Hymenophyllum balfourii Baker

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 : 35-36

23. Hymenophyllum balfourii Baker ( Baker 1891: 192), Fig. 17A

Type:— LA RÉUNION. Without locality, before 1875, I. B. Balfour s.n. (holotype K, K 000435603!).

Short description—Lithophytic or epiphytic; long-creeping filiform rhizomes, bearing sparsely distributed roots and reddish-brown trichomes, and widely separated pending fronds; fronds glabrous, subsessile or with very short filiform stipes, up to 4 cm long, often less than 3 cm long, deltoid to ovate, digitate to pinnatifid, sometimes pinnate-pinnatifid with dichotomously dissected pinnae; sori few, on apical-most segments, bilabiate without a developed base but two lateral veinlets; receptacle filiform and included.

Global distribution— Madagascar and potentially in Mascarenes.

Current distribution in Mascarenes—The species awaits rediscovery on both La Réunion and Mauritius.

Ecology—Epiphytic on tree-trunks or lithophytic on wet rocks in montane rainforest usually at high elevations in Madagascar. Because of the lack of recent records in Mascarenes, we cannot define elevational range for the archipelago.

Specimens examined— MAURITIUS. Without locality, 1864, P. B. Ayres s.n. ( K000435602 ) ; Deux Mamelles , December 1972, D. Lorence s.n. ( MAU 15023 ) ; Mount Lagrave , April 1974, D. Lorence 780 ( MAU 16362 ) .

Note—According to unpublished molecular data from a Mauritian Lorence’s specimen, H. balfourii could be a dwarf form of H. inaequale (Poir.) Desv. ( Desvaux 1827: 335). The species was discovered and described on La Réunion at the end of the 19th century, and collected three times on Mauritius: the first time in 1864 with a specimen ( P. B. Ayres s.n., K 000435602) present on the same sheet as the La Réunion type by Baker, the second time on ‘Deux Mamelles’ mountain in 1972 (D. Lorence s.n., MAU 15023), and the third time on the Mount Lagrave in 1974 (D. Lorence 780, MAU 16362). The species has never been observed again on La Réunion since the original description, and its current presence on Mauritius awaits confirmation. The species could be thus considered as currently extinct on La Réunion or may be present but only at inaccessible sites at high elevations. On Mauritius, the species was observed in 1972 and 1974 as an epiphyte on respectively a tree and an Alsophila trunk in a degraded forest invaded by exotic species, as noted on the sheets. In the absence of precise location data, we have no guaranty that both populations still exist; in addition, the species has not been observed elsewhere since these last observations more than 40 years ago. Finally, in the P collections the species is only known by recent Malagasy specimens, but more investigations are required to confirm the affinity between these Malagasy specimens and the Mascarene ones. The potential rediscovery of the species can therefore be expected on both Mascarene islands.

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).