Angraecum baiderae Pailler, 2020

Pailler, Thierry, Verlynde, Simon, Bytebier, Benny, Florens, F. B. Vincent & Baider, Cláudia, 2020, Revision of Angraecum sect. Perrierangraecum (Orchidaceae; Epidendroideae; Vandeae) for the Mascarenes, with a description of a new endemic species for Mauritius, Phytotaxa 442 (3), pp. 183-195 : 185-187

1. Angraecum baiderae Pailler , sp. nov. ( Figs. 1 , 2E )

Type:— MAURITIUS. Macchabé, 650 m elev., 24 May 2019, fl., fr., Baider CB 2791 (holotype MAU 0029132!, spirit).

Diagnosis:— Angraecum baiderae is close to Angraecum borbonicum Bosser (1988: 20) , from which it differs by its smaller size (plants being nearly half the size of the latter), narrower leaves, and by the shape of its labellum, which is broadly obovate with apiculate apex (vs ovate with acuminate apex). It differs from A. rutenbergianum Kraenzlin (1882: 257) by having a shorter peduncle (3–8 mm vs 20–25 mm) and sepals (12–21 mm vs 20–37 mm long), a smaller labellum (14–23 × 11–15 mm vs 30–35 × 17–18 mm), which is also of a different shape (broadly obovate vs rhombicelliptic), and smaller capsule (10–19 × 5–12 mm vs 20–27 x 10–11 mm).

Description:— Plants epiphytic, erect; acaulous or stem single, 5–6(–10) mm long, covered with old leaf sheaths; leaf sheaths closely imbricate, keeled at back, wrinkled when dry; internodes 0.3–0.7 mm. Roots many, thin, smooth. Leaves 3–5, erect, (15)–25(–80) × 3–5 mm, oblong or narrowly-oblong, coriaceous, green, V-shaped in cross-section at base; base narrow, flat towards round apex; apex unequally bilobed, margins smooth. Inflorescence 1(–2), single-flowered. Peduncle 3–8 mm, covered by 3–5 membranous sheaths, 6–7 mm long, light brown, imbricated; upper sheath keeled. Floral bracts 4–5 mm long, ovate, obtuse and sometimes cuspidate at apex, same texture as leaves. Flower resupinate, 20–25 mm diameter, white, fleshy, fully opening, faintly scented. Sepals (12–)17–21 × 2.5–3.5 mm at base, lanceolate, acute, 7(–9)-veined; median sepal slightly shorter than the laterals, 7-veined. Petals (12–)17–20 × 1.5–2.5 mm at base, narrowly lanceolate, 3–5-veined. Labellum 14–23 × 11–15 mm, broadly obovate, rounded at base, larger at upper third of its length; apex apiculate to long-apiculate, without median keel, multiveined. Spur 50–80 mm long, filiform, more or less curved, sometimes making a loop at base of flower. Column 1.0– 1.5 mm high, fleshy; auricles rectangular, 0.6 mm wide, obliquely erect. Anther cap 2 mm diameter, opercular, keel gibbous and fleshy, not easily detaching. Rostellum abnormally developed. Pollinia in direct contact with stigma (autogamy). Ovary 12–15 mm long, pedicellate, narrowed at the base; triangulate. Capsule erect, triquetrous, with 3 slightly marked intermediate ribs, 10–19 × 5–12 mm, long-lasting; peduncle 3–5 mm long.

Distribution:— Mauritius.

Habitat and ecology:— Epiphytic in humid tropical forest.

Conservation status:— Apart from the localities known from herbarium specimens, the species also occurs in Brise Fer forest, all being within the Black River Gorges National Park, Mauritius ( Fig. 3A ). In a quantitative ecological study in Brise Fer ( Mawlah 2007), the species was absent from samples within native forest highly invaded by alien plants, mainly Psidium cattleyanum Sabine (1821: 317) ( Myrtaceae , following the nomenclatural note of Tuler et al. 2018). In contrast in adjacent similar forest areas where invasive alien plants were removed about a decade previously, a recovering population (50% juveniles, 50% adults) was found. Quantitative line transects detected this species only at the edges (e.g. along forest tracks) of invaded forest in a density about 10 times lower than in the adjacent forest that was cleared of invasive alien plants ( Mawlah 2007). In the region of Macchabé and Pétrin, most plants seen were also found along the edges of the track, with the latter site having individuals inside areas cleared of invasive plants. The known Area of Occupancy is 20 km 2, and its Extent of Occurrence is 34 km 2. Given its limited distribution (two localities using ConR version 1.2.4) and the fact that the overwhelming majority of its habitat is sustaining increasing invasions by alien plants ( Florens et al. 2016) and losing native host trees (a halving in 68 years) even within protected areas ( Florens et al. 2017), resulting in on-going degradation of habitat and inferred loss of mature individuals, the species should be considered as Endangered (EN B1ab(iii,v)+B2(a b(iii,v)).

Phenology:— Flowering in April and May (with one specimen in September), fruiting from April to September.

Etymology:— This species is dedicated to Dr. Cláudia Baider, curator of The Mauritius Herbarium (MAU), who collected the type specimen.

Additional specimens examined (paratypes):— MAURITIUS. Bassin Blanc , 13 April 1974, fl., fr., Bosser 21859 ( P00754507 ) ; 28 April 1978, fl., fr., Bosser 22439 ( P00754508 ) ; Bel Ombre , 20 April 1974, fr., Bosser 21910 ( P00754509 ) ; 8 June 1976, fr., Bosser 22273 ( P00754506 ) ; Florin , 4 April 2006, fl., Sevathian s.n. ( MAU 0001997 , spirit) ; Plaine Champagne , 3 June 1976, fr., Bosser 22267 ( P00754510 ) ; Pétrin , 28 April 1965, fl., fr., Lalouette s.n. ( MAU11993 ) ; 17 September 2009, outside Conservation Management Area , fl., fr., Pynee s.n. ( MAU 0001980 ; MAU 0001981 , spirit) ; Conservation Management Area , 650 m, 29 June 2019, fr., Baider & V. Florens CB 2814 ( MAU 0029133 ) .

Figures

FIGURE 1. Angraecum baiderae Pailler sp. nov. A. Flowering specimen, also showing leaves and roots. B. Fruiting specimen, showing sheaths. C. Lateral sepal. D. Median sepal. E. Petal. F. Labellum. G. Side view of the column. H. Side view of the anther cap. I. Front view of the anther cap. J. Cross-section of the ovary. Drawing by Françoise Crozier.

FIGURE 2. Angraecum sect. Perrierangraecum of the Mascarenes.A. Angraecum cucullatum. B. Angraecum liliodorum. C. Angraecum cornigerum. D. Angraecum borbonicum. E. Angraecum baiderae. Photos: A, C, D. Frederic Henze; B. François Vandeschricke; E. F.B. Vincent Florens.

FIGURE 3. Distribution of the five species of Angraecum sect. Perrierangraecum on the islands of the Mascarenes. A. Angraecum baiderae (Mauritius). B. Angraecum borbonicum (Réunion). C. Angraecum cucullatum (Réunion). D. Angraecum cucullatum (Mauritius). E. Angraecum cornigerum (Réunion). F. Angraecum liliodorum (Réunion).