Abrodictyum pachyphlebium (C.Chr.) Bauret & Dubuisson (2015: 8)

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 : 210-211

Abrodictyum pachyphlebium (C.Chr.) Bauret & Dubuisson (2015: 8) .

Trichomanes pachyphlebium C.Chr. in Bonaparte (1920b: 16, 17). Type:— MADAGASCAR, L. Humblot 451 (holotype P, P00482607!; isotype K, P00482606!).

Terrestrial ferns. Rhizomes short, erect, 0.8–1.5 cm in diameter, bearing long tufted erect red-brown trichomes, especially densely covering apex, and numerous robust roots. Fronds clustered, erect; stipes 4–12 cm long, cylindrical to canaliculate, slightly winged, bearing numerous scattered trichomes identical to those present on rhizomes; rachis slightly winged and with trichomes similar to those on the stipes and rhizomes. Laminae (8–)10–20(–25) × 4–12 cm, lanceolate to triangular, with attenuated apex and truncate to obtuse base, bi-pinnate-pinnatifid, coriaceous, dark green and more or less opaque; pinnae 2.0–6.0 × 0.5–2.0 cm, horizontal to oblique, basally sub-opposite then alternate, lanceolate to oblong; pinnules lobed to pinnatifid, linear or elliptic to ovate, and often spatulate with proximal ultimate segments linear and entire and distal ultimate segments more or less fused with acute ends, pinnule apices appearing thus multi-veined and more or less serrate to serrulate; venation pinnate and anadromous. Sori paratactic, located mostly on the acroscopic basal-most segment of the basal-most pinnules, usually a single sorus per pinnule, 1.5–2.0 × 0.8–1.0 mm, free, cylindrical to narrowly campanulate, truncated or with a very slightly dilated mouth; receptacle short to long-exerted.

Distribution and habitat: —Endemic to Madagascar, restricted to north-eastern coast (incl. Masoala peninsula), terrestrial in the understory of rainforests from low to middle elevations (100–1,000 m) ( Table 1).

Specimens examined: — MADAGASCAR. Antsiranana: Antalaha, Masoala, 25 February 2001, A. Rasolohery 331 (P00338537). Fianarantsoa: Ambalavao, Limite extérieure nord de la RS d’Ivohibe, 9 September 1997, F. Rakotondrainibe et al. 4081 (P00134095). Toamasina: Maroansetra, 20 October 2004, G. Rouhan et al. 331 (P00749278, P00749279).

Note: —This species was initially thought to be close to the Neotropical Trichomanes elegans Rich. (Christensen in Bonaparte 1920b) and was still included in the genus Trichomanes in Roux’s synopsis (2009). Bauret et al. (2015) placed it under the genus Abrodictyum on the basis of molecular evidence. With its general frond shape ( Fig. 4B ), this species can be confused in the wild with the A. rigidum -like species (now referred to A. pseudorigidum and A. franceae ; Dubuisson et al. 2016) and is molecularly closely related to the Malagasy A. franceae . Nevertheless, its distinction from both other species can be made on a precise observation of the pinnules. In A. pseudorigidum and A. franceae , the pinnules are pinnate or pinnatifid with all ultimate segments clearly linear, free and single-veined. In A. pachyphlebium , pinnules are lobed to pinnatifid, linear (for the most-proximal ones) or more often elliptic to ovate and spatulate with proximal segments free and the distal ones more or less fused, often by pair ( Fig. 2F ). The apices of pinnules appear therefore mostly multi-veined and more or less serrate to serrulate. Observations on herbarium specimens must be done carefully because ultimate segments in many individuals of A. pseudorigidum can overlap or be connivent, especially if short, and could appear fused but are not.

Figures

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 4. A. Habitus of Abrodictyum angustimarginatum (Bonap.) J.P.Roux (L. Bauret et al. 144, P02434057). B. Habitus of A. pachyphlebium (C.Chr.) Bauret & Dubuisson (G. Rouhan et al. 331, P00749278).