Gastrodia madagascariensis H.Perrier ex Martos & Bytebier, 2015

Martos, Florent, Johnson, Steven D. & Bytebier, Benny, 2015, Gastrodia madagascariensis (Gastrodieae, Orchidaceae): from an historical designation to a description of a new species from Madagascar, Phytotaxa 221 (1), pp. 48-56 : 49-52

Gastrodia madagascariensis H.Perrier ex Martos & Bytebier , sp. nov. ( Figs 1–2 )

TYPE:— MADAGASCAR. Toamasina: Manompana village, Ambodiriana Forest , elev. 145 m, 16°40’21.30”S, 49°42’8.52”E, 16 August 2013, Martos 906 (holotype NU (spirit)!, isotype TAN!).

Diagnosis: — Similar to Gastrodia similis Bosser (2006: 52) , from which it can be distinguished by the perianth tube spreading towards the apex, the cordate stigma, and the emerald green lip colour.

Slender, leafless, achlorophyllous herb. Rhizome subterranean, fleshy, fusiform, villose to tomentose, 20–50 × 3–7 mm, densely noded; adventitious roots up to 300 × 1 mm. Peduncle erect, 100–300 mm tall, glabrous, dark brown to blackish, with 3–4 tubular sheaths in the lower half; sheaths 3–6 mm long, truncate and with an abrupt acumen 3–4 mm long. Inflorescence racemose, with (1–)3–12 flowers, rachis 10–40 mm long; bracts lanceolate to ovate, acute, 6 × 3 mm. Pedicel slender, twisted, 5–8 mm long. Flowers resupinate, campanulate, spreading; sepals and petals dull brown adaxially, light brown or reddish brown abaxially, blackish brown at apex; lip yellow-orange, tinged with emerald green at apex; two tubercular processes borne on the column-foot emerald green. Sepals fleshy, ovate, obtuse, 12–14 × 7–9 mm, connate for about two thirds of their length except between the lateral sepals where the fusion only reaches halfway, verrucose adaxially, wrinkled abaxially. Petals slightly fleshy, broadly ovate, obtuse, 5–6 × 3–4 mm, adnate to the sepals and forming a floral tube together with them. Lip inserted at the apex of the column-foot, free from other perianth parts, completely enclosed within perianth tube, fleshy, broadly ovate, 7–8 × 3–4 mm, broadly acuminate, papillose; base shortly clawed; margin ascending on the sides; adaxial side transversely wrinkled and bearing two apical incurved ridges which are somewhat V-shaped, the tip of the V lengthening towards the front; abaxial side canaliculate. Column elongate, 6–7 mm tall, narrowed at base, winged distally, with a tooth-like appendage on either side of the column at apex; foot incurved, with a pair of cephaloid tubercular processes at apex; anther subcircular, ± 1.2 × 0.4 mm, broadly rounded at the front; pollinia 2, granular, composed of friable massulae, attached to a shared viscidium; stigma borne on a raised projection at base, cordate. Ovary trigonous, obconical, ± 5 mm long. Capsule erect, ovoid, ± 25 × 5 mm, borne on a pedicel elongating up to 40 cm during fruit maturation.

Distribution and habitat:— Gastrodia madagascariensis is only known from Ambodiriana Forest near Manompana ( Fig. 3 ). Here, it grows in evergreen, humid forest below 200 m and is more commonly found in the vicinity of the river Manompana and its tributaries.

Conservation:— Since 1996, Ambodiriana Forest is protected by a non-governmental organisation, namely the Association de Défense de la Forêt d’Ambodiriana (ADEFA). However, slash-and-burn deforestation is common along this part of the coast of Madagascar, and Ambodiriana Forest is situated less than two km away from the nearest rice fields and seven km from Manompana village. In addition, the fact that the Gastrodia orchids require specific mycorrhizal associations for carbon uptake throughout their life cycle ( Martos et al. 2009, Selosse et al. 2010, Selosse & Martos 2014) renders them extremely vulnerable to habitat disturbance. In August 2013, less than 50 flowering plants were seen throughout Ambodiriana Forest, covering an area of approximately 2.25 km 2 and we are at present not aware of any other locality where this species persists. Therefore, G. madagascariensis is considered “Critically Endangered” according to the IUCN Red List Categories and Criteria ( IUCN 2014).

Etymology:— The epithet madagascariensis refers to Madagascar, where this species is endemic.

Phenology:— Gastrodia madagascariensis flowers during the cooler, drier season between July and August. Fruiting occurs from August and throughout September.

Other specimens examined:— MADAGASCAR. Toamasina: Fandrarazana River basin ( N. E.), elev. 200 m, September 1912, Perrier de la Bâthie 11349 ( P [barcode P00540570 ] digital image!) (in fruit stage) .

Figures

FIGURE 1. Gastrodia madagascariensis. A. Habit; note the dark color of the peduncle contrasting with the whitish pedicels, and the dark colour of the perianth tube at the apex. B. Open flower, front view; note the perianth tube spreading towards the apex, and the reddish brown (bottom half) and light brown (top half) colour of the perianth tube on the inner surface.C. Open flower, three quarter view; note the emerald green colour of the lip tip and of two tubercular calli borne on the column-foot (also seen on B). D. Dehiscent capsules borne on elongated fruiting pedicels. E. Fusiform rhizome with fine adventitious roots. Photographs:A.Charbouillot (A–C) and J.-M.Hervouet (D).

FIGURE 2. Gastrodia madagascariensis. A. Habit (inflorescence with rhizome). B Detail of rhizome. C. Detail of inflorescence. D. Elongating pedicel. E. Open flower, front view. F. Sepals and petals flattened. G. Pedicel, ovary, column and lip, side view.H. Lip (adaxial) and base of column. I. Lip (abaxial). J. Lip (abaxial) appressed to column. K. Column (adaxial). L. Detail of column apex without anther cap. M. Detail of column apex with anther cap. N. Fruits. O. Pollinia.A–C, E–M from Martos 906; D, N, O from photographs. Scale bars: A, 10 mm; B–C, E–F, N, 5 mm; D, 50 mm; G–L, 1 mm; M, O, 0.5 mm. Drawn by A.J.Beaumont.

FIGURE 3. Map of Madagascar showing the distribution of the various observations of Gastrodieae on the island. Didymoplexis avaratraensis and D. recurvata, both endemic to Madagascar, co-occur in the northern province of Antsiranana, in evergreen wet forest at mid elevation (Cribb et al. 2013). Didymoplexis verrucosa, also known from South Africa, was recently photographed in the western province of Mahajanga, in deciduous seasonally dry forest (Cribb et al. 2011). Gastrodia madagascariensis occurs in the eastern province of Toamasina opposite the island Nosy Boraha, in evergreen wet forest at low elevation. Filled triangles: flowers observed. Open triangle: only fruits observed.