Dendrobium violaceum Kraenzl., in Engl., Pflanzenr. IV. 50. II. B. 21 (1910) 108.
Type: Micholitz s.n. (Milne Bay, Mitu) (holo HBG).
Erect tufted epiphyte, 8-30(-40) cm high. Roots to 1.5 mm diameter, white (purplish pink when moist). Rhizome short. Pseudobulbs 1-5(-7) by 0.3-1.5 cm, fusiform to ovoid, usually constricted at the nodes, (2-)3(-5) leaves arising together from the apex of new stems. Leaves 5-30 by 0.075-0.8(-1.1) cm, erect to spreading, jointed at base, linear occasionally linear-lanceolate, apex obtuse to subacute, often mucronate; sheaths slightly persistent. Inflorescences arising from the upper nodes of defoliated stems, subsessile, 1-4-flowered; peduncle 2-5 mm long; bracts 8-24 mm long, ovate, apiculate to acuminate. Flowers 2.8-4.5 cm long, usually widely opening, lasting c.6 months. Median sepal 12-20 by 4-7 mm, oblong-ovate, acuminate. Lateral sepals 27-45 by 8-14 mm, triangular, acuminate; basal fused part cylindrical, 4-15 mm long; mentum total length 15-28 mm, tip bilobed occasionally obtuse. Petals 9-16 by 2.5-4.5 mm, obliquely lanceolate-elliptic, apiculate to acuminate. Lip 22-37 by 3-5 mm, subtrilobate, linear-oblanceolate, adnate to column foot at base, margins slightly incurved, cross-ridge absent, apical part free, apex not recurved, acuminate. Column c. 4 mm long; foot 15-28 mm long; anther c. 3 mm broad; pollinia c.1. 5 mm long. Ovary with 5(-6) main wings and up to 8 (usually 4) additional smaller wings or ribs, dorsal wings usually undulate; pedicel and ovary 19-35 mm long. Fruit to 25 by 6 mm, narrowly pyriform.
(after Reeve & Woods, 1989).
Colours: Sepals and petals pink to deep violet, occasionally with bluish tips, rarely all blue or white; lip dark purple with orange to scarlet-red apex; pollinia dark in colour.
Habitat: Epiphyte in juvenile secondary forest, margins of primary montane forest, etc., rarely terrestrial or lithophytic. Altitude 750 to 2000 m.
Flowering time in the wild: See under the subspecies.
Distribution: New Guinea.
Distribution in New Guinea: See under the subspecies.
Map: VIOLCMAP.JPG [Dendrobium violaceum Kraenzl., distribution map, redrawn from T.M. Reeve & P.J.B. Woods, Notes Roy. Bot. Gard. Edinburgh 46 (1989) 288, map 11.]
Notes: Dendrobium violaceum is related to Dendrobium hellwigianum and Dendrobium pentapterum. It is a pretty species and apparently easier to grow than most of its 'Oxyglossum' relatives.
Cultivation: Intermediate growing epiphyte, prefers light position.
INFRASPECIFIC TAXA
Key to the subspecies:
1a. Leaves more than 2 mm broad ... Dendrobium violaceum Kraenzl. subsp. violaceum
1b. Leaves less than 2 mm broad ... Dendrobium violaceum Kraenzl. subsp. cyperifolium (Schltr.) T.M.Reeve & P.Woods.
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Dendrobium violaceum Kraenzl. in Engl., Pflanzenr. IV. 50. II. B. 21 (1910) 108, subsp. violaceum.
This subspecies is recognised by its wider leaves which are 2-11 mm broad.
Colours: Sepals and petals pink to deep violet, occasionally with bluish tips, rarely all blue or white; lip dark purple with orange to scarlet-red apex; pollinia dark in colour.
Habitat: Epiphyte in open montane forest. Altitude 750 to 2000 m.
Flowering time in the wild: Throughout the year.
Distribution: New Guinea.
Distribution in New Guinea: Papua (Central Mountain range) and Papua New Guinea, widespread.
Notes: Plants vary considerably in size and shape but the leaves are usually distinctive being long, linear and arising together from the top of the pseudobulbs. In exposed habitats plants have shorter, wider and more rigid leaves.
The ovary wings on the flowers are interesting as the number varies from 5 to as many as 13. However, there are always 5 or 6 main wings and the dorsal 3 are usually undulate, sometimes quite markedly. This degree of undulation has been found to increase if plants are exposed to greater sunlight.
A natural hybrid between Dendrobium violaceum and Dendrobium hellwigianum is recorded.
Cultivation: Growing as they do in fairly exposed habitats plants should be given plenty of light and air movement, while avoiding desiccation.
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Dendrobium violaceum Kraenzl. subsp. cyperifolium (Schltr.) T.M.Reeve & P.Woods, Notes Roy. Bot. Gard. Edinburgh (1989, publ. 1990) 236.
Basionym: Dendrobium cyperifolium Schltr.
Subsp. cyperifolium is distinguished from the typical subspecies by its narrow leaves 0.75-2 mm broad.
Colours: Sepals and petals pink to violet; lip dark purple with orange apex.
Habitat: Epiphyte in montane forest. Altitude 1200 to 1850 m.
Flowering time in the wild: January-May, August, September.
Distribution: New Guinea.
Distribution in New Guinea: Papua (Mt. Carstenz, Wissel Lakes, Idenburg River, Cyclops Mountains); Papua New Guinea (Sandaun, East Sepik and Enga Provinces).
Notes: Subsp. cyperifolium occurs mainly in West New Guinea but it is also recorded from the Lumi, Ambunti and Maramuni Districts on the Sepik River catchment in Papua New Guinea.
This subspecies represents a race found in the northern and western parts of the island.
(after Reeve & Woods, 1989)