Angiopteris chongsengiana Senterre & I.Fabre, 2014

Senterre, Bruno, Rouhan, Germinal, Fabre, Isabelle, Morel, Charles & Christenhusz, Maarten J. M., 2014, Revision of the fern family Marattiaceae in the Seychelles with two new species and a discussion of the African Ptisana fraxinea complex., Phytotaxa 158 (1), pp. 57-75 : 62-64

Angiopteris chongsengiana Senterre & I.Fabre , sp.nov. Fig. 2 , Fig. 3

TYPE: — SEYCHELLES. Mahé: Mont Cotton, vallée à l'Est du Mont Cotton, au pied de Pérard, dans les hauts de la rivière Grand St. Louis , 700 m, 17 September 2011, B. Senterre & I. Fabre 6151 (holotype P!, 2-sheets P-02432630 , P-02432631 , isotype SEY! ).

Diagnosis:— This species differs from other Angiopteris with verrucose petioles by its lateral pinnae with elongate terminal pinnules and reduced distal pinnule pairs. Its venuloids are submarginal. Petioles show pinkish flesh when cut and secondary rachises are broadly winged distally.

Perennial ferns, 2–3 m tall. Rhizomes 30–65 cm tall, 30–45 cm in diameter, starchy, upright, globular to trunk-like, covered with remaining bases of old leaves, unbranched. Roots branched, stout, 7–8 mm in diameter (2 mm for secondary roots). Stipules 8–10 cm (5 cm when dry) × 7–9 cm (4 cm when dry), fleshy, apparently not proliferous, black, covered with brown scales, the scales smaller than those of the petioles, aerating areas 3–4 × 1 mm, mostly towards base of stipules, slightly immersed, elliptic, whitish, stipule margins irregularly laciniate, with narrow 1.0– 1.5 cm long lobes, radiate (not falcate), very thin, breaking off easily so that margin appears subentire. Fronds 350– 400 cm, spirally arranged, densely set, 15 cm apart, 8–12 functional fronds per plant, arching. Petioles 160–180 cm long, 5 cm in diameter, terete, rounded adaxially, with a basal pulvinus (ca. 10–15 cm long, 8 cm in diameter at base), not winged, green (when fresh), flesh pinkish inside, densely scaly especially towards base of young leaves, scales 6–9 × 0.5–0.8 mm, mixed with much smaller scales, golden brown, presence of conspicuous wart-like bases of old scales, aerating areas (15–)25–30 × 1 mm, abundant throughout up to rachis. Laminae 200–220 × 180 cm, bipinnate with undivided pinnules (basal pinnae never more than once pinnate), elliptic, longer than petiole, longer than broad. Rachises terete, rounded adaxially, not winged, green (when fresh) or yellow (when dried), sparsely pubescent or glabrescent. Pinnae petiolulate; petiolules 60 mm (up to 140 mm for basal pinnae, 10–35 mm in distal pinnae), inarticulate, rounded adaxially or with two small crests, pulvini up to 35 mm long (10–20 mm when dry), 15–18 mm in diameter at base (4–6 when dry). Pinnae alternate or rarely subopposite, 6–10 on each side of the frond, 16–24 cm apart (closer towards apex), not overlapping. Basal pinnae 85–100 × 30–38 cm, progressively and slightly reduced, perpendicular to rachis or ascendant towards apex (acrotropic), oblong or deltoid. Middle pinnae 90–94 × 35 cm, ascendant towards apex, oblong. Distal pinnae 50–54 × 24 cm, progressively and slightly reduced, ascendant towards apex, oblong or elliptic. Terminal pinnae absent, the rachis ending in a mucron. Secondary rachises terete, rounded adaxially, broadly winged distally, wings to 0.5–1.0 mm broad on either side, yellow (when dry), sparsely pubescent or glabrescent. Pinnules (observed on a middle pinna) sessile or shortly petiolulate. Secondary petiolule 0–1 mm, not articulate. Pinnules alternate to opposite, (15–)25–30 on either side, (1.6–)2.0– 2.5 cm apart, not overlapping. Basal pinnules (6–)13–18 × (1.6–) 2.2–2.5 cm, similar to other pinnules, perpendicular to rachis, elongate-lanceolate. Middle pinnules (10–)17–19 × (1.7–) 2.3–2.5 cm, perpendicular to rachis, lanceolate. Distal pinnules (6–)8–10 × 1.3–1.8 cm, typically progressively reduced, slightly ascendant towards apex (acrotropic), lanceolate. Terminal pinnules 14–25 × 2.5–3.5 cm, more developed than other pinnules, much longer and often much broader, lanceolate. Pinnule blades entire, bases slightly attenuate, symmetrical or slightly asymmetrical, margins slightly serrate with 8 teeth per cm, glabrous, slightly revolute, apices progressively acuminate (with teeth more distantly spaced, 2–3 per cm), acumen 2–3 cm long, dark green above and light green below (when fresh), membranaceous or somewhat coriaceous. Venation pinnate, midvein reaching the apex, glabrescent below, secondary veins distinct, undivided or furcate (more or less close to the midvein), 1.0– 1.5 mm apart, straight, oblique, terminating in teeth, venuloids 3–4 mm, intramarginal, ending after the line of sori, evanescent, nearly up to mid-way between the margin and the costa if observed in transparency, straight, occasionally fragmented. Sori widely set, 120–130 per pinnule, 1 row on each side of the midvein, intramarginal, 1.0– 1.5 mm from the margins, not immersed or weakly immersed, oblong, 0.6–1.2(–2.0) × 0.4 mm, not indusiate. Sporangia (8–)10–30(–40) per sorus, basally fused, mostly free above.

Representative specimens examined: — SEYCHELLES. Mahé: Congo Rouge , 540 m, 14 August 2011, B. Senterre & I. Fabre 6172 ( SEY) ; Mare aux Cochons (Mare d'Antin) , 615 m, 12 April 2012, B. Senterre & N. Labiche-Barreau 6259 ( SEY); Mont Cotton , 580 m, 17 July 2011, B. Senterre & I. Fabre 6152 ( P-02432634 , P-02432633 , SEY) ; Montagne Planneau (Mont Harrison) , 641 m, 27 July 2011, B. Senterre & I. Fabre 6158 ( SEY) , 624 m, 27 July 2011, 6160 ( SEY) , 628 m, 27 July 2011, 6162 ( SEY) ; Varigault , 585 m, 10 August 2011, B. Senterre & I. Fabre 6171 ( SEY) .

Distribution: —Only known from the granitic Seychelles; possibly endemic on the island of Mahé, where it is found in the ravines between Morne Seychellois, Pérard, Congo Rouge and Mont Cotton in the North of the island, as well as in the massif of Montagne Planneau to Varigault in the center. It has been searched for on neighbouring Silhouette Island, but was not found there, although it could be expected.

Ecology: — Angiopteris chongsengiana occurs typically in ravines of the lower montane evergreen rain forest belt, i.e. mostly at an elevation between 500 and 750–780 m above sea level. That belt, due to telescoping effect ( Senterre et al. 2009), corresponds to ca. 1500–1800(–2000) m above sea level in continental areas or larger islands at similar latitudes and is characterized by the dominance of tropical montane forest species.

Conservation: —This species is rare as it is known from only a few small populations, isolated in ca. 12 ravines of two separate mountain massifs. We estimate the number of mature individuals per ravine to ca. 10–20. The total number of mature individuals is estimated to ca. 120–250. The area of occupancy (AOO) and extent of occupancy (EOO) are respectively ca. 0.1 km ² and 17 km ². Considering IUCN criterion D (very small population, IUCN 2011: 14, 58), this species can be classified as endangered (EN). Half of the population is in the Morne Seychellois National Park and the other half is in poorly accessible areas, recently proposed to be classified as a new National Park ( Senterre et al. 2013). All populations seem healthy but with relatively limited regeneration. Invasive species are present but not abundant and we do not think that they are currently threatening these populations, although this should be assessed more carefully. If the reduced regeneration is confirmed and if it appears to be due to invasive species, then the IUCN threat category could be changed for critically endangered (CR).

Etymology: —The specific epithet honours Seychellois botanist Mr. Lindsay Chong-Seng who contributed significantly to the botany, natural history and nature conservation of the Seychelles. For visiting and local naturalists, Lindsay has since long been one of the main sources for knowledge on the Seychelles flora, practical information and guidance.

Vernacular name:— This species is relatively rare and difficult to find, and is also easily confused with the more common Angiopteris madagascariensis . Because it has only recently been recognised, it has no Creole name yet. We name it ‘Baton monsenyer-d-gran bwa’ as this species is found in more pristine forests and at higher elevations in the mountains.

Morphological affinities: —This species is distinguished by its much longer terminal pinnules of lateral pinnae compared to the distal pinnules pair of the same pinna. This character is usually well-preserved in herbarium specimens, facilitating comparisons of material. The secondary rachises are distinctly winged, which makes it easily distinguishable from the more common Angiopteris madagascariensis .

Figures

FIGURE 2. Angiopteris chongsengiana: A. Aerating areas of the petiole, B. Details of the venation and shape of pinnules, C. Distal part of a pinna showing the elongated terminal pinnule and winged rachis, D. Petiole base and ‘stipules’, E. Pinnule apex, F. Base of a middle pinna, G. Ripe sporangia. (illustrated by Katy Beaver from living and dried specimens, B. Senterre & I. Fabre 6172)

FIGURE 3. A–E: Angiopteris chongsengiana. A. View of the ‘stipules’ and rhizome (photograph by B. Senterre), B. Winged secondary rachis, with sessile pinnules (photograph by I. Fabre), C. Mature sporangia and venuloids (photograph by B. Senterre), D. Wart-like bases of old scales on petiole (photograph by B. Senterre), E. Typical apex of a pinna (photograph by I. Fabre); F–J: Angiopteris madagascariensis. F. Massive rhizome ca. 60–70 cm high (photograph by B. Senterre), G. secondary rachis not winged (photograph by I. Fabre), H. Old sporangia and venuloids (photograph by B. Senterre), I. ‘Stipule’ (photograph by I. Fabre), J. Typical aspect of the basal pinna, bipinnate on mature individuals (photograph by I. Fabre).