Abrodictyum cylindratum Dubuisson, 2017

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 : 209

Abrodictyum cylindratum Dubuisson , sp. nov., Fig. 1A, B

Resembles A. parviflorum (Poir.) Bauret & Dubuisson but has sub-sessile fronds or with short stipes and a typical narrowly oblong to linear cylindrical brush-like shape, while brush-like A. parviflorum forms display distinct larger stipes and elliptic to lanceolate fronds.

Type:— MADAGASCAR. Antsiranana, Andapa. Parc National de Marojejy, Abords du camp 4 et le long de la rivière, 14°26’43’’S, 49°44’31’’E, 1575 m, 25 September 2015, G. Rouhan et al. 1595 (holotype P, P02434066).

Terrestrial ferns, sometimes epiphytic on the base of trunks. Rhizomes erect to short-creeping, 0.7–1.6 cm in diameter, bearing long tufted erect red-brown trichomes, especially densely covering apex, and numerous robust roots. Fronds clustered, erect; stipes quite short (the fronds appearing sometimes sub-sessile) 0.4–4 cm long, mostly canaliculate, wingless, bearing numerous scattered trichomes identical to those present on rhizomes; rachis with trichomes similar to those on the stipes and rhizomes. Laminae (10–)12–35(–40) × 2–4 cm, narrowly oblong to linear, with obtuse apex and obtuse to decurrent base, pinnate to bi-pinnate with deeply dichotomously dissected pinnules, translucent, with pinnae and pinnules oriented in three dimensions, the fronds having thus a narrowly cylindrical brush-like shape; pinnae 0.5–2.5 × 0.4–1.5 cm, sub-horizontal to oblique, the basal-most usually quite reduced to one or few segments, usually lanceolate to ovate or linear; ultimate segments 0.10–0.15 mm wide and usually long (up to 0.8 cm), capillary with a thin lamina rarely exceeding 1 row of cells on both sides of the veins (max. 3), linear and single-veined with acute to rounded ends; main venation pinnate and anadromous. Sori paratactic, located mostly on acroscopic basal-most segments of proximal pinnules, 0.80–1.25 × 0.5–0.8 mm, usually numerous, up to 12 per pinna, free, obconic, truncated; receptacle short to long-exerted.

Etymology: —The specific Latin epithet cylindratum refers to the cylindrical brush-like shape of the fronds.

Distribution and habitat: —Endemic to Madagascar, usually terrestrial in the understory of rainforests, more rarely epiphytic on the base of trunks, from low to middle elevations (400–1,700 m). According to specimens in collections, this species seems restricted to the Andapa district (Anajanaharibe and Marojejy). But because of potential confusion with A. parviflorum (Poir.) Bauret & Dubuisson , its real distribution needs further investigation ( Table 1).

Specimens examined: — MADAGASCAR. Antsiranana: Andapa, Anjanaharibe, December 1950, G. Cours 3762 (P01526566); Andapa, Marojejy, December 1945, H. Humbert 22457 (P01526552);Andapa, Marojejy, December 1959, H. Humbert 31748 (P01526551, P0152549); Andapa, Marojejy, environs du Camp 2, October 1956, H. des Abbayes 3072 (P01526559); Andapa, Marojejy, October 1988, J.S. Miller 3548 (MO, P01526547); Andapa, RNI 12 du Marojejy, October 1996, F. Rakotondrainibe 3476 (P00084974); Andapa, Anjanaharibe-Sud, September 1997, Birkinshaw et al. 482 (MO, P01526564); Andapa, Parc National de Marojejy, Petit vallon à proximité du Camp 3, bas-fond, October 2011, G. Rouhan et al. 1219 (P02432757); Andapa, Parc national de Marojejy, Abords de la piste entre camp 2 et camp 3, September 2015, G. Rouhan et al. 1571 (P02434062); G. Rouhan et al. 1583 (P02434065). Province unknown: January 1949, G. Cours 3273 (P01526568).

Note: —The present phylogeny ( Fig. 3 ) shows that the Malagasy atypical, cylindrical, A. meifolium specimen used for the molecular investigation is not included into the robust meifolium clade and could thus be a distinct taxon. After having studied carefully the Malagasy specimens stored at P, we could identify many specimens resembling the latter (see here-above). Those specimens ( Fig. 1A, B ) have fronds which are often sub-sessile or with rather short stipes that usually do not exceed 4–5 cm long, whereas typical A. meifolium have clearly stipitate fronds with stipes that usually exceed 4–5 cm ( Fig. 1C, D ). In addition, the “atypical” specimens display quite narrowly oblong to linear brush-like laminae giving them a distinctive narrowly cylindrical shape. By contrast, typical A. meifolium has its lamina varying from narrowly elliptic to lanceolate but never narrowly cylindrical ( Fig. 1C–E ). The morphological differences and the phylogeny results allow us to describe here a new Malagasy species for the narrowly cylindrical specimens with quite short to reduced stipes. This narrow cylindrical species, named here Abrodictyum cylindratum Dubuisson , is restricted to Madagascar, and according to P specimens would have been observed only in the Andapa district, whereas the other A. meifolium variants now referred to as A. parviflorum comb. nov. (see here-after) are found in La Réunion, Seychelles in addition to Madagascar. It seems thus that A. cylindratum has not colonized the other western Indian Ocean islands contrary to A. parviflorum .

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 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.