Abrodictyum cylindratum Dubuisson, 2017

Abrodictyum cylindratum Dubuisson View in CoL , sp. nov., Fig. 1A, B View FIGURE 1

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 View FIGURE 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 View FIGURE 1 ) 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 View FIGURE 1 ). 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 View FIGURE 1 ). 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 .