Abrodictyum pseudorigidum Bauret & Dubuisson, 2016

Dubuisson, Jean-Yves, Bauret, Lucie, Grall, Aurelie, Li, Tian, Ebihara, Atsushi & Hennequin, Sabine, 2016, Discussion on the taxonomy of African fern Abrodictyum rigidum (Sw.) Ebihara & Dubuisson and description of two new Abrodictyum C. Presl species (Hymenophyllaceae, Polypodiidae) for the Afro-Malagasy region, Phytotaxa 284 (3), pp. 151-168 : 161

Abrodictyum pseudorigidum Bauret & Dubuisson , sp. nov., Fig. 6

Plants mainly similar to Abrodictyum rigidum (Sw.) Ebihara & Dubuisson , but restricted to the Afro-Malagasy region (versus the Neotropics for A. rigidum ) and genetically distinct.

TYPE:– MADAGASCAR. Fianarantsoa, Ambatomboay, RNI d’Andringitra versant E ; 40 km au Sud d’Ambalavao, sur les berges d’un affluent de la rivière Sahavatoy, 24 May 1995, F. Rakotondrainibe 2708 (holotype P, P00059914 ) .

= “ Trichomanes dregei Bosch ” (1858: 372). Type :– SOUTH AFRICA. Natal , Transkei , Lusikisiki, J. F. Drège s.n. (holotype P?, not located; isotype? S-P-18091!). Note:— Van den Bosch did not provide any description for this species and only a reference to South-African Trichomanes rigidum sensu Kunze (1836) based on specimens collected by Drège. We cannot accept this name as valid.

= Trichomanes rigidum Sw. var. lugubre H. Christ (1901: 849) . Type:– DRC. Kisantu, J.B. Gillet s.n. (holotype BR, BR 0000013468675!).

= Trichomanes rigidum Sw. var. annobonense Brause (1915: 378) . Type:– EQUATORIAL GUINEA. Annobon Island: Gipfel der Santa Mina, Nebelwald mit Baumfarnen, 650 m ü. M., October 1911, G.W.J. Mildbraed 6700 (holotype B, B 20 0093175!).

Terrestrial ferns. Rhizomes short, erect, 0.5–2.0 cm in diameter, bearing long tufted erect red-brown more or less catenate pluricellular trichomes, especially densely covering apex, and numerous robust roots. Fronds clustered, erect; stipes (2–)11–16(–26) cm, cylindrical to mostly canaliculate, wingless or narrowly winged at their upper part only, bearing numerous scattered trichomes identical to those present on rhizomes; rachis and main pinna axes with trichomes similar to those on the stipes and rhizomes. Laminae (8.0–)10.0–26.0(–31.0) × (3.0–)7.5–16.0(–19.0) cm, mostly triangular, less often sub-lanceolate to narrowly ovate, with more or less lanceolate to attenuated apex, tripinnatepinnatifid; pinnae (2.0–)3.5–7.0(–9.0) × 0.5–2.0(–3.5) cm, horizontal to oblique, basally sub-opposite then alternate, lanceolate, or triangular to linear, coriaceous, dark green and more or less opaque; pinnules pinnatifid to bipinnatifid (up to tripinnatifid for the largest specimens), lanceolate to linear, with lamina slightly decurrent along the second order rachises; ultimate segments 0.2–0.4 mm wide, linear and uni-veined with acute to rounded ends, the veins not reaching the margin; venation pinnate and anadromous; laminar cells thick-walled with walls up to 25 μm thick and more or less wavy, tetragonal to pentagonal, nearly isodiametric to twice longer than wide. Sori paratactic, located mostly on acroscopic basal-most segments of proximal pinnules, 1.0–2.0 × 0.6–0.9 mm, 1–3(–6) per pinnule, up to 20 (sometimes more than 30) per pinna, free with a thin wing mostly at the base, cylindrical, truncated to slightly bilabiate with a slightly dilated mouth; receptacle short to long-exerted.

Distribution and habitat: —Sub-Saharan wet tropical Africa to western Indian Ocean islands, terrestrial in the understory of rainforests from low to high elevations (200–2,500 m).

Etymology: —The epithet refers to the Neotropical species Abrodictyum rigidum under which A. pseudorigidum was firstly named and with which it is often confused in the wild and in collections.

Specimens examined: see Appendix 1.

Figures

FIGURE 6. Abrodictyum pseudorigidum Bauret & Dubuisson, sp. nov. (F. Rakotondrainibe 2708, holotype P00059914). A. Habitus; B. Detail of a pinna, the arrows show some of the sori; C. Detail of a terminal pinnule with a basal sorus; D. Detail of indusium; E. Detail of laminar cells, the arrow shows the margin.