Polystachya orophila Stévart & E.Bidault, 2016

Bidault, Ehoarn, Lowry Ii, Porter P. & Stévart, Tariq, 2016, Polystachya orophila (Orchidaceae, Polystachynae), a new species from tropical West Africa, and clarification on the nomenclature and taxonomy of P. microbambusa, Phytotaxa 260 (3), pp. 247-257 : 250-254

Polystachya orophila Stévart & E.Bidault sp. nov. ( Fig. 1 , 3 )

Polystachya orophila Stévart & E.Bidault sp. nov. resembles Polystachya microbambusa by its flowers, similar in all features, but differs by its type of growth: P. orophila has pseudobulbs emerging aside one another, forming clusters of pseudobulbs, placing it in section Polystachya , whereas P. microbambusa has pseudobulbs successively emerging one on top of another, forming a well-developed, perennial stem, placing it in the monotypic section Dimorphocaules .

Type:— GUINEA. Monts Nimba, site du patrimoine mondial, crête principale au sud de la concession minière SMFG, savane d’altitude, crêtes rocheuses. 7°39’17’’ N, 8°22’57’’O, 923 m, 1 July 2012 (fl), E. Bidault & M. Diabaté 675 (holotype MO!, isotypes BR!, P!, SERG!, WAG!).

Polystachya cyperacearum Chevalier (1920: 616) , nom. nud.

Stems caulescent, pseudobulbous at base, then narrowly cylindrical above. Pseudobulbs 0.7–2.3 cm long, 0.4–0.8 cm in diameter, narrowly cylindrical, erect, 4–11 leaved. New pseudobulbs arise from aside of the preceding one, forming clusters of new and old remaining pseudobulbs. Leaves up to 18 (21) × 0.3–0.8 (1.4) cm, linear to very narrowly ovate, gradually tapering towards the acute apex. Inflorescence erect, a lax raceme, 2–9 (11)-flowered; peduncle and rachis pubescent. Flowers medium-sized, bright yellow. Floral bracts 7–8 mm long, ovate, thin, glabrous, apex acute to acuminate. Pedicel and ovary 6–10 mm long, slender, rather densely pubescent. Dorsal sepal 10–12 × 3.5–4.5 mm, 2.5 mm wide at base, very narrowly triangular to linear, thin, with two lateral attenuated lobes at 0.5 mm from the base, sparsely pubescent outside, 3-veined, the two lateral ones each dividing into two at 1 mm from the base, apex acuminate. Lateral sepals 10–13 × 5 mm at base, narrowly triangular, thin, asymmetrical, with a 1 mm high keel on the outside along the mid-vein, sparsely pubescent outside along the keel, 3-veined, the two lateral ones each dividing into two at 1 mm from the base, the mid-vein starts shifted from the centre, towards the lower side of the sepal, apex acuminate. Mentum 2.5–5 mm long, broadly saccate. Petals 9–10 × 2–3 mm, linear, thin, pubescent at base, 3-veined, apex acuminate. Lip 10–12 × 5–7 mm, rather sparsely pubescent in the centre, with linear-oblong, minutely papillate callus 3 mm long in the lower third, rather obscurely 3-lobed just below the middle, shortly clawed, claw 2 × 1.2–1.9 mm, broadly ovate; lateral lobes 3–5 × 1.5–2.5 mm, rhombic or ovate-triangular, thin, apex acute; middle lobe 5–7 × 2–3.5 mm, triangular, fleshy, with margins rolled inside, apex acute. Column short and massive, column foot 6 mm long.

Distribution & ecology:— Polystachya orophila is known from Guinea (Nimba Mountains and the Simandou range) and the Loma Mountains in Sierra Leone. It occurs from an elevation of 900 m on Nimba to the summit of Mount Bintumane in the Loma Mountains at 1,800 m. As the Nimba range spans three countries, Guinea, Ivory Coast and Liberia, P. orophila can be expected to occur in the latter two as well. It is exclusively known from montane savannah on rocky outcrops emerging from the surrounding savannah, where it grows as a lithophyte, although it can also be an epiphyte growing on root clusters of Afrotrilepis pilosa , which provides protection from fires.

Conservation status:—The IUCN Red List category is endangered [EN B2ab(i,ii,iii,iv,v)]. The EOO of Polystachya orophila is estimated to be 9,891 km 2, which falls within the limits for Vulnerable status under criterion B, and its AOO is estimated at about 28 km 2, which is within the limits for Endangered status, likewise under criterion B. This species is restricted to the upper parts of isolated mountain ranges in Guinea and Sierra Leone, and its distribution is thus extremely fragmented. Polystachya orophila is known from thirteen subpopulations, four of which are encompassed within legally protected areas (one in the Loma Mountains Forest Reserve, and three in the Nimba Mountains World Heritage Site). These thirteen subpopulations represent a total of four locations, below the threshold for Endangered status under criterion B2a. Since the species is resistant to the frequent human-caused fires that regularly affect the sites where it occurs, the main threat it may face is habitat destruction due to road construction associated with the ongoing exploration phase of mining projects at both Simandou and Nimba. Moreover, a decision to proceed with the planned mining activities would significantly increase the scope and intensity of impacts at both sites, thereby resulting in a higher level of threat. While a decision to begin exploitation is currently on hold at both sites, such projected exploitation would result in loss of its habitat, which leads us to predict a continuous decline in the quality of its habitat, as well as of the number of subpopulations and mature individuals, and thus, also of its AOO.

Additional specimens examined:— GUINEA. Nzérékoré (Mt Nimba), 13 April 1949, Adam 4880 ( P) ; Nzérékoré , Nimba, February 1965, Adam 20881 (K) ; Monts Nimba , site du patrimoine mondial, crête principale au sud de la concession minière SMFG, savane d’altitude, crêtes rocheuses, 1 July 2012, Bidault & Diabaté 683 ( BR, MO, P, SERG, WAG) ; Monts Nimba. Concession minière SMFG. Haute vallée de Zougué, 29 June 2012, D. Bilivogui, Nielsen & Mas 153 ( BR, MO, P, SERG, WAG) ; Nzérékoré , Macenta , Simandou Range, ridge descending from the main range to the west, Plot M5, 3 July 2010, van der Burgt & Cheek 827 (K, WAG) ; Pays des Guerzés , Montagne de N’Zo, 26 March 1909, Chevalier 21007 ( P) ; Pays des Guerzés , Montagne de N’Zo, 28 March 1909, Chevalier 21037 (K, P, WAG) ; Nzérékoré , Nimba Mountains, Pierre Richeaud, 26 March 2009, Haba, Bilivogui & Traoré 152 ( WAG) ; Nzérékoré , Nimba Mountains, mountain-slope between camp and ridge, 25 June 2007, Jongkind, Holié & Cherif 7837 ( P, MA, BR, G, K, MO, WAG) ; Nzérékoré ; Nimba Mountains , east slope of range, above Vallée de Wolanda, 16 June 2007, Jongkind, Holié & Cherif 7688 ( BR, P, WAG) ; Nimba mountains , north end of main ridge, open rocky area in grassland with trees and shrubs, 2 July 2012, Jongkind, Bilivogui & Mas 11356 ( BR, MO, P, SERG, WAG) ; Guinée Forestière , les Monts Nimba, à la limite de la concession minière SMFG et de la zone du patrimoine mondial, partie supérieure de la vallée du Wolanda, savane d’altitude, 20 February 2012, Mas, Diabaté & Bidault 1255 ( MO, SERG) ; Monts Nimba , concession minière SMFG, Château et amonts de la rivière Zougué (amont de la station de pompage), dans les rochers plus ou moins lamellaires d’une crête rocheuse en savane d’altitude, 29 June 2012, Mas, Nielsen & Bilivogui 1292 ( MO, SERG) ; Monts Nimba , partie N.E., 1600 m, February 1942, Schnell 323 ( P, MO, WAG, K) ; Monts Nimba [crêtes du Nimba NE], April 1942, Schnell 1170 ( P) ; Monts Nimba , June 1945, Schnell 3018 ( P) ; Mont Nimba , between base pédologique et Wolanda River, in savannah, 23 June 2012, Stévart, Serein & Traoré 4050 ( BRLU) ; Mont Nimba , between base pédologique et Wolanda River, in savannah, 23 June 2012, Stévart, Serein & Traoré 4052 ( BRLU) ; Mont Nimba , between base pédologique et Wolanda River, in savannah, 23 June 2012, Stévart, Serein & Traoré 4054 ( BRLU) ; Guinée Forestière , Nimba Mountains, SMFG iron ore mine concession, station météorologique de Château, on rocky outcrops, 5 October 2011, Stévart, Bidault, Diabaté & Bilivogui 4065 ( MO) ; Guinée Forestière , Nimba Mountains , SMFG iron ore mine concession, savannah in Château near Station Meteo 1, edaphic savannah, 5 October 2011, Stévart, Bidault, Diabaté & Bilivogui 4072 ( MO) ; Mont Nimba , between base technique and base géologique, near the zigzag, in savannah, 1 July 2012, Stévart & Serein 4576 ( BRLU, MO) ; Mont Nimba , Pierre Richard, in burnt savannah, 1 July 2012, Stévart & Serein 4577 ( BRLU) . SIERRA LEONE. Bintumane , Monts Loma, November 1944, Jaeger 382 ( P) ; Pente N.E. du Pic Bintumane, 14 August 1945, Jaeger 977 ( P) ; Sommet du Bintumane, Mts. Loma , 17 August 1945, Jaeger 1046 (K, P) ; Sommet du Bintumane, Mts. Loma , 17 August 1945, Jaeger 1047 ( P) ; Mts. Loma , 29 July 1964, Jaeger 6918’ ( P) .

Etymology:— The epithet ‘ orophila ’ refers to the high montane savannah habitat of this orchid.

Figures

FIGURE 1. Polystachya orophila: A. Entire flowering plant, growing as an epiphyte on Afrotrilepis pilosa root clusters (Bidault 675). B. Entire plant, growing as a lithophyte (Stévart 4065). C. Detail of the base of the plant, showing lateral growth of the pseudobulbs (Stévart 4072). D. Detail of the flower (Bidault 683). All pictures by E. Bidault.

FIGURE 3. Polystachya orophila.A. Habit; B. Flower; C. Flower, opened; D. Flower, frontal view, opened; E. Labellum; F. Lateral sepal; G. Petal; H. Dorsal sepal; I. Ovary and column; J. Column, side view; K. Column, frontal view; L. Column, from above; M. Anther-cap; N. Pollinium. A, from Jongkind et al. 7837; B–D, from Stévart et al. 4550; E–N, from Stévart et al. 4554.