Species Information - Dendrobium sulphureum

Dendrobium sulphureum Schltr., Repert. Spec. Nov. Regni Veg. Beih. 1 (1912) 534; 21 (1923) t. 181, fig. 677.

Type: Papua New Guinea, Sandaun ProvinceEast 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).

Synonyms:

• Pedilonum sulphureum (Schltr.) Rauschert, Feddes Repert. 94 (1983) 464 (= var. sulphureum ).
• Dendrobium cellulosum J.J.Sm., Nova Guinea 14 (1929) 428, pl. 67, 77 (= var. cellulosum ).
  - Type: West New Guinea, Mt. Doorman, 2200m, 31 X 1920, Lam 1832 (BO, in alcohol).

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).

(largely after Reeve & Woods, 1989).

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.

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.

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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.

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.

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.

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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.

(largely after Reeve & Woods, 1989)

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