Angraecum darainense P. J. Cribb & Nusb., 2012

Cribb, Phillip, Nusbaumer, Louis & Gautier, Laurent, 2012, Angraecum darainense P. J. Cribb & Nusb. and Aeranthes unciformis P. J. Cribb & Nusb. (Orchidaceae), two new species from northern Madagascar, Candollea 67 (2), pp. 269-275 : 270-272

Angraecum darainense P. J. Cribb & Nusb. , spec. nova

( Fig. 1 & 2 ).

Typus: M ADAGASCAR: province de Diego-Suarez/Antsiranana, sous-préfecture de Vohemar, commune rurale de Daraina , forêt de Bobankora, partie nord , 13°13’S 49°46’E, 535 m, fl., 26.I.2005, L.Nusbaumer & P.Ranirison 1430 (holo-: G!; iso-: P, herbarium of Daraina).

AffinisA.melanostictosed caulibus longioribus, foliis densioredispositis, vaginisfoliorum emaculatiset calcari floris 8-10 cm longo (nec tantum 7 cm) satis differt.

A slender scrambling prostrate lithophytic herb with a stem up to 22 or more cm long; roots adventitious, slender, 1 mm in diam. Leaves fleshy, distichous, twisted at the base to lie in one plane, linear-oblong, obtusely obliquely bilobed at the tip mostly with a longer proximal lobe and a shorter distal lobe, of unequal length, 5-11 1-2 mm; unspotted leaf sheaths. Inflorescences axillary, 1-flowered; peduncle terete, slender, 6 mm long; bracts very small, ovate-triangular, acute, up to 2 mm long. Flower resupinate, large for the size of the plant, white; pedicel and ovary 20 mm long. Dorsal sepal erect, somewhat concave, lanceolate, acute, 9 2.5 mm; lateral sepals decurved, falcate, oblonglanceolate, acute, 10-11 3 mm. Petals porrect, narrowly lanceolate, acute, lying each side of the column, 8.5-9 2.5 mm. Lip somewhat deflexed, concave, lanceolate, acute, 10 2.4 mm; spur pendent, somewhat sigmoid-sinuate, narrowly cylindrical, tapering in apical half, 80-100 mm long. Column 2 mm long; anther cap broadly obovoid with an erose apical margin.

Notes. – Angraecum darainense , described here, is allied to A.melanostictum Schltr. (sect. Pseudojumellea Schltr. ), a species described from the Marojejy Massif, 140 km to the south of Daraina. The new species differs in having a flower with a longer spur, 8-10 cm long, more densely arranged leaves on the longer stems, unspotted leaf sheaths, and a much shorter and narrower leaf blade.

Distribution. – The species is only known from the Bobankora forest in the Loky-Manambato region in North-East Madagascar. Only 10-20 individuals were observed in the area during the vegetation study of the region.

Flowering time. – January.

Habitat and ecology. – Angraecum darainense was observed close to the ground in evergreen rainforest on large granitic rocks between 520 and 570 m elevation. It grows in forests with canopies reaching 10 to 14 m, with emergent trees reaching 16 m, with two sparse shrub strata at 3 to 4.5 and at 7 to 8 m high, and a very sparse suffrutescent stratum less than 1 m high.The most frequent species recorded together with Angraecum darainense in vegetation surveys are, in decreasing abundance: Cynometra commersoniana (DC.) Baill., Treculiaafricana subsp. madagascarica (N. E. Br.) C. C. Berg , one unidentified species of Dypsis Mart., Ravenalamadagascariensis Adans. and Scleria boivinii Steud.

Etymology. – The specific epithet refers to Daraina, the main village located in the central part of the Loky-Manambato region, which is the only known region where the new species occurs.

Conservation status. – With only one subpopulation included in the Loky-Manambato protected area, Angraecum darainense is assigned a preliminary status of “Critically Endangered” (CR) following the IUCN Red List Categories and Criteria ( IUCN, 2001). This species was collected rather early during the floristic survey, and we expected that several subpopulations should be observed later, because its habitat, the evergreen rainforest, is the third most frequent forest type in this region. It turned out that no additional fertile material of this species was encountered.

Figures

Fig. 1. – ngraecum darainense P. J. Cribb & Nusb. A. Habit; B. Apex of stem, leaves and flower; C. Flower; D. Flower, side view; E. Dorsal sepal; F. Lateral sepal; G. Petal; H. Lip and column, front view; I-J. Anther cap, dorsal and ventral views; K. Pollinia. [L. Nusbaumer & P. Ranirison 1430] [Drawn by Juliet Beentje-Williamson from the type collection]

Fig. 2. – Flowering shoot of the type collection of ngraecum darainense P. J. Cribb & Nusb. [L. Nusbaumer & P. Ranirison 1430] [Photo: L. Nusbaumer]