Didymoplexis recurvata P. J. Cribb, Nusb. & L. Gaut.,, 2013

Cribb, Phillip, Gautier, Laurent & Nusbaumer, Louis, 2013, How many species are there in the holomycotrophic genus Didymoplexis Griff. (Orchidaceae) in Madagascar?, Candollea 68 (1), pp. 41-49 : 44-45

Didymoplexis recurvata P. J. Cribb, Nusb. & L. Gaut., spec. nova

( Fig. 1 , 4 ).

Typus: MADAGASCAR. Prov. Diego-Suarez/ Antsiranana: sous-préfecture de Vohemar, commune rurale de Daraina, forêt de Binara , 13°15’S 49°37’E, fl., 985 m, 12.XII.2005, Nusbaumer & Ranirison 1763 bis (holo-: G [ G00181978 ]! ; iso-: TAN!, research herbarium of Daraina).

AffinisDidymoplexisavaratraensissed floribius albisvel roseis, sepalis petalisque latioribus, sepalis lateralibus tertiobasali adnatis, labello late obovato emarginato, callo elongato ad apicem trilobato et brachiisdolabriformibus pendentibus ad apicem columnae satis distinguenda.

Holomycotrophic herb up to 10 cm tall, growing from a subterranean elongated blackish tuberous rhizome. Leaves scale like, very small. Inflorescence erect, racemose, laxly up to 6- flowered, the flowers opening one at a time and successively; peduncle slender, erect, bearing a small ovate bract below inflorescence, white; rachis terete, slender; pedicel with longitudinal ridges; bracts ovate, acute, 1.5-2 mm long. Flowers with white sepals and petals and a white to rose-pink lip with a yellow callus, the column buff flushed. Dorsal sepal erect, lanceolate, subacute, 7-8 × 4-5 mm; lateral sepals adnate in basal third, ovate, rounded to subacute, 7-8 × 4-5 mm. Petals oblanceolate, acute, 7-8 × 5-7.5 mm, adnate in basal third to the sepals. Lip shortly narrowly clawed at base, very broadly obovate-spatulate, emarginate, 3.5-4 × 5-6 mm, slightly decurved at apex; callus on claw erect, dilated and 3-lobed at tip. Column 3.5-5 mm long, slender at base, strongly winged at apex, the wings dependent, recurved, rounded at tip, 1 mm long. Fruit unknown.

Etymology. – The specific epithet refers to the column with recurved apical arms bilobed at the tips.

Distribution. – The species is only known from the Binara forests in the Loky-Manambato (Daraina) region, in Antsiranana Province in North-East Madagascar. Only 15- 20 individuals were observed in one population in the Loky-Manambato region among the 54,000 plant occurrences recorded during the Loky-Manambato vegetation study ( NUSBAUMER, 2011).

Habitat and ecology. – Didymoplexis recurvata was recorded in evergreen montane forest on metamorphic rock; at 985 m. This terrestrial herb occurs in forests with canopies reaching 11 to 15 m, emergent trees reaching 21 to 24 m and with a second aborescent stratum at 8 to 10 m, with two woody strata at 5 to 7 m and at 1 to 2 m high, and with a no herbaceous strata, the soil densely covered with dry leaves of trees.

The most frequent species recorded together with D. recurvata in Loky-Manambato vegetation surveys include, in decreasing abundance: Marojejya insignis Humbert , Ravenea sambiranensis Jum. & H. Perrier , Dypsis nodifera Mart., Weinmanniadecora Tul. , Syzygium condensatum (Baker) Labat & G. E. Schatz , Plagioscyphus aff. louvelii Danguy & Choux and Blechnum attenuatum (Sw.) Mett. var. attenuatum .

Flowering time. – December.

Conservation Status. – With only one small subpopulation, included in the Loky-Manambato protected area, Didymoplexis recurvata is assigned a preliminary status of “Critically Endangered” (CR D) following the IUCN Red List Categories and Criteria ( IUCN, 2012).

Notes. – Didymoplexis recurvata is clearly distinguished from the other African and Malagasy species of Didymoplexis known in flower by its column which has short recurved apical arms that are bilobed at the tips, as well as by its lip which lacks rows of warts but has at the base a tall apically trilobed entire callus and by its sepals and petals that are adnate in the basal third.

Figures

Fig. 1. – Didymoplexis avaratraensis P. J. Cribb, Nusb. & L. Gaut. A. Habit; B, C. Flower, side view; D. Dorsal sepal abaxial view; E. Lateral sepals, front view; F. Lip (labellum), flattened, front view; G. Labellum and column details, front view; H. Flower, front view. Didymoplexis recurvata P. J. Cribb, Nusb. & L. Gaut. I. Flower, front view; J. Lip (labellum), flattened, front view. [A-H: Nusbaumer & Ranirison1763, G; I-J: Nusbaumer & Ranirison 1763bis, G] [Drawing: Juliet Beentje]

Fig. 4. – Didymoplexis recurvata P. J. Cribb, Nusb. & L. Gaut. A. Flower, front view; B. Flower from below, bud and pedicel. [Nusbaumer & Ranirison 1763bis] [Photos: L. Nusbaumer,12.XII.2005]