Orchids of New Guinea

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Dendrobium petiolatum

Dendrobium petiolatum Schltr., Repert. Spec. Nov. Regni Veg. Beih. 1 (1912) 541; 21 (1923) t. 183, fig. 686.

Type: Schlechter 18710 (holo B, lost; iso AMES, E, G, L, NSW).

Synonyms:

Pedilonum petiolatum (Schltr.) Rauschert, Feddes Repert. 94 (1983) 462.
Dendrobium unifoliatum Schltr., Repert. Spec. Nov. Regni Veg. 17 (1921) 375.
- Type: Kempter s.n. (Angriffshafen, Kaiser Wilhelmsland) (holo B, lost).

Erect to suberect tufted epiphyte, to 25 cm high. Roots 0.5-l mm diameter. Rhizome short. Pseudobulbs 0.5-4.5 by 0.5-1.6 cm, obclavate to shortly sub-fusiform, usually constricted at nodes and surrounded by fibres from decayed sheaths, apex 1-leaved (occasionally 2-leaved on small cultivated plants). Leaves 3-16 by 1.0-3.5 cm, erect to spreading, distinctly petiolate, oblong-elliptic to sub-ovate, apex subacute, mucronate; sheaths petioliform, to 4.5 cm long. Inflorescences arising terminally or laterally from defoliated pseudobulbs, 4-20-flowered in dense racemes (occasionally 1-2-flowered racemes are observed on small cultivated plants); peduncle distinct, 0.5-4 cm long (usually elongated when plant is embedded deep in moss); bracts ovate, acuminate. Flowers 1.4-2.1 cm long, long-lasting. Median sepal 6-13 by 2-3. 5 m., oblong-lanceolate, carinate, acuminate. Lateral sepals 14-21 by 3-4 mm, carinate, strongly acuminate; basal fused part 2.5-4 mm long, cylindrical to subconical; mentum total length 6-l0 mm, tip obtuse to truncate or bilobed. Petals 4-9 by 1-2 mm, linear-lanceolate, acute to acuminate. Lip 11-16 by 2-2.5 mm, subtrilobate, linear, adnate to column foot at base, with central U- or V-shaped cross-ridge, apex narrowly triangular, acute. Column c. 2 mm long; foot 6-l0 mm long; anther c. 1.25 mm broad; pollinia c. 1 mm long. Ovary 5(-6)-winged, pedicel and ovary 9-17 mm long. Fruit not observed.
(after Reeve & Woods, 1989).

Dendrobium petiolatum is characterised by its dense racemes of up to 20 flowers, the large petiolate leaves, the persistent fibres (from decayed sheaths) around the pseudobulbs, the long peduncles, the carinate sepals and the cross-ridge on the lip.

(largely after Reeve & Woods, 1989)

Colours:

Flowers bright magenta purple with orange to yellow lip apex.

Habitat:

Epiphyte in montane forest. This species often grows in large clumps of epiphytic mosses in deep shade on steep ridges where there is direct exposure to air movement. This appears to be a very delicate moisture/humidity/drainage balance. Altitude 800 to 2

Distribution:

New Guinea, Bismarck Archipelago (New Britain), Solomon Islands.

Distribution New Guinea:

Papua New Guinea (Enga, Southern Highlands, Western Highlands, Madang, Morobe and Milne Bay Provinces; New Britain).

Map: Dendrobium petiolatum Schltr., distribution map, redrawn from T.M. Reeve & P.J.B. Woods, Notes Roy. Bot. Gard. Edinburgh 46 (1989) 288, map 12.

Cultivation:

Intermediate to cool growing epiphyte, prefers shaded and humid but well drained position.

Flowering time in the wild:

May, November. Flowers last several months.

Literature:

Reeve, T.M. & P.J.B. Woods. 1990. Notes Roy. Bot. Edinburgh 46: 259, fig. 31, pl. 16C.
Lewis, B. & P.J. Cribb. 1991. Orchids of the Solomon Islands and Bougainville: 188.

Notes:

Dendrobium petiolatum has a reasonably wide distribution in East New Guinea, and is one of three Oxyglossum species so far recorded from New Britain. However, it is not common although it sometimes occurs abundantly in very restricted localities.