Orchids of New Guinea

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Dendrobium rhodostictum

Dendrobium rhodostictum F.Muell. & Kraenzl., Österr. Bot. Zeitschr. 44 (1894) 300.

Type: Sayer s.n. (1887, Bourawarri (camp 9), New Guinea) (holo HBG).

Synonyms:

Sayeria rhodosticta (F.Muell. & Kraenzl.) Rauschert, Feddes Repert. 94 (1983) 468.
Dendrobium madonnae Rolfe ex Hook.f., Bot. Mag. 129 (1903) t. 7900.
- Type: Sander cult. s.n. (1899, New Guinea) (holo K).

Epiphytes or sometimes terrestrials, herbaceous, erect. Pseudobulbs tufted, narrowly fusiform (New Britain), or thin reedlike with only the 3-5-upper internodes abrubtly and markedly dilated into an ovoid pseudobulb (Bougainville), 9-25 by 0.3-1.2 cm, 2-4-leaved at apex. Leaves suberect or spreading, coriaceous, ovate-lanceolate to linear-lanceolate, minutely emarginate at acute to obtuse apex, 5-11 by 1-2.5 cm. Inflorescences apical or subapical, erect to arcuate, few-flowered; bracts elliptic, acute, 3-4 mm long. Flowers subnutant, white with purple spots on side margins of lip; pedicel and ovary 2.5-3.5 cm. Dorsal sepal ovate, acute or acuminate, 1.8-2.5 by 1 cm; lateral sepals falcate-lanceolate, acuminate, 1.8-2.2 by 1-1.1 cm; mentum obliquely conical, 8-10 mm long. Petals obovate-spathulate, obtuse to apiculate, 3-3.5 by 1.5-2.4 cm. Lip obscurely 3-lobed towards apex, broadly obovate in outline 1.9-2.6 by 1.8-2.8 cm; side-lobes erect-incurved, semicircular, often overlapping and larger than midlobe ; midlobe often obscure, transversely oblong to ovate, apiculate; callus 3-ridged above, raised and 3-lobed at base. Column 2.5 mm long; foot 7-9 mm long.
(after Cribb, 1983).

Colours:

Paeudobulbs dull yellowish. Flowers white with purple spots on side margins of lip.

Habitat:

Epiphyte in montane forest on Castanopsis, Nothofagus, etc. or terrestrial on steep wet mossy slopes; 800-1200 m.

Distribution:

New Guinea, Bismarck Archipelago, Solomon Islands.

Distribution New Guinea:

Papua New Guinea (Karkar Island; Milne Bay Province; New Britain; New Ireland).

Map: Dendrobium rhodostictum F.Muell. & Kraenzl., distribution map, redrawn from P. Cribb, Kew Bull. 38 (1983) 250, map 4.

Cultivation:

Intermediate growing epiphyte.

Flowering time in the wild:

January, May, June.

Classification:

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

Literature:

Cribb, P.J. 1983. Kew Bull. 38: 268, fig. 8E, F, 10, pl. 13A, B, map 4.
Lewis, B. & P.J. Cribb. 1991. Orchids of the Solomon Islands and Bougainville: 179, pl 10B.
Schlechter, R. 1912. Repert. Spec. Nov. Regni Veg. Beih. 1: 491.
Schlechter, R. 1923. Repert. Spec. Nov. Regni Veg. Beih. 21: t. 167, fig. 621.

Notes:

Characteristic for Dendrobium rhodostictum F.Muell. & Kraenzl. is the broad lip, which is three-lobed, apiculate, difficult to flatten and has rose-purple spots outside on the lateral margins and similar coloured stripes on the inside of the lip, which both shimmer through on the other side.

Specimens from New Britain have somewhat larger flowers with a more markedly three-lobed lip than those from New Guinea or Bougainville, and in addition also have pseudobulbs which are somewhat swollen along their entire length, instead of abruptly dilated in the apical part. Contrary to Cribb's (1983) opinion, we think that the vegetative and floral differences may warrant taxonomic recognition at subspecies level.