Abrodictyum angustimarginatum (Bonap.) J.P. Roux (2009: 37)

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 : 207-208

Abrodictyum angustimarginatum (Bonap.) J.P. Roux (2009: 37) .

Trichomanes angustimarginatum Bonap. (1925: 12, 13). ≡ Macroglena angustimarginata (Bonap.) Copel. (1938: 84) . Type:— MADAGASCAR. ‘Région de l’Est. Près de Beforona. Forêt orientale. Sur les troncs pourris. Vers 700 mètres d’altitude, Novembre

1921’, H. Perrier de la Bâthie 14286 (holotype P, P00466435!; isotypes P, P00466433!, P00466434!).

Mostly epiphytic ferns, occasionally lithophytic. Rhizomes short, erect, 0.3–1.0 cm in diameter, bearing long tufted erect red-brown trichomes, especially densely covering apex, and numerous robust roots. Fronds clustered, usually pendent; stipes (2–)3–4(–6) cm long, cylindrical, wingless, bearing numerous scattered trichomes identical to those present on rhizomes; rachis slightly winged on its upper part and with trichomes similar to those on the stipes and rhizomes. Laminae (8–)10–15(–20) × (1–) 2–5 cm, plane, narrowly lanceolate to mostly narrowly oblong or linear, with attenuated apex and decurrent base, bi-pinnate to tri-pinnate, translucent and light green; pinnae 0.5–3.0 × 0.3–0.5(– 0.8) cm, with trichomes similar to those on the rachis on their base, sub-horizontal to oblique, basally sub-opposite then alternate, lanceolate to (ob)ovate, less often triangular; pinnules dichotomous; ultimate segments 0.2–0.3 mm wide with a thin homogeneous lamina not exceeding 3 rows of cells on both sides of the veins, linear and single-veined with acute to rounded ends, the veins not reaching the margin; main venation pinnate and anadromous. Sori paratactic, located mostly on acroscopic basal-most segments of pinnae or of proximal pinnules, 0.8–1.2 × 0.6–0.9 mm, often a single sorus and less often 3–6 sori per pinna, free with a thin wing mostly at the base, obconic and truncated; receptacle short to long-exerted.

Distribution and habitat: —Endemic to Madagascar, mostly epiphytic on tree-fern trunks, occasionally lithophytic or more rarely terrestrial, in the understory of rainforests from low to middle elevations (500–1,200 m) ( Table 1).

present study.

Specimens examined: — MADAGASCAR. Antsiranana: Andapa, RNI 12 du Marojejy, October 1996, F. Rakotondrainibe et al. 3438 (P00084918) ; Doany, PN de Marojejy, October 2001, F. Rakotondrainibe et al 6338 (P00244893); Doany, PN de Marojejy, October 2001, F. Rakotondrainibe et al. 6392 (P00244962); Andapa, September 2015, G. Rouhan et al. s.n. (P02434058). Toamasina: Ambatondrazaka, Parc national de Zahamena, June 2001, Rasolohery 548 (P00233475) ; Ambatondrazaka, 1 October 2015, Bauret et al. 144 (P02434057) .

Note: —This endemic Malagasy species has narrowly oblong fronds and thin segments ( Fig. 4A ) and is morphologically close to A. parviflorum (Poir.) Bauret & Dubuisson comb. nov. (formerly considered as A. meifolium ) and the distinct cylindrical forms corresponding to A. cylindratum Dubuisson sp. nov. (as presented here-after). Consequently, A. angustimarginatum can easily be confused with both species (see Fig. 1 ). However, the fronds of A. angustimarginatum are always plane whereas those of A. cylindratum sp. nov. always have a brush-like shape. Furthermore, the brush-like A. parviflorum comb. nov. and A. cylindratum sp. nov. specimens always exhibit capillary segments whereas all A. angustimarginatum specimens clearly show a more or less homogeneous thin lamina that does not exceed 3-cells along the veins (see Fig. 2E ). Finally, A. angustimarginatum is often observed as epiphytic on tree fern trunks, often with pending fronds, while A. parviflorum comb. nov. is mostly terrestrial and quite occasionally epiphytic on the base of trunks usually with clearly erect fronds (as also shown for A. cylindratum sp. nov., see Fig. 1A ). Such morphological and ecological differences in addition to phylogeny ( Fig. 3 ) allow us to maintain A. angustimarginatum as a distinct species.

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 3. Bayesian phylogeny inferred fromrbcL sequences showing relationshipswithin genus Abrodictyum (notedA) andTrichomanes (noted T). Support values on nodes are posterior probabilities. The new taxonomic treatment discussed here is indicated on the right. Taxa in coloured boxes represent Afro-western Indian Ocean clades here noted α and β as discussed in the text.

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).