Ptisana laboudalloniana Senterre & I.Fabre, 2014

Ptisana laboudalloniana Senterre & I.Fabre , sp.nov. Fig. 4 View FIGURE 4

TYPE:— SEYCHELLES. Mahé: Montagne Planneau (= Mont Harrison), crête au Sud du sommet , 628 m, 27 July 2011, B. Senterre & I. Fabre 6161 (holotype P!, 2 sheets P-02432635 , P-02432636 , isotype SEY!, 2 sheets ).

Diagnosis:—This species is characterized by its secondary rachises widely winged along most of their length, few pinnae, 2–4 pairs, petioles 1.0– 1.6 m long, erect, verrucose, brownish to purplish on fresh, laminae shorter than the petioles and shorter than broad, pinnules not thick, not fleshy, (sub)sessile, with an apex progressively narrowed, and intramarginal synangia.

Perennial ferns, 1.6–2.4 m. Rhizomes 18–20 × 15–20 cm in diameter, upright, globular, covered with remaining bases of old leaves. Roots branched, stout, 7 mm in diameter. Stipules 7.0 × 5.5 cm (when fresh), fleshy, rarely proliferous (observed once), glabrescent, with or without visible aerating areas, surface irregular, stipule margins entire, irregularly cracked. Fronds 190–260 cm, spirally arranged, densely set, 10 cm apart, ca. 4 functional fronds per plant, strongly ascending. Petioles 100–160 cm long, 3–4 cm in diameter, terete, rounded adaxially, with a basal pulvinus (ca. 5–7 cm long, 5 cm in diameter at base), not winged, yellow (when dry), purple or brown to black (when fresh), flesh pinkish inside, densely scaly (on young leaves), scales 6–7 × 1.5–2.0 mm, mixed with caducous narrower scales (1–3 cells wide), golden brown, with strong wart-like bases of old scales (almost prickly on old leaves), aerating areas abundant throughout up to rachises, 20–40 × 1–2 mm. Laminae 90–100 × 125–130 cm, bipinnate with undivided pinnules, rhomboidal, shorter than the petiole, shorter than broad. Rachises terete, rounded adaxially, not winged, yellow (when dry), green (when fresh), glabrous. Pinnae petiolulate. Petiolules (40–) 50–70 mm (up to 100 mm in basal pinnae, 30 mm in distal pinnae), inarticulate, rounded adaxially or with two small crests, pulvini (1.5–)2.5–3.0 mm long, 3–5 mm in diameter at base (when dry, up to 12 mm when fresh). Pinnae opposite (rarely subopposite or alternate in a few leaves), 2–4(–5) on each side of the frond, 18–20 cm apart (closer towards apex), not overlapping. Basal pinnae similar to other pinnae, often curved backwards (basitropic) or perpendicular to the rachis. Middle pinnae 70 × 30 cm, oblong. Distal pinnae 52 × 25 cm, progressively reduced, ascendant towards apices (acrotropic), oblong. Terminal pinna absent (paripinnate) or similar to lateral pinnae (rarely). Secondary rachises terete, rounded adaxially, almost entirely winged, wings 1.0– 1.5 mm broad (on each side), plane, green, glabrous. Pinnules (of middle pinnae) shortly petiolulate or sessile. Secondary petiolules (0–) 2– 3 mm, articulate, rounded adaxially. Pinnules alternate, subopposite or opposite, (9–)14–16 on either side, 2.0– 3.5 cm apart, not overlapping. Basal pinnules similar to other pinnules or progressively and slightly reduced, curved backwards (basitropic), perpendicular to rachis or rarely ascendant towards apex (acrotropic), oblong, 8–11(–14) × 1.8–2.5 cm. Middle pinnules slightly ascendant towards apices (acrotropic), oblong, (11–)15–22 × 2.1–2.9 cm. Distal pinnules similar to other pinnules, ascendant towards apices (acrotropic), oblong. Terminal pinnule absent (paripinnate), similar to other pinnules or more developed than other pinnules (and often irregularly pinnate distally). Pinnule blades entire, bases obtuse, rounded or subtruncate, slightly asymmetrical (more acute on the distal side), shortly decurrent on the petiolules, margins serrate, glabrous, plane or slightly revolute, teeth 6 per cm, more developed towards the acumen, apex progressively acuminate, acumen 1.7–3.0 cm, somewhat to strongly discolorous, dark green or olive above, light green or glaucous below, sometimes reddish on developing leaves, coriaceous, glabrous. Venation pinnate, midveins reaching the apex, secondary veins distinct, undivided or furcate (at base or before midway to the margin), 2.2–2.5 mm apart, straight, slightly oblique, terminating in teeth apices, venuloids absent. Sori (1.0–)1.4–2.2 × 1.0 mm, widely set, 40–130 per pinnule, intramarginal and basal (often restricted to the basal half of the pinnule), at 1–2 mm from the leaf margin, not immersed or slightly immersed, oblong, more rarely elliptic, not indusiate. Sporangia 12–16 per sorus, fully fused into a synangium.

Representative specimens examined: — SEYCHELLES. Mahé: J. Stanley Gardiner s.n. ( K) ; Congo Rouge , 730 m, 30 May 2008, B. Senterre 5348 ( SEY) ; Congo Rouge Est , 820 m, 6 July 2011, B. Senterre & N. Labiche-Barreau 6126 ( SEY) ; Mont Cotton , 560 m, 17 July 2011, B. Senterre & I. Fabre 6141 ( SEY) ; Montagne Planneau (= Mont Harrison) , 628 m, 18 August 2013, B. Senterre 6593, 6594 ( SEY) ; Varigault , 576 m, 10 August 2011, B. Senterre & I. Fabre 6168 ( SEY) .

Distribution: —This species appears to be endemic to the island of Mahé in the granitic Seychelles, on the highest summits of the Morne Seychellois National Park and in the massif of Montagne Planneau. It has been searched for on Silhouette Island (close to Mont Dauban), but was not found there.

Ecology: —Usually as understory plant of the “tree fern lower montane forest belt” ( Elzein 2011, Senterre 2011), of evergreen rain forests, mostly above 750 m elevation. Due to telescoping effect this elevational belt would correspond to 1800–2500 m above sea level in continental areas or larger islands at similar latitudes. This elevational belt is characterized by the dominance of tropical montane forest species and tree ferns ( Cyatheaceae ). Ptisana laboudalloniana is occasionally found at lower elevations (> 500 m), but these are isolated individuals in wet ravines.

Conservation: —The geographical distribution pattern and population size of Ptisana laboudalloniana are very similar to those of Angiopteris chongsengiana , the two species being often found in association. Ptisana laboudalloniana is slightly more common (found in ca. 15 ravines, especially on the summits of Congo Rouge and Pérard) and each ravine contains slightly more mature individuals (ca. 20-30). Therefore, considering IUCN criterion D (very small population, IUCN 2011: 14, 58), this species can be classified as vulnerable (VU), i.e. less than 1000 mature individuals and area of occupancy less than 20 km ². The total number of mature individuals is estimated to ca. 300–500. The area of occupancy (AOO) and extent of occupancy (EOO) are respectively ca. 0.1– 0.2 km ² and 17 km ². All populations seemed very healthy, with abundant regeneration and little impact from the small populations of invasive species.

Etymology: —The specific epithet honours Seychellois botanist Mr. Victorin Laboudallon who contributed significantly to the botany, natural history and conservation of the Seychelles. Victorin Laboudallon is currently the chairman of a local NGO.

Vernacular name:—This species is rare in the Seychelles and has not been observed for a long time. If found, it was confused by local people with Angiopteris madagascariensis , which is superficially similar. Therefore it lacks a Creole vernacular name as yet. Due to its smaller size compared to the two other species of Marattiaceae in the Seychelles, we propose to name it ‘Pti baton monsenyer’.

Morphological affinities: —This species was first recorded on the Seychelles by Christensen (1912) as Marattia fraxinea , a species described from Mauritius and currently called Ptisana fraxinea var. fraxinea . Nevertheless, the Seychelles plants differ from typical P. fraxinea in being an exclusively montane species and having strongly winged secondary rachises. Another taxon with winged secondary rachises has been described from South Africa and is known as Ptisana fraxinea var. salicifolia . The latter taxon is larger than the Seychelles Ptisana (with leaves up to 3 m long), with laminae longer than the petioles and has at least 6 pairs of pinnae. Our molecular results show that Ptisana laboudalloniana is related to the rare species Ptisana purpurascens , endemic to Ascension Island, and that the South African Ptisana fraxinea var. salicifolia forms a distinct clade ( Fig. 1 View TABLE 1 View FIGURE 1 ). Ptisana purpurascens has slightly winged secondary rachises and leaves with few pairs of pinnae, but it differs from P. laboudalloniana especially in having thicker, fleshier and much shorter (4–10 cm) pinnule blades. In mainland Africa, we recognize another four species that all differ from the Seychelles species in having pinnules with abruptly caudate-acuminate apices combined with the secondary rachises not being winged: Ptisana odontosora (endemic to Guinea), P. robusta (endemic to São Tomé) and two undescribed species (one being commonly found from Cameroon to Gabon and the second found from Guinea to tropical East Africa).