Abrodictyum tamarisciforme (Jacq.) Ebihara & Dubuisson (2006: 244)

Dubuisson, Jean-Yves, Bauret, Lucie, Grall, Aurelie, Senterre, Bruno, Said, Ahamada H., Pynee, Kersley, Ebihara, Atsushi & Hennequin, Sabine, 2017, Taxonomic study of the fern genera Abrodictyum C. Presl and Trichomanes L. (Hymenophyllaceae, Polypodiidae) in the western Indian Ocean, and description of a new Abrodictyum species for Madagascar, Phytotaxa 327 (3), pp. 201-222 : 214-215

Abrodictyum tamarisciforme (Jacq.) Ebihara & Dubuisson (2006: 244) .

Trichomanes tamarisciforme Jacq. (1791[1789]: 285). Type:— LA REUNION. ‘Sponte crescit in insula Borboniae’, without date, without collector (holotype W?).

= Trichomanes stylosum Poir. (1808: 82) , syn. nov. ≡ Selenodesmium stylosum (Poir.) Copel. (1938: 81) . ≡ Abrodictyum stylosum (Poir.) J.P. Roux (2009: 38) . Type:— MADAGASCAR. Without locality, without date, L.-M.A. du Petit-Thouars s.n. (holotype P, P00482618!; isotype P, P00482633!).

= Trichomanes achilleifolium Bory ex Willd. (1810: 512) , as ‘ achilleaefolium ’, syn. nov. Type:—“Ile de France & de Bourbon”, J.B.G.M. Bory de St.-Vincent s.n. (holotype B, BW 20 214010!).

Epiphytic, more rarely lithophytic ferns. Rhizomes short-creeping, 0.5–0.8 cm in diameter, bearing long tufted erect red-brown trichomes, especially densely covering apex, and numerous robust roots. Fronds clustered, erect or often appearing pending in epiphytic specimens in the wild; stipes 6–12(–15) cm long, canaliculate, wingless, bearing numerous scattered trichomes identical to those present on rhizomes; rachises with wing on their upper part, and rachises and main pinna axes with trichomes similar to those on the stipes and rhizomes. Laminae (20–)25–35 × 4–8(–12) cm, plane, usually lanceolate, less often oblong or ovate, with attenuated apex and rounded or obtuse to decurrent base, appearing often falciform because of a curved rachis, usually bi-pinnate-pinnatifid, less often tri-pinnate-pinnatifid, light green and translucent; pinnae 2–4(–7) × 1–3 cm, sub-horizontal to oblique, basally sub-opposite then alternate, usually lanceolate and often appearing falciform, or ovate to oblong, and pinnate; pinnules pinnatifid or less often more divided, lanceolate to oblong or ovate; ultimate segments 0.25–0.40 mm wide, with usually 4(5) rows of lamina cells on both sides of the veins including a clearly distinct margin, linear and single-veined, often dichotomously and shortly divided at the pinnule apex, with acute to rounded ends, the veins reaching or not the distinct marginal row of cells; venation pinnate and anadromous. Sori paratactic, mostly on acroscopic basal-most segments of proximal pinnules, 0.8–1.0 × 0.6–0.8 mm, 2–3(–6) per pinnule, up to 30 or more per pinna, free with a thin wing on their base, obconic, usually truncated or with a slightly dilated mouth; receptacle short to relatively long-exerted (up to 1 cm long).

Distribution and habitat: — Madagascar and Mascarenes, and awaits confirmation in Comoros where it has not been yet observed, usually epiphytic, often on tree fern trunks, less often lithophytic (especially in Mauritius), in the understory of rainforests, from low to middle elevations (250–1,700 m).

Representative specimens examined: — MADAGASCAR. Antsiranana: Andapa, montagne d’Ambatosoratra , January 1949, G. Cours 3336 (P) ; Île de Nossi-Be, April 1841, M. Pervillé?769 (P01596748) ; Sambava, Marogaona, Ambodimanga , forêt de Makirovona, December 2013, Rakotonirina et al. 351 (P) . Fianarantsoa: Cascade de Ranomena , 1834, Bernier 26 (P). Province unknown: without locality, without date, without collector (P01331303) .

— MAURITIUS. Without locality, without date, without collector (P01381686) ; without locality, without date, without collector (P01381687); without locality, without date, P. Commerson s.n. (P01485626); Pétrin, area above Black River Gorges , October 1974, Barclay 3329 (MAU) ; Bar Le Duc , inside private hunting zone, December 2012, K. Pynee et al. s.n. (MAU 0009261) ; Grand Bassin, Gouly Père Nature Reserve , October 2015, Gungadurdoss et al. s.n. (MAU 0019238) ; Pétrin, State Land Raoul, next to road to Grand Bassin , February 2016, K. Pynee et al. s.n. (MAU 0019004, MAU 0019005) ; Brise Fer, Next Conservation Management Area , February 2016, K. Pynee et al. s.n. (MAU 0011485) .

— LA REUNION. Plaine des Fougères, 1850, M. Boivin s.n. (P01430194); without locality, before 1857, P. Commerson 1480 (P00674943); without locality, without date, Richard 298 (P01430186); Cilaos, November 1973, F. Badré 907 (P01596683); Takamaka, May 1974, J. Bosser 22047 (P01596685); Takamaka, May 1976, J. Bosser 22241 (P01596679); Saint Philippe, Forêt de Mare Longue, April 1999, J.-Y. Dubuisson HR-1999-11 (P); Saint Philippe, Forêt de Mare Longue, April 2002, J.-Y. Dubuisson HR-2002-15 (P02433297).

Note: — Abrodictyum tamarisciforme is relatively abundant as large epiphytes in montane forests, especially in La Réunion, mostly on tree-fern trunks ( Alsophila spp. ) ( Grangaud et al. 2010; pers. obs.; Fig. 5 ). In the field, the species is thus well distinguishable from typical terrestrial A. rigidum -like taxa ( A. pachyphlebium , A. pseudorigidum , and A. franceae ), but some specimens can occasionally be found as terrestrial or lithophytic (especially in Mauritius), and A. tamarisciforme could be confused in collections with the species cited above, and with the plane forms of A. parviflorum comb. nov. (see Fig. 1D, E ). Nevertheless precise anatomical investigations on herbarium and wild specimens reveal that the lamina of A. tamarisciforme is bordered by a clearly observable distinct marginal row of cells ( Fig. 2G ). This feature has never been described previously and therefore appears diagnostic of the species, permitting for example the validation of the identification of ambiguous lithophytic Mauritian specimens. Abrodictyum stylosum ( Poiret 1808: 82) J.P. Roux (2009: 38) , characterized by very long sorus receptacles as indicated by the specific epithet, is considered by Roux (2009) as a distinct species, but its type specimen (L.-M.A. du Petit-Thouars s.n., P00482618) and the type of its supposed synonym T. achilleifolium Bory ex Willd. (1810: 512) (J.B.G.M. Bory de St.-Vincent s.n., BW 20 214010) share all the morphological and anatomical characters of A. tamarisciforme including the distinct marginal row of cells. Therefore we propose to consider A. stylosum (and its synonyms) as a synonym of A. tamarisciforme .

Genus Trichomanes Linné (1753: 1097)

The genus Trichomanes (sensu Ebihara et al. 2006) is represented by more than 60 species globally. Most species are neotropical and the genus is represented in the Palaeotropics by 5 species only: T. crispiforme and T. guineense in western Africa, and T. boivinii , T. cupressoides and T. madagascariense in the western Indian Ocean. Trichomanes cupressoides is endemic to the Seychelles and its description and taxonomy were discussed by Bauret et al. (2015). Trichomanes boivinii is found in Madagascar and Comoros ( Mayotte; Saïd et al. 2017), and T. madagascariense is endemic to Madagascar, and seems restricted to Masoala peninsula (pers. obs). Trichomanes boivinii and T. madagascariense are close species, sharing a short-creeping rhizome. The former is usually bi-pinnate-pinnatifid, while the latter is simply-pinnate ( Fig. 6 ). The pinnules of the former resembles the pinnae of the latter, both respective pinnules and pinnae being lobed, with lobes multi-veined and with a toothed margin ( Fig. 2H, I ). Such features easily allow their distinction from the Abrodictyum species in the region.

Figures

FIGURE 1. Polymorphism in lamina shape of some similar Abrodictyum species in the western Indian Ocean. A. Narrowly cylindrical brush-like Malagasy A. cylindratum Dubuisson sp. nov. (G. Rouhan 1219; photograph by G. Rouhan). B. Habitus of a narrowly cylindrical brush-like Malagasy A. cylindratum Dubuisson sp. nov.(G. Rouhan et al. 1595, P02434066). C. Habitus of La Réunion A. meifolium (Bory ex.Willd) Ebihara & K.Iwats. exhibiting the shape of the species type with elliptic-lanceolate brush-like fronds (J.-Y. Dubuisson HR-2003- 2, P). D. Habitus of La Réunion A. meifolium with lanceolate plane fronds, specimen with such frond shape would correspond to distinct Trichomanes parviflorum Poir. according to Tardieu-Blot (2008) (J.-Y. Dubuisson HR-2003-2, P). E. Plane form of T. parviflorum in the wild, La Réunion (photograph by L. Bauret).

FIGURE 2. Anatomical details of pinnae, pinnules and segments for Abrodictyum and Trichomanes species of the western Indian Ocean. A. Capillary segments with a thin lamina of one row of cells of brush-like A. meifolium (Bory ex Willd.) Ebihara & K.Iwats (J.-Y. Dubuisson HR-2003-2, P). B. Details of capillary segments of brush-like A. meifolium (J.-Y. Dubuisson HR-2003-21, P). C. Segments with thin lamina of A. meifolium (H. Humbert 17766, P01526554), such similar segments are also observed in plane T. parviflorum Poir. D. Details of segments with thin lamina of A. meifolium (H. Humbert 17766, P01526554), such similar segments are also observed in plane T. parviflorum. E. Segments with homogeneous thin lamina of A. angustimarginatum (Bonap.) J.P. Roux (F. Rakotondrainibe 6392, P00244962, first identified as T. aff. meifolium). F. Pinnules of A. pachyphlebium (C.Chr.) Bauret & Dubuisson (G. Rouhan et al. 331, P00749278). G. Segments of A. tamarisciforme (Jacq.) Ebihara & Dubuisson with the particular distinct marginal row of cells (as detailed in inset) (J.-Y. Dubuisson HR-2002-15, P02433297). H. Pinnules of T. boivinii Bosch (F. Rakotondrainibe 1788, P00100302). I. Pinnae of T. madagascariense (Bosch) T. Moore (G. Rouhan et al. 367, P00749322).

FIGURE 5. Abrodictyum tamarisciforme (Jacq.) Ebihara & Dubuisson A. As epiphytes on a tree fern trunk in montane forest in La Réunion (photograph by L. Bauret). B. Habitus (J.-Y. Dubuisson HR-1999-11, P).

FIGURE 6. A. Habitus of Trichomanes boivinii Bosch (F.Rakotondrainibe 1788, P00100302). B. Habitus of T.madagascariense (Bosch) T.Moore (G. Rouhan et al. 367, P00749322).