Tridactyle minutifolia Stévart

D’Haijere, Tania, Leguil, Sophie, Meerts, Pierre & Stevart, Tariq, 2015, Taxonomy of Atlantic Central African orchids 4. A new species of Tridactyle (Vandeae, Epidendroideae, Orchidaceae) from Gabon and Equatorial Guinea, Phytotaxa 212 (2), pp. 141-148 : 143-145

Tridactyle minutifolia Stévart & D’haijère, sp. nov. Fig 1 A–K

Tridactyle minutifolia Stévart & D’haijère is close to T. tridactylites and to Tridactyle lisowskii ( Szlachetko 1994: 547) Szlachetko & Olszewski (2001: 716) but it differs from the former by its erect habit and linear, thinner leaves and from the latter by its epiphytic habit and linear, more distant, leaves. It is also close to Tridactyle stevartiana Geerinck in Delepierre & Lebel (2001: 7) from which it differs by having an erect habit, much longer inflorescences and side lobes of the labellum denticulate.

Type:— GABON. Monts de Cristal, SEEF logging concession, 490 m, 0.2542° N, 10.3021° E, 26 October 2011, Stévart, Niangadouma, Akouangou & Kaparadi 3609 (holotype: BRLU!, isotype: LBV, MO).

Epiphytic herb with unbranched erect stem, 20–40 cm long and 2 mm in diameter, internodes 2–4 mm long, brownish to black spots. Roots up to 0.5 mm in diameter, glabrous. Leaves distichous; blade linear, 5–7 × 0.2–0.4 cm, glabrous, dull, green; apex unequally bilobate. Inflorescences up to 8 per shoot, opposite to the leaf, semi-pendulous, 3.5–5.5 cm long, 7–10 flowered. Floral bracts broadly triangular, apex acute, 1.5–2 × 1–1.5 mm. Flowers arranged in two rows, 2–4 mm spaced out, white-yellowish to orange. Pedicel and ovary 3–4 × 1 mm, papillose. Sepals ovate, acute to acuminate, 3–5 × 1–2 mm, adaxially 3-veined, the tips recurved, margins entire, glabrous. Petals linear, acute, 3–5 × 1 mm, margins entire or slightly dentate, glabrous. Labellum auriculate at the base, auricules ronded, 0.5–1 mm diameter; labellum trilobate to about half way, 5 × 1.3 mm, glabrous; mid-lobe 2.5–4 mm long, triangular; side lobes longer, spreading, almost threadlike. Spur mostly absent, or if present, 7–8 mm long, cylindrical, straight, apex acute. Flower scent not observed.

Additional specimens examined: — EQUATORIAL GUINEA, Rio Muni, Monte Mitra , 1.383° S, 9.966° E, Stévart 823 ( BRLU!) . GABON, Ogooué-Maritime, Doudou Montains, West of Doussala, Réserve de la Faune de Moukalaba , 350 m, 2.15° S, 10.20° E, 1988, Arends 829 ( WAG!) ; ibid., 26 May 1988, Arends 870 ( WAG!) ; ibid., 5 December 1984, Arends & de Wilde 634 ( WAG!) ; ibid., 1985, Van der Laan 841 ( WAG!) ; Tchimbélé , 0.2212° N, 10.1236° E, Biteau 155 ( BRLU!) ; ibid. GB 416 ( BRLU!) ; Moyen-Ogooue, Ndjolé area. Concession Bordamur , SE of Ndjolé, between Wata NP and La Lopé NP, bottom of a very wet valley, 570 m, 0.1043° S, 10.4553° E, 25 February 2009, Stévart, Dauby, Nguema, Mounoumoulossi & Bissiemou 3054 ( BRLU!) .

Distribution:— Endemic to Gabon and Equatorial Guinea. The distribution range of Tridactyle minutifolia is comprised in the Atlantic Sector of the Lower Guinea Domain ( Senterre 2005), which is the coastal part of the Lower Guinea Domain of the Guineo-Congolian Region ( White 1979).

Habitat and Ecology:— Epiphytic herb found in high canopy and dense rainforest with many Burseraceae , sometimes exploited. It was found as an epiphyte on Bikinia letestui ( Pellegrin 1942: 120) Wieringa in Wieringa & van der Maesen (1999: 222) between 25 and 40 m in the canopy (e.g. specimen Stévart 3054). The altitude range of the species was estimated to be between 350 and 490 m (for specimens with spur) and around 570 m (for specimens without spur).

Phenology: —Flowering in February, May and between October and December.

Plants in Cultivation: —A specimen of Tridactyle minutifolia (J.C. Arends, A.M. Louis & J.J.F.E. de Wilde 634) was grown at the Wageningen Herbarium shadehouse (1984PTGA309). Two others are currently in cultivation in Libreville, one in the Garden of J.P. Biteau in Libreville (GB 252) and one in the Sibang shadehouse (GB 416). The plant growing at Wageningen has produced four specimens (Arends 634, Arends 829, Arends 870 and Van der Laan 841) and the plants from Libreville have produced two specimens (Biteau 155 and GB 416).

Conservation Status:— IUCN red list category: endangered [EN B2ab(i,ii,iii,iv,v)]. The EOO of Tridactyle minutifolia is estimated to be 14,920 km 2 and its AOO is about 20 km 2, the second of which falls within the limits for endangered status under criterion B. Tridactyle minutifolia is known from five subpopulations, one in Equatorial Guinea and four in Gabon: one in Tchimbélé in the Monts de Cristal National Park, one in the Mont Doudou and two in logging concessions (SEEF and Bordamur). These five subpopulations represent a total of five locations, and thus Tridactyle minutifolia qualifies for endangered status under criterion B2a. The main threat to the species is deforestation for logging, including trees on which the orchid grows. This is a result from a strong demand for timber in Europe and Asia, a pressure which we anticipate will continue in the future. The projected ongoing loss of its habitat allows to predict a continuous decline of the number of subpopulations and mature individuals, and thus also of its AOO and EOO.

Figures

FIGURE 1. Tridactyle minutifolia A. Habit. B, C. Flower, side and face views. D. Dorsal sepal. E. Lateral sepal. F. Petal. G. Lip. H, I. Column with anther and anther cap, front and side view. J. Column with anther cap opened. K. Viscidia and tegula. Drawn from holotype Stévart 3609 by Hans de Vries.