Orchids of New Guinea

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Dendrobium cleistanthum

Dendrobium cleistanthum de Vogel, E.Winkel & Vugt, Malesian Orchid J. 18 (2016) 105.

Type: Leiden cult. 20032496 (E.F. de Vogel et al.) (holo LAE; iso L).

Epiphyte, (sub)erect. Roots 0-7 per internode, glabrous, not branched, terete, up to 0.1 cm wide. Rhizomes tufted, several short, some elongated, sub-erect to patent, stem-like, sparsely branching, filiform, flexuous, to 32 cm long, glabrous; internodes terete, somewhat flattened, widening to the top, 1-2 by 0.2-0.4 cm, covered by the long persistent, dried, membranous scale leaf from the node below it which reaches to almost its top. Pseudobulbs 1-leaved, narrowly ellipsoid, distinctly laterally flattened, 1.6-4 by 0,8-1.3 by c. 0.7 cm, covered by the long persistent, dried, membranous scale leaf from the node below it which reaches to almost its top. Leaves thin, rather stiff, sessile ovate-oblong, 4.5–9.5 by 1.7-3.5 cm, index 2.5-3; base broadly rounded; apex acute. Inflorescences in fascicles from the top of the pseudobulb, usually on the abaxial side of the leaf, very short, 1-flowered; the base covered by few dry scale leaves c. 0.7-0.9 mm long; peduncle c. 0.5 cm long. Pedicel and ovary c. 0.7 cm long, slender, shallowly 6-grooved; ovary with scattered flakey scales. Flowers not opening, c. 0.3 cm across. Sepals broadly sessile, with scattered scale hairs which are rather dense at their top. Median sepal triangular, concave, c. 0.4 by 0.45 cm; apex acuminate with rounded tip. Lateral sepals triangular, slightly oblique, concave, c. 0.4 by 0.4 cm; apex acute; mentum absent. Petals rather broadly attached, c. elliptic, c. 0.35 by 0.18 cm; apex shortly acuminate. Lip rather broadly attached, c. rhombic with rounded lateral corners to almost circular, c. 0.38 by 0.3 cm; without ornamentation; apex shortly acuminate. Column in lateral view c. 0.15 by 0.15 cm, c. 0.25 cm wide; clinandrium in front with a large triangular tooth, laterally with 4 broadly rounded lateral lobules (of which the two front ones sometimes developed in a large triangular tooth, at the back with a small narrow filament; stigma and column-foot not developed. Anther cucullate, in outline trapeziform to reniform, c. 0.12 by 0.18 cm; apex broadly rounded; pollinia banana-shaped, convex above, flat below.
(after De Vogel, Winkel & Van Vugt 2016)

Colours:

Roots white. Rhizome; internodes where exposed moss green; dried scale leaves whitish. Dried pseudobulb scale leaves whitish. Leaf blade mid-green, below lighter so. Flowers light green.

Habitat:

Primary forest c. 20-25 m high, , also when very disturbed, with little undergrowth, either or not along stream. Altitude 1500-1800 m.

Distribution:

Malesia (New Guinea, endemic).

Distribution New Guinea:

Papua New Guinea (Western Highland Prov.).

Cultivation:

Cool growing epiphyte, tolerates exposure, easy in cultivation. At the Hortus botanicus Leiden it is grown in a greenhouse where temperatures in the summer period are attempted to be kept during the day at 20 degrees Celsius and by ventilation during the

Flowering time in the wild:

June; in cultivation in Hortus Leiden in October.

Classification:

Family Orchidaceae
Subfamily Epidendroideae
Tribe Dendrobieae
Subtribe Dendrobiinae
Genus Dendrobium
Section Crinifera
Species Dendrobium cleistanthum

Notes:

Dendrobium cleistanthum de Vogel, E.Winkel & Vugt resembles Dendrobium homoglossum Schltr., also a cleistogamous species occurring in PNG, but differs in the smaller, entirely closed flowers (versus somewhat opening), the large triangular tooth blocking the front opening of the clinandrium (versus tooth absent), the rhombic lip with acute tip (versus oblong-rectangular with truncate top and the apiculate tip from below the top), as well as in the shorter and broader sepals and petals.