Dendrobium rupestre

Dendrobium rupestre J.J.Sm., Bull. Jard. Bot. Buitenzorg, sér. 2, 2 (1911) 15; Nova Guinea 12, 1 (1913) 64, t. 17, fig. 52.

Type: Kock, de 166 (lecto BO); para II (BO).

Small creeping, occasionally tufted, epiphytic, lithophytic or terrestrial plant, to 6 cm high, sometimes forming large mats. Roots to 1.5 mm diameter, tips usually orange. Rhizome prostrate, branched, to 1.7 cm long. Pseudobulbs 0.5-2.5 by 0.3-0.7 cm, very variable in shape from shortly globose or ovoid to cylindrical, apex 1-2-leaved. Leaves 0.7-4.5 by 0.3-1.4 cm, elliptic to lanceolate, apex acute-mucronate, minutely pitted on top, green, usually purplish underneath; sheaths smooth or slightly ribbed, persistent. Inflorescences terminal, 1-3-flowered, subsessile; bracts ovate, acute to apiculate. Flowers 1.8-3.3 cm long, usually widely opening up to 3.2 cm broad, long lasting. Median sepal 8.5-15 by 3-5.5 mm, ovate-elliptic to ovate-oblong, acute mucronate to subacuminate. Lateral sepals 17-30 by 4-7. 5 mm., obliquely ovate-oblong, acute to subacuminate, keeled; basal fused part 3-6 mm long, subconical; mentum total length 9-16 mm long, tip obtuse or bilobed. Petals 8-14 by 2.5-4.5 mm, lanceolate-spathulate, acute to apiculate. Lip 16-25 by 3-4 mm, subtrilobate, oblanceolate, adnate to column foot at base, apical margins incurved, apex narrowly-triangular to acuminate, not recurved. Column c. 3 mm long; foot 9-16 mm long; anther c. 2.5 mm broad; pollinia c. 1.5 mm long. Ovary distinctly 3-winged; pedicel and ovary 14-28 mm long. Fruit 18 by 9.5 mm, ovoid.
(after Reeve & Woods, 1989).

Colours: Root tips usually orange. Flowers bright purple with lip apex orange (rarely flowers pale purple or greenish yellow).

Habitat: Epiphyte in montane forests, particularly on Nothofagus, occasionally terrestrial or lithophytic in exposed. Altitude 1500 to 3100 m.

Flowering time in the wild: January, February, April, September, November.

Distribution: New Guinea.

Distribution in New Guinea: Papua (Treub Mountains; south of Mt. Trikora and Mt. Goliath); Papua New Guinea (Western, Southern Highlands, Enga, Western Highlands, Simbu, Morobe, and Oro Provinces).

Map: RUPESMAP.JPG [Dendrobium rupestre J.J.Sm., distribution map, redrawn from T.M. Reeve & P.J.B. Woods, Notes Roy. Bot. Gard. Edinburgh 46 (1989) 287, map 10.]

Notes: Although not a common species, Dendrobium rupestre does have a fairly wide distribution in New Guinea. Usually it is seen as an epiphyte in Nothofagus forests where it may form large mats, but in suitably exposed habitats it may grow terrestrially or as a lithophyte in association with mosses.

The first recording of Dendrobium rupestre was from West New Guinea, on Mt. Goliath at 2800 m, and the correct altitude was published with the original description. However the subsequent lengthier description given by J. J. Smith (1913) stated the altitude incorrectly as 3800 m. This error, which was probably typographic, has been copied by subsequent authors, but it is clearly an impossibility as the summit of Mt. Goliath is only 3340 m! Dendrobium rupestre does however grow at up to 3100 m so was properly included as an alpine species by van Royen (1979). His illustration of Sayers NGF 21211 in fig. 143 is correct, but the description is based on more than one species including different varieties of Dendrobium vexillarius (Kloss s.n., Kalkman 5186, Brass 9434).

Cultivation: This attractive species has proved to be very difficult to cultivate and prefers to grow amongst live mosses in what appears to be a very delicate moisture-humidity drainage balance.
(after Reeve & Woods, 1989)