Orchids of New Guinea

Dendrobium rumphiae

Dendrobium rumphiae Rchb.f., in Walp., Ann. Bot. Syst. 6 (1861) 303

Type: Zippel 16 (L, probably holotype, labelled by Blume).

Synonyms:

Cadetia angustifolia Blume, Rumphia 4 (1849) 39
Cadetia bigibba Schltr., Repert. Spec. Nov. Regni Veg. Beih. 1 (1912) 432; 21 (1923) t. 149, fig. 560.
- Type: Schlechter 19204 (holo B, lost; iso AMES, BO, E, G, K, L, NSW, S).
Dendrobium alexisense J.J.Sm., Bull. Jard. Bot. Buitenzorg, sér. 2, 8 (1912) 18.
Cadetia crenulata Schltr., Repert. Spec. Nov. Regni Veg. Beih. 1 (1912) 430; 21 (1923) t. 149, fig. 557.
- Type: Schlechter 17427 (holo B, lost); para: Schlechter 19318 (B, lost; E, K, L).
Dendrobium dubium J.J.Sm., Bull. Jard. Bot. Buitenzorg, sér. 2, 8 (1912) 17.

Rhizome very short. Stems crowded, slender, subclavate, sharply 4-winged, 3.5-7 cm long, c. 3 mm diameter. Leaf falcate, linear, 3.5-7 cm by 5-9 mm, base rounded, apex obtuse, minutely unequally bilobulate. Inflorescences terminal from the leaf axil, solitary; spathe c. 1 cm long, 2 mm wide. Peduncle 5.7 mm long. Pedicel 0.5 cm long, ovary 3-winged, with 3 lower ribs alternating with the wings, o.4 cm long. Flower c. 1 cm long. Dorsal sepal ovate, 5.3 cm by 2.8 mm, apiculate. Lateral sepals obliquely ovate-triangular, 0.6 by 3.3 mm, apiculate; mentum elongated, parallel with the ovary, spur-like, 0.45 cm long, near apex in front side abruptly inflated. Petals reflexed, obliquely lanceolate, 0.5 cm long, in the middle c. 1 mm wide, at the base dilated, 1.5 mm wide. Lip 3-lobed, narrowly clawed, 0.67 by 0.45 cm (excluding the claw), disc pubescent in the centre; lateral lobes erect, obliquely quadrangular, front margins crenulate; midlobe porrect, oblong-obovate, 0.4 by 0.26 cm, fleshy, with 3 thick keels which are papillose in the middle part, apex obtuse. Column 2.3 cm long, stelidia triangular, longer than the filament; column-foot pubescent at the base.
(habit described only after the type collection, floral details after Smith, 1909).

Colours:

Sepals and petals white, lip white, midlobe orange-yellow in the centre.

Habitat:

Epiphyte in swamp forest, lowland rainforest and hill forest. Altitude 0-600 m.

Distribution:

New Guinea (endemic).

Distribution New Guinea:

Papua (Yapen-Waropen and Merauke Regencies); Papua New Guinea (Madang, Morobe, and Oro Provinces).

Map: Dendrobium rumphiae Rchb.f., distribution map.

Cultivation:

Warm growing epiphyte.

Flowering time in the wild:

February-July. Flowers last 10-14 days (fide O'Byrne).

Literature:

Smith, J.J. 1909. Nova Guinea 8, 1: 52, t. 19, fig. 59.
Smith, J.J. 1916. Nova Guinea 12, 3: 282.
O'Byrne, P. 1994. Lowland Orchids of Papua New Guinea: 162, fig., pl. (as Cadetia quinquecostata auct. non J.J.Sm.: O'Byrne).

Notes:

Dendrobium rumphiae is closely related to Dendrobium versteegii and Dendrobium stenocentrum. It differs in the narrower, not emarginate midlobe, the crenulate margins of the lateral lobes, and in the colour of the lip, which is marked with yellow, not rose-purple as in the other species. The leaves can be somewhat broader than as described here, up to c. 1.7 cm wide.