Orchids of New Guinea

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Dendrobium polysema

Dendrobium polysema Schltr., in K.Schum. & Lauterb., Nachtr. Fl. Deutsch. Schutzgeb. Südsee (1905) 163; Repert. Spec. Nov. Regni Veg. Beih. 21 (1923) t. 167, fig. 628.

Type: Schlechter 14046 (holo B, lost).

Synonyms:

Sayeria polysema (Schltr.) Rauschert, Feddes Repert. 94 (1983) 468.
Dendrobium polysema Schltr. var. pallidum Chadim, Austral. Orchid Rev. 29 (1964) 32.
- Type: Chadim D7 (holo K).
Dendrobium macrophyllum A.Rich. var. stenopterum Rchb.f., Gard. Chron. (1888, I) 393.
- Type: Bull cult. s.n. (holo W).
Dendrobium pulchrum Schltr., Repert. Spec. Nov. Regni Veg. Beih. 1 (1912) 496; 21 (1923) t. 169, fig. 629.
- Type: Schlechter 19605 (holo B, lost).
Dendrobium stenopterum (Rchb.f.) Chadim, Orchadian 4: 28(1972).

An epiphytic herb. Pseudobulbs clavate, 20-50 by 1.5-3 cm, drying yellow or orange, 3-5-noded below leaves, 2-leaved at apex. Leaves spreading, coriaceous, elliptic or oblong-elliptic, obtuse, up to 22 by 6-13 cm, shortly petiolate. Inflorescences terminal, erect to arcuate, few- to many-flowered, up to 45 cm long; peduncle terete, with 3 well-spaced sheaths along length; bracts lanceolate, acute, 1.5-2.5 by 0.6 cm. Flowers medium-sized to large, setose on outer surface; pedicel and ovary 3.6-5 cm long, densely setose. Dorsal sepal ovate-lanceolate, acuminate, 2-2.4 by 1.2-1.4 cm; lateral sepals obliquely falcate-lanceolate, acuminate, 2.3-3 by 1.5 cm; mentum incurved-conical, 1.2 cm long. Petals often reflexed, oblanceolate or obovate, apiculate, 1.8-2.6 by 0.7-1.6 cm, with ± strongly undulate margins. Lip 3-lobed, recurved, 1.8-2.3 by 2-2.6 cm when flattened; side-lobes smaller than midlobe , erect or incurved, tapering to a rounded apex; midlobe flat or with incurved margins, transversely oblong-ovate, subapiculate; callus 3-ridged, with a 4 mm long somewhat dilated free apex. Column short, 3-3.5 mm long, with an upcurved hook on each side at apex; foot incurved, 1.2 cm long.
(after Cribb, 1983).

Colours:

Sepals yellow or greenish, heavily spotted maroon; petals cream, spotted maroon; lip yellow, spotted maroon on midlobe and striped maroon on side-lobes; callus creamy white.

Habitat:

Epiphyte on tree trunks and thick branches in montane forest. Altitude 1200 to 1900 m.

Distribution:

New Guinea, Solomon Islands, Vanuatu.

Distribution New Guinea:

Papua New Guinea, widespread, but apparently not west of the Bismarck range.

Map: Dendrobium polysema Schltr., distribution map, redrawn from P. Cribb, Kew Bull. 38 (1983) 234, map 2.

Cultivation:

Intermediate growing epiphyte.

Flowering time in the wild:

January, May, June, August.

Classification:

Family Orchidaceae
Subfamily Epidendroideae
Tribe Dendrobieae
Subtribe Dendrobiinae
Genus Dendrobium
Section Latouria
Species Dendrobium polysema

Literature:

Clements, M. A. and Spence, P. 2017. Re-interpretation of the Dendrobium polysema Schltr. complex (Orchidaceae: Dendrobieae). Australian Journal of Botany 82(2): 2–23.
Cribb, P.J. 1980. Curtis's Bot. Mag., n.s. (1980) t. 798.
Cribb, P.J. 1983. Kew Bull. 38: 249, fig. 1A-C, pl. 11E.
Lewis, B. & P.J. Cribb. 1991. Orchids of the Solomon Islands and Bougainville: 178, fig. 41, pl. 10D.
Schlechter, R. 1912. Repert. Spec. Nov. Regni Veg. Beih. 1: 496.

Notes:

Dendrobium polysema Schltr. is closely allied to the widespread Dendrobium macrophyllum A.Rich. but is readily distinguished by its two-leaved pseudobulbs, broader elliptic leaves and the tapering side-lobes and the heavily spotted midlobe of its lip. Its flowers often open widely with the petals often reflexed and the midlobe deflexed giving the flower a flat appearance. Flower size is variable, the larger forms wer54e known as Dendrobium pulchrum.
(after Cribb, 1983).