Dendrobium (section Calyptrochilus Schltr.) centrosepalum Schuit., Juswara & Droissart, 2016

Juswara, Lina, Schuiteman, Andre & Droissart, Vincent, 2016, Four new orchid species from the Lengguru fold belt, West Papua, Indonesia, PhytoKeys 61, pp. 47-59 : 49-51

Dendrobium (section Calyptrochilus Schltr.) centrosepalum Schuit., Juswara & Droissart sp. nov. Figs 2B , 3E-H

Diagnosis.

The short and dense inflorescences with small, purple flowers and green-tipped, long-apiculate sepals resemble those of Dendrobium purpureum Roxb., a lowland species from Maluku and Sulawesi. However, the plant habit of the latter is completely different, as Dendrobium purpureum has robust, many-leaved, cane-like, tufted stems up to more than 50 cm long. Vegetatively, Dendrobium centrosepalum is more similar to Dendrobium aurantiroseum P.Royen ex T.M.Reeve from New Guinea, which also has unifoliate pseudobulbs on a creeping rhizome. However, the latter is a species from high elevations (2100-3350 m) with pink flowers that are about twice as large, while the sepals are not apiculate; in addition, the cross-ridge on the lip is situated below the middle in Dendrobium aurantiroseum and above the middle in Dendrobium centrosepalum .

Type.

Indonesia, West Papua Province, Kaimana Regency, Lobo village, Triton Bay, 03°43.7962'S, 134°3.5962'E, 28/10/2014, Droissart & Juswara 1736 (holotype: BO!, spirit material).

Description.

Epiphytic herb. Rhizome creeping, c. 3 cm long, growing downwards; roots 0.5 mm diam. Pseudobulbs closely spaced, erect, green tinged purplish, oblongoid-fusiform, 1.3-1.5 × 0.4 cm; main internodes 3; irregularly 5-ribbed; 1-leaved at apex, sometimes with a reduced additional leaf. Leaves glaucous green, deciduous, erect, narrowly elliptic, 3.3 × 1.1 cm; apex obtuse, minutely 3-dentate; margin smooth, slightly erose at apex; sheath very short. Inflorescence arising laterally from the upper internode of the leafless pseudobulb, erect, c. 12 mm long, c. 7-flowered; peduncle 5.2 mm long, covered by a few short scales in the basal part; rachis straight, 7 mm long. Floral bracts triangular, patent, 4.8 × 2.8 mm, apex acuminate, 3-nerved, glabrous. Pedicel-with-ovary narrowly clavate, c. 8.4 mm long, curved, with 5 rounded ribs, minutely papillose. Flower 10.5 mm long; sepals bright purple with greenish mucro; petals, lip and ovary bright purple. Sepals glabrous, but abaxially finely papillose on the slightly raised midvein; distinctly sharply apiculate at apex. Dorsal sepal ovate-oblong, 3.5 × 1.9 mm, 3-nerved; mucro 0.4 mm long. Lateral sepals obliquely narrowly ovate-oblong, much elongated in basal part, in total 10.8 × 2.8 mm, 4-nerved; mucro 0.9 mm long; mentum narrowly conical-cylindrical, 5.7 mm long, apex rounded, the closed apical part 4.8 mm long. Petals elliptic, 2.9 × 1.7 mm, emarginate, very shortly mucronate, 3-nerved, margin in upper half finely papillose. Lip when flattened subspathulate, 8.5 × 2.3 mm, at 5 mm above the base with a V-shaped transverse ridge, margins of the basal part adnate to the column-foot for 2.1 mm; apical part broadly elliptic, finely papillose along apical margin, apex rounded, minutely apiculate. Column rectangular, 1.9 mm long, wings truncate; foot 5.7 mm long; stigma semiorbicular, 0.8 mm wide, rostellum swollen, transversely oblongoid; anther cucullate-rectangular, 0.9 × 1.0 mm, minutely papillose, at base retuse, apex truncate and minutely erose; pollinia 0.7 mm long.

Distribution and habitat.

Dendrobium centrosepalum is only known from the Lengguru fold belt in West Papua. It is currently known from a single locality in the Triton Bay area, near the village of Lobo (Fig. 1 ). The only population seen so far was found in submontane forest at 1114 m elevation, the plants growing epiphytically on a thick, vertical, moss-and-lichen-covered trunk of a tree.

Etymology.

From the Greek centron, a sharp point, referring to the apiculate sepals.

Notes.

The small, bright purple flowers in short and dense inflorescences superficially resemble those of such species as Dendrobium dichaeoides Schltr. and Dendrobium limpidum Schuit. & de Vogel, but these are quite different vegetatively, having elongate, leafy stems; in addition, in these two species the sepals are not sharply apiculate. See the diagnosis for additional comparisons.

Figures

Figure 1. Main localities sampled during Lengguru 2014 expedition and distribution of the four new species in West Papua, Indonesia.

Figure 2. A Bulbophyllum leucoglossum: 1 flower 2 dorsal sepal 3 lateral sepal 4 petal; 5, lip, adaxial view 6 lip, abaxial view 7 detail of crest on lip 8 column and base of lip; all after Droissart & Juswara 1789; B Dendrobium centrosepalum: 1 flower 2 flower, lateral view 3 floral bract 4 dorsal sepal 5 lateral sepal 6 petal 7 lip 8 flower, cut open 9 column 10 anther 11 pollinia; all after Droissart & Juswara 1736; C Dendrobium taeniocaule: 1 flower 2 dorsal sepal 3 lateral sepal 4 petal 5 lip 6 mentum 7 column, lateral view 8 column, ventral view; all after Droissart & Juswara 1739; D Taeniophyllum pyriforme: 1 flower 2 dorsal sepal 3 lateral sepal 4 petal 5 lip 6 column 7 anther, dorsal view 8 anther, lateral view; all after Droissart & Juswara 1735. Single scale bar = 1 mm; double scale bar = 1 cm. Drawing: Judi Stone.

Figure 3. Photographs of living type specimens and habitats. Bulbophyllum leucoglossum: A habitat and habit B flower, side view C flower, front view D Flower close-up, showing details of the column and the labellum. Dendrobium centrosepalum: E habitat and habit F, G plant and inflorescence H inflorescence and flowers close-up. Photos: Vincent Droissart.