Dendrobium sulphureum Schltr., Repert. Spec. Nov. Regni Veg. Beih. 1 (1912) 534; 21 (1923) t. 181, fig. 677.
Type: Papua New Guinea, Sandaun Province: Torricelli Mountains., c. 800 m, ix 1909, Schlechter 20076 (B, lost). Neotype (designated by Reeve & Woods): Papua New Guinea, Enga Province, Lagaip district, Lake Inim, 2600m, Reeve 483 (neo E; isoneo AMES, CBG, K, L, LAE, UPNG).
Tufted epiphyte, 2-13 cm high, erect to semi-pendulous, often forming quite broad clumps or mats to 15 cm or more wide. Roots 0.5-0.8 mm diameter. Rhizome short. Pseudobulbs 0.3-10 by 0.1-0.5 cm, few to c.7-noded, ovoid to narrowly cylindrical 1-8-leaved mostly from nodes at upper half or terminal. Leaves 0.4-5(-6) by 0.1-0.55 cm, narrowly elliptic, oblanceolate or linear, texture either soft and then leaf often curved, or rigid and leaf usually straight, green sometimes purplish, apex obtuse or acute, narrowing towards base; sheaths often papery, persistent and only with age becoming fibrous. Inflorescences terminal or axillary, from leafy or leafless stems, 1-2(-4)-flowered; bracts 2-3 mm, ovate, apiculate to acuminate. Flowers 1.4-2.95 cm long, widely spreading, sepals and petals sometimes reflexed. Median sepal 4-11 by 1.5-4.5 mm oblong to ovate, apex obtuse to acute, sometimes apiculate. Lateral sepals 10-23 by 2-6 mm, obliquely oblong to triangular, apex obtuse to acute sometimes apiculate; basal fused part 2.5-7 mm, cylindrical; mentum total length 9-17.5 mm, tip blunt, often bilobed. Petals 3.5-11 by 1-2.5 mm, quite variable in shape, oblong to linear, sometimes spathulate, apex obtuse to acute or apiculate. Lip 12-23 by 2-3 mm, subtrilobate, narrowly oblong, adnate to column foot at base, upper margins slightly incurved, with an indistinct transverse V-shaped ridge, apex triangular-ligulate to acuminate, normally recurved. Column c. 2.6 mm long; foot 9-16 mm long; anther c. 1.8 mm wide; pollinia c. 1 mm long. Ovary triangular or rarely 5-ribbed; pedicel and ovary 10-23 mm long. Fruit to 13 by 8-9 mm, oblong-ovoid or globose, angular or trigonous, sometimes distinctly winged towards the pedicel, pendulous or sometimes erect.
(after Reeve & Woods, 1989).
Colours: Flowers bright yellow or greenish yellow, occasionally cream-white, lip green to blackish green, rarely yellow, apex bright orange-scarlet, anther green.
Habitat: Epiphyte on trunks and twigs in montane cloud forest, on forest edges of subalpine grassland and on trees in open grassland, in moss and rainforest. Recorded on tree ferns, Dacrycarpus compactus and Cordyline (also observed planted on Cordyline in village). Altitude (800-) 1800 to 3656m.
Flowering time in the wild: See under the varieties.
Distribution: New Guinea.
Distribution in New Guinea: See under the varieties.
Map: SULPHMAP.JPG [Dendrobium sulphureum Schltr., distribution map, redrawn from T.M. Reeve & P.J.B. Woods, Notes Roy. Bot. Gard. Edinburgh 46 (1989) 285, map 5.]
Notes: Like many orchids collected and named by Schlechter, Dendrobium sulphureum was described from a specimen which was lost in the destruction of the Berlin herbarium on the night of 1-2 March, 1943. This single collection, of which no duplicates have been found, was collected during September 1909 in the Torricelli Mountains. in north-west Papua New Guinea. Eleven years later, on 31 October 1920, H. J. Lam collected a plant at 2200m on Doorman Top which is on the northern side of the main mountain chain in the western half of the island some 340 km to the west of Schlechter's locality. T.M.Reeve & P.Woods (1989) have not been able to examine this specimen which was preserved in alcohol and on which J. J. Smith based his description of Dendrobium cellulosum. They therefore only had Schlechter's and Smith's descriptions, each of which is fortunately supplemented by a dissectional drawing of a flower, on which to establish their identifications of the 60 or more available collections, all but one of which are from East New Guinea. The differences between the three varieties recognised by Reeve & Woods are not clear cut, rather they have attempted to formalise what appears to be a 3-modal variability in the specimens they have examined.
(largely after Reeve & Woods, 1989).
Cultivation: Cool growing epiphyte, prefers light position.
INFRASPECIFIC TAXA
Key to the varieties:
1a. Pseudobulbs mostly stem-like, cylindrical, elongated, often branched below, 4- or more noded (if short, flowers usually not more than 2 cm long by 1.5 cm wide); leaves 2-5(-8) scattered along upper part of stem, or apical, 6 or more times longer than broad ... 2
1b. Pseudobulbs ovoid or conical, usually less than 4-noded; leaves usually 2, apical, less than 6 times longer than broad; flowers usually 2 cm or more long by 1.7-2.5 cm wide ... Dendrobium sulphureum Schltr. var. cellulosum (J.J.Sm.) T.M.Reeve & P.Woods.
2a. Leaves rigid, erect, often in one plane and distichous; flowers usually more than 2 cm long by 1.5 cm wide, sepals and petals distinctly upward curved (i.e. upper surface concave) ... Dendrobium sulphureum Schltr. var. rigidifolium T.M.Reeve & P.Woods
2b. Leaves firm but not stiffly rigid, spreading, margin often slightly undulate, not distichous; flowers usually less than 2 cm long by 1.5 cm wide ... Dendrobium sulphureum Schltr. var. sulphureum.
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Dendrobium sulphureum Schltr., Repert. Spec. Nov. Regni Veg. Beih. 1 (1912) 534; 21 (1923) t. 181, fig. 677, var. sulphureum.
Var. sulphureum shares with var. rigidifolium the longer cylindrical stems but it has smaller flowers and spreading, less rigid leaves. Short-stemmed forms are very similar to var. cellulosum but may be recognised by their normally much smaller flowers.
Colours: Flowers bright yellow or greenish yellow, occasionally cream-white, lip green to blackish green, rarely yellow, apex bright orange-scarlet, anther green.
Habitat: On rainforest and moss forest trees, often on Cordyline, on moss covered branches, usually in somewhat exposed positions, also in roadside forest and bamboo regrowth. Altitude (800-) 1800 to 2700 (-3450) m.
Flowering time in the wild: February, April, June, August.
Distribution: New Guinea.
Distribution in New Guinea: Papua (Cyclops Mountains); Papua New Guinea (Sandaun, Enga, Southern Highlands, Western Highlands, Chimbu, Eastern Highlands, Madang, Morobe and Central provinces).
Notes: Schlechter's description is based on only one collection of what Reeve & Woods (1990) interpret to have been a small and probably atypical plant, in which the ellipsoid-obclavate stems and leaves, 0.7-1.3 by 0.25-0.4 cm, are much smaller than what they believe to be the average.
The low altitude of 800 m at which Schlechter originally collected the type obviously represents a cool climatic pocket, as this taxon is normally found above 1800 m.
Cultivation: Cool growing epiphyte, requires light shade and excellent drainage.
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Dendrobium sulphureum Schltr. var. rigidifolium T.M.Reeve & P.Woods, Notes Roy. Bot. Gard. Edinburgh (1989, publ. 1990) 200, fig. 9, pl. 6A.
Type: East New Guinea. Eastern Highlands District, Mt. Wilhelm, Kombugomambuno, base of Pindunde (Pindaunde) grass valley, 3300m, 3 v 1965, Balgooy 190 (holo L; iso CANB, LAE).
Var. rigidifolium differs from the type variety in its erectly held, rigid, distichous leaves and larger flowers with recurved sepals and petals and, in addition from var. cellulosum, in its longer stems the sheaths of which often appear to remain membranous. The lateral sepals in addition to being upward curved are also often concave along their upper surfaces.
Colours: Flowers bright yellow or greenish yellow, occasionally cream-white, lip green to blackish green, rarely yellow, apex bright orange-scarlet, anther green.
Habitat: Epiphyte in subalpine grassland and forest on Dacrycarpus and tree ferns, montane moss forest or rarely in rain forest. Altitude 1920 to 3650 m.
Flowering time in the wild: May to December.
Distribution: New Guinea.
Distribution in New Guinea: Papua New Guinea (Enga, Western Highlands, Chimbu, Eastern Highlands, Madang, Morobe, Central and Milne Bay Provinces).
Notes: Plants of distinctive dwarf habit have been observed e.g. Reeve 1042 from Tomba, 2800m, in Western Highlands Province; Reeve 272, Mt. Alupai, 2900m, Enga Province and Woods with Cruttwell et al. 2490, Mt. Simpson area between 2000 and 2376m, Milne Bay Province.
Most of the collections examined by Reeve & Woods have been found at fairly high altitudes (2740 to 3650 m). Dendrobium sulphureum reaches its most southerly and easterly limits with the records of var. rigidifolium from Central and Milne Bay Provinces.
Cultivation: As for var. sulphureum, but apparently (even) more difficult to grow.
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Dendrobium sulphureum Schltr. var. cellulosum (J.J.Sm.) T.M.Reeve & P.Woods, Notes Roy. Bot. Gard. Edinburgh (1989, publ. 1990) 202.
Basionym: Dendrobium cellulosum J.J.Sm.
Var. cellulosum differs from var. rigidifolium in the shorter stems and fewer, broader, elliptic leaves. It has larger flowers than in var. sulphureum. The flowers often seem to overtop the leaves.
Colours: Flowers bright yellow or greenish yellow, occasionally cream-white, lip green to blackish green, rarely yellow, apex bright orange-scarlet, anther green.
Habitat: Epiphyte on trees in montane forest, tree ferns on forest edges and alpine grassland. Altitude 2200 to 3450 m.
Flowering time in the wild: January, February, July, August.
Distribution: New Guinea.
Distribution in New Guinea: Papua (Mt. Doorman, ? Cyclops Mountains); Papua New Guinea (Enga, Southern Highlands, Chimbu and Eastern Highlands provinces).
Notes: The flowers of var. cellulosum are large in comparison to its overall height and the size of the leaves. This makes it a most attractive plant but despite this it does not seem to have been successfully introduced into cultivation.
Cultivation: Probably as for var. rigidifolium.
(largely after Reeve & Woods, 1989)