Aeranthes unciformis 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 : 272-274

Aeranthes unciformis P. J. Cribb & Nusb. , spec. nova

( Fig. 3 & 4 ).

Typus: M ADAGASCAR: province de Diego-Suarez / Antsiranana, sous-préfecture de Vohemar, commune rurale de Daraina , forêt de Bekaraoka, partie nord , 13°06’S 49°42’E, 177 m, fl., 13.II.2004, L.Nusbaumer & P.Ranirison 1168 (holo-: G!; iso-: P, K!, MO!, TAN, herbarium of Daraina).

HabituA.laxiflorae similissed floribus majoribus et calcari longiorediffert; affinisA.caudatae sed plantaminore, foliisminoribus, inflorescentiisbrevissimis 25-30 mm longis 2-3-floris; pedunculobrevissimo 1-2cm longo, labello ad basinlateelliptico longe acuminatoet calcari elongate recto 22-24 mm longo bene distincto.

An epiphyte herb on trees with a very short stem; roots adventitious, slender, 1-1.5 mm in diameter. Leaves 4-5, distichous, twisted at the base to lie in one plane, oblanceolateoblong, obtusely obliquely bilobed at the tip mostly with a longer distal lobe and a shorter proximal lobe, 6-8 0.9-2 cm, articulated at the base to a short conduplicate leaf base. Inflorescences much shorter than the leaves, axillary, 1- to 3- flowered, 25-30 mm long; peduncle terete, 10-12 mm long; bracts small, ovate, acuminate, 4-4.5 mm long. Flower resupinate, large for the size of the plant, translucent, white; pedicle and ovary 20 mm long, scabrid. Dorsal sepal curving forwards over the column and lip, linear-tapering, longly caudate, 65-85 3 mm; lateral sepals spreading-decurved, falcate at base, linear-tapering, longly caudate, 55-60 4.5-5 mm. Petals spreading upwards, linear-tapering, caudate, 29-30 5-6 mm. Lip ecallose, somewhat porrect, concave, broadly ovate, caudate, ciliate along the margin of the tapering part, 38-50 20- 22 mm; spur with a broad mouth then narrowly cylindrical, straight, 22-24 mm long. Column 5 mm long, with two recurved lateral arms at the tip, each 2 mm long; anther cap broadly cordiform; viscidia 2, strap-like, 2 mm long.

Notes. – Aeranthes unciformis is very distinct in the genus. It has the habit of A. laxiflora Schltr. , a widespread species in the Mountains of Madagascar, but quite different and much larger flowers. Its flowers are somewhat reminiscent of those of A.caudata Rolfe but much larger with longer acumens and are borne two or three at a time in a short inflorescence, rather than appearing in succession on slender elongate wiry branching peduncles. The lip is very distinctive, almost transversely elliptic at the base then drawn out and tapering into a long acumen at the tip. The spur, 22-24 mm long, is also much longer than in most Aeranthes species. The dorsal sepal is very peculiar, curving forwards over the column and lip.

Distribution. – The species is only known from the type locality in the northern part of the Bekaraoka forest in the Loky-Manambato region in North-East Madagascar. About 20 individuals were observed in the area during the vegetation study.

Flowering time. – February.

Habitat and ecology. – Aeranthes unciformis was recorded in dry deciduous forest close to a seasonal river at 170 m elevation. This epiphytic plant occurs on trunks of trees at 2 to 4 m above ground. It grows in forests with canopies reaching 8 to 12 m, with emergent trees reaching 14 m, with an shrub stratum at 3 to 5 m high, and a sparse suffrutescent stratum less than 0.5 m high.

The most frequent species recorded together with Aeranthes unciformis are: Dracaena xiphophylla Baker , Euonymus pleurostylioides (Loes.) H. Perrier , Diospyros pruinosa Hiern and Acalypha aff. perrierii Leandri.

Etymology. – The specific epithet refers to the morphology of the dorsal sepal curving forwards over the column and lip.

Conservation status. – With only one subpopulation, included in the Loky-Manambato protected area, Aeranthes unciformis is assigned a preliminary status of “Critically Endangered” (CE) 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 other subpopulations should be observed later, because its habitat dry deciduous forest is the most frequent forest type in this region. It turned out that no further fertile material has been collected.

Figures

Fig. 3. – Aeranthes unciformis P. J. Cribb & Nusb. A. Habit; B. Dorsal sepal; C. Lateral sepal; D. Petal; E. Lip, ovary and column, oblique view; F. Column apex, oblique view; G. Anther, ventral view; cap, dorsal and ventral views; H. Pollinarium; I. Pollinium. [L. Nusbaumer & P. Ranirison 1168] [Drawn by Juliet Beentje-Williamson from the type collection]

Fig. 4. – Flowering type collection of Aeranthes unciformis P. J. Cribb & Nusb. [L. Nusbaumer & P. Ranirison 1168] [Photo: L. Nusbaumer]