Dendrobium rigidifolium

Dendrobium rigidifolium Rolfe, Bull. Misc. Inform. Kew (1899) 110.

Type: Giulianetti s.n. (Mt. Scratchley, 12200 ft) (holo K).

An epiphytic or terrestrial herb. Pseudobulbs clustered, cylindrical, 4-20-noded below leaves, 7-68 by 0.6-0.9 cm, often drying orange, 2-10-leaved in apical half or third. Leaves coriaceous, well-spaced, flat to conduplicate, linear to oblong to elliptic, rounded or obtuse, up to 4-10 by 1.3-5 cm, shortly petiolate. Inflorescences erect to erect-spreading, 11-32 cm long, 2-15-flowered; peduncle very short; bracts cucullate, oblong-triangular to elliptic, subacute to acuminate, 0.7-2 cm long. Pedicel and ovary 2.7-4.5 cm long. Dorsal sepal narrowly elliptic, obtuse (apiculate), 1.6-2.3 by 0.5-0.7 cm; lateral sepals obliquely falcate-lanceolate, acuminate, 2.0-2.7 by 0.8-1.1 cm; mentum bluntly conical, 6-10 mm long. Petals elliptic to oblong-obovate, acuminate to obtuse, 2-2.3 by 0.7-1 cm. Lip subentire to distinctly 3-lobed, somewhat rhombic or elliptic in outline, 1.5-1.9 by 0.7-1.3 cm; side-lobes semicircular, broadly rounded to almost truncate, apical margin more or less erose; midlobe ovate to triangular, acute to acuminate, longer than side-lobes; callus extending to the base of the midlobe, 3-ridged, rugulose towards apex. Column 2 mm long, with obtuse stelidia at apex; column foot straight or incurved, flushed purple, 6-10 mm long.
(largely after Cribb, 1983, but including Dendrobium rhomboglossum & Dendrobium acutisepalum, see Note below).

Colours: Flowers white to crimson, flushed purple on mentum and heavily marked with purple or brown on the yellowish lip.

Habitat: Epiphyte in montane forest on Nothofagus etc., or terrestrial in deep moss and in open, marshy vegetation. Altitude 1750 to 3800 m.

Flowering time in the wild: Throughout the year.

Distribution: New Guinea.

Distribution in New Guinea: Papua and Papua New Guinea: widespread.

Map: RIGIDMAP.JPG [Dendrobium rigidifolium Rolfe (including Dendrobium rhomboglossum J.J.Sm. and Dendrobium acutisepalum J.J.Sm.), distribution map, redrawn from P. Cribb, Kew Bull. 38 (1983) 267, map 5.]

Notes: Dendrobium rigidifolium is a widespread orchid in the mountains of New Guinea. It is vegetatively rather variable, field studies having shown that much of this variability in stature and leaf shape and size is dependent upon the exposure to which plants are subjected. Those growing in shade on trunks of trees such as Nothofagus are generally large with large elliptic leaves. Plants from more exposed situations (such as seems likely with the type collection) are more stunted and have smaller subcircular leaves.
(after Cribb, 1983).

Contrary to Cribb (1983) we consider that Dendrobium rhomboglossum and Dendrobium acutisepalum are not sufficiently distinct to uphold them next to Dendrobium rigidifolium. In particular, we found the angle of the mentum with the ovary, supposedly an important character, to be variable, even on the same individual. Specimens from the western part of the area tend to have smaller flowers on longer, more erect inflorescences than those from the eastern part.

Dendrobium terrestre is rather similar, but differs in that the callus ridges on the lip do not extend to the base of the midlobe as in Dendrobium rigidifolium.

Cultivation: Cool growing epiphyte, keep in shade.