Abrodictyum inexpectatum Dubuisson & Rouhan, 2022

Dubuisson, Jean-Yves, Bauret, Lucie, Boucheron-Dubuisson, Elodie & Rouhan, Germinal, 2022, Abrodictyum inexpectatum, an unexpected new fern species (Hymenophyllaceae, Polypodiidae) for Madagascar, as revealed by an integrative approach, Phytotaxa 568 (1), pp. 83-91 : 88-90

Abrodictyum inexpectatum Dubuisson & Rouhan , sp. nov., Fig. 3 .

Plants similar to Abrodictyum franceae Bauret & Dubuisson , but smaller on average and with fronds plane in the wild (vs. usually crispate or curled for A. franceae ) and genetically different; also first supposedly close to A. angustimarginatum (Bonap.) J.P. Roux , but genetically different and displaying ultimate segments with more than three rows of cells on both sides of the terminal veins (vs. not more than three rows of cells for A. angustimarginatum ). It also differs from A. dregei (Bosch) Dubuisson & Rouhan in mature fronds smaller in average, usually not exceeding 13.5 cm long (reaching 37 cm for A. dregei ), lamina light green and translucent (vs. dark green and opaque), and sori obconic or cup-shaped (vs. cylindrical to slightly campanulate).

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, 25 September 2015, G. Rouhan, L. Bauret, & D. Ravelonarivo s.n. (holotype: P [ P02434058 ]!)

Epiphytic at the base of trunks or saxicolous ferns. Rhizomes short, erect, 0.5–1.0 cm in diameter, bearing long tufted, erect, red-brown and more or less catenate pluricellular hairs, densely covering apex, and numerous robust roots. Fronds clustered, semi-erect; stipes 1–3 cm long, wingless and slightly canaliculate on the adaxial surface bearing numerous scattered hairs identical to those of rhizomes; rachises, with wings on their upper part only, and main costae with hairs similar to those on the stipes and rhizomes. Laminae 5.5–10.5 × 1.5–3.5 cm, narrowly lanceolate with truncate base and acute apex, bipinnate-pinnatifid, light green and translucent, plane in the wild; pinnae 0.5–2.5 × 0.2–1.8 cm, lanceolate or ovate to narrowly oblong, sub-horizontal to oblique, basally sub-opposite then alternate; pinnules pinnatifid, lanceolate or ovate to linear, with lamina slightly decurrent along the second order costules; ultimate or terminal segments 0.2–0.4 mm wide (> 3 cells on both sides of the veins), linear and uni-veined with mostly acute (less often rounded) ends, sometimes fused by pair, the veins not reaching the margin; venation pinnate and anadromous; laminar cells thick-walled with walls up to 10 µm thick and more or less wavy, very variable in shape, mostly longitudinally oriented and sometimes oblique, tetragonal to pentagonal, less often hexagonal, isodiametric or longer than wide, especially in fused segments parts. Sori paratactic, mostly on acroscopic basal-most segments of proximal pinnules, 1.0–1.4 × 0.5–0.9 mm, usually 1 per pinnule, up to 6 per pinna, free with usually a thin full longitudinal wing on both margins or less often at the base, obconic (cup-shaped), truncate or with a slightly dilated mouth; receptacle short to long-exerted.

Distribution and habitat: —Endemic to Madagascar, in the understory of rainforests, at middle to high elevations (550–1,600 m), according to the examined specimens. The species seems to be restricted to the north-east of the island in the province of Antsiranana, but the low number of specimens attributed to this new taxon does not allow a precise definition of its distribution and abundance. Indeed, the species is either rare or has been under-collected because it has been confused with more abundant species, such as A. franceae or A. dregei . New surveys in the province and elsewhere on the island in the lowland and montane humid forests are therefore necessary.

Etymology: —The specific epithet is related to the unexpected nature of the discovery of this new species, only revealed by the molecularly sequenced specimen collected and first incorrectly identified as A. angustimarginatum .

Specimens examined (paratypes): — MADAGASCAR. Antsiranana: Partie occidentale du Massif de Marojejy de la vallée de l’Ambatoharanana au bassin supérieur de l’Antsahaberoka, 15-25 November 1959, H. Humbert 31865 ( P [ P01526301 ]!); River Ansaharatsy , 13°48’43”S, 48°47’59”E, 15 April 2000, C. Birkinshaw et al. 681 ( P [ P01627579 ]!) .

Figures

FIGURE 3. Abrodictyum inexpectatum Dubuisson & Rouhan sp. nov. A. Habitus (holotype: G. Rouhan s.n., P02434058). B. detail of fertile lamina with sori (S), scale = 5 mm. C. Detail of cup-shaped sorus (S), scale = 1 mm.