we found on ferns by Hasskarl (published in 1856-1857) concerns Gleicheniaceae and tree-ferns from Java ( Hasskarl 1856).

Short description—Epiphytic; long-creeping filiform rhizomes, bearing sparsely distributed roots and long reddish-brown trichomes, and widely separated pending fronds; fronds with filiform wingless stipes, up to 5 cm long, palmate to mostly digitate, bearing marginal isolated minute black hairs ( Fig. 15F ), quite rare to absent on old leaves / specimens; sori few, terminal on most-apical segments, with a well-developed campanulate part, two lateral veinlets and a dilated bilabiate mouth; receptacle included to exerted at full maturity ( Fig. 15G ).

Global distribution—East tropical Africa to Pacific Islands.

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

Ecology—Usually epiphytic on the Mascarenes (reported as mostly lithophytic in Asia) on tree-trunks in lowland to montane rainforests (400–1,700 m).

Representative specimens examined— MAURITIUS. Without locality, without date, F. W. Sieber s.n. ( P04022565 ) ; Brise Fer, December 2012, K. Pynee et al. s.n. ( MAU 0009345 ) ; Rivière du Poste, March 2012, K. Pynee et al. s.n. ( MAU 0011494 ) ; Mt Cocotte , October 2012, K. Pynee et al. s.n. ( MAU 0011914 ) ; Plaine Paul, January 2013, K. Pynee et al. s.n. ( MAU 0012600 ) ; Pétrin, February 2016, K. Pynee et al. s.n. ( MAU 0017695 ) .

— LA RÉUNION. Without locality, 1831, C. Bélanger s.n. ( P0422564 ) ; Plaine des Palmistes , July 1875, M. G. de L’Isle 354 ( P00065000 ) ; Roche écrite, April 2005, T. Janssen et al. 2750 ( P00590831 ) .

Note— Hymenophyllum digitatum is the only Hymenophyllum species on the Mascarenes and in the western Indian Ocean that has sori with a developed campanulate part ( Fig. 15G ), a feature that usually characterizes trichomanoids. This explains that most of the described related species were first placed in Trichomanes and that the Mascarenan species is named T. digitatum in Tardieu-Blot (1951, 2008). The taxonomic position of this species and relatives has actually been questionable and discussed for a long time. Copeland (1938) included these species in his genus Microtrichomanes (Mett.) Copel. , based on Microtrichomanes Mett. ( Mettenius 1864: 413, 414), considering such a genus as intermediate between Hymenophyllum and traditional Trichomanes (currently trichomanoids). The species actually combines Trichomanes -like sori and Hymenophyllum -like gross habit. Ebihara et al. (2004) nevertheless clearly demonstrated that most Microtrichomanes species, including traditional T. digitatum , belong to Hymenophyllum and more specifically to subgenus Sphaerocionium . Except for the sorus shape, Microtrichomanes taxa share with the other species of Sphaerocionium a laminar marginal indumentum, even if reduced.

Figures

FIGURE 15. A. Hymenophyllum capillare Desv., typical form, as epiphyte (La Réunion, ‘Forêt de Bon Accueil, Les Makes’). B. H. capillare, typical form, detail of fronds. C. H. capillare f. nanum Hennequin & Dubuisson, f. nov., as epiphyte (La Réunion, ‘Pitons Mare à Boue’). D. H. capillare f. nanum, habit, type individual, scale = 0.5 cm (La Réunion, ‘Forêt de Bon Accueil, Les Makes’, J.-Y. Dubuisson & L. Bauret HR 2016-10, P). E. H. digitatum (Sw.) Forsberg, as epiphyte (La Réunion, ‘Forêt de Bon Accueil, Les Makes’). F. H. digitatum, detail of laminar margin showing minute dark trichomes. G. H. digitatum, detail of fronds and sori with tubular bases (s) (photographs.A–B: L. Bauret; C–G: J.-Y. Dubuisson).