Dendrobium cuthbertsonii F.Muell., Trans. & Proc. Roy. Soc. Victoria 24 (1888) 175.
Type: Cuthbertson & Sayer s.n. (holo MEL, iso BRI, K).
Epiphyte, or occasionally terrestrial, 2-8 cm high, usually tufted and clump forming sometimes to 12 cm diameter, or occasionally forming loose, sometimes shortly branched, prostrate or ascending stems. Roots 0.5-1.5 mm diameter. Rhizome short, or often elongated if growing in thick moss or in heavy shade. Pseudobulbs 0.5-8(-14) by 0.1-0.7 cm, spheroid, ovoid or clavate, sometimes stem-like and then sometimes shortly branched, branches 0.6-2.5 cm, 2-4 noded (or many noded on long-stemmed forms); 1-5-leaved, leaves more or less terminal, sometimes many and then scattered along elongate stems, erect or spreading or occasionally at almost right-angles to stem. Leaves 0.5-4.2 by 0.075-1.5 cm, linear to broadly elliptic or, if short sometimes ovate, upper surface glabrous to densely verruculose-papillose, warts or raphids sometimes confined to apical part or margins, sometimes sparsely warty, apex obtuse or acute, shortly petiolate or not; sheaths membranous, ribbed, verruculose or not, persistent, sometimes becoming fibrous. Inflorescence 1-flowered, terminal, rarely lateral on plants with elongated stems, bracts (1-)2.5-9 mm long, finely verruculose or glabrous, membranous, tubular or cup-shaped, ovate acuminate. Flowers 2.2-4(-5) cm long to c. 3.3 cm wide, pedicel very lax so as to cause the flower to sit horizontally or pendulous with lip uppermost, rarely sub-erect. Median sepal 10-21 by 3-12(-15) mm, oblong to broadly elliptic, obtuse. Lateral sepals 18-30(-34) by 4-12(-18) mm, oblong to broadly elliptic, sometimes broadly triangular, apex obtuse, rarely acute; fused basal part 4.5-8(-11) mm, narrowly cylindrical; mentum total length 9-18 mm, tip obtuse. Petals 10-20 by (3.5-)6-16 mm, obovate to rotundate, obtuse. Lip 12-30 by 5-15 mm (when flattened), obovate adnate to column foot at base, margins strongly upcurved, inside concave, finely or sparsely muriculose or glabrous, floor sometimes thickened fleshy, with or without a transverse V- or U-shaped ridge near base. Column 5-7 mm long to 5 mm wide; foot 9-18 mm long; anther c. 3.5 mm, broad; pollinia c. 2 mm long. Ovary indistinctly 6-ribbed, not angled, densely or sparsely papillose-hirsute or verruculose or glabrous; pedicel and ovary 10-32 mm long. Fruit to 20 by 10 mm, obliquely ellipsoid with 6 low verruculose or papillose-hirsute longitudinal ribs of unequal width and 6 narrower alternating glabrous furrows.
(after Reeve & Woods, 1989).
Colours: Roots white, often pinkish to purplish when wet, tips green. Leaves green to blackish green, lower surface often purplish or purplish veined; sheaths pale green sometimes black towards base. Flowers commonly red (scarlet to crimson), lip sometimes paler, with darker, reddish brown marks on margin, or flowers purple, pink, orange or less commonly yellow or white, sepals and petals self-coloured or, not infrequently, strikingly bicoloured, the apical parts paler or contrastingly coloured.
Habitat: Epiphyte, occasionally terrestrial or lithophytic, on shrubs, tree ferns, moss forest edges and ridges, Nothofagus, mossy rocks of streams, road cuttings, exposed cliff faces, semi shade or in open areas often exposed to breezes. Altitude 750 to 3450 m.
Flowering time in the wild: Throughout the year. Individual flowers may last up to eight months.
Distribution: New Guinea, Bismarck Archipelago (New Ireland).
Distribution in New Guinea: Papua (Vogelkop Peninsula, Wandamen Peninsula, Cyclop Mountains, Central Mountain range); Papua New Guinea (Sandaun, Enga, Southern Highlands, Western Highlands, Simbu, Eastern Highlands, Madang, Morobe (including Umboi (Rooke) Island), Oro, Central and Milne Bay (including Goodenough Island) Provinces; New Ireland).
Map: CUTHBMAP.JPG [Dendrobium cuthbertsonii F.Muell., distribution map, redrawn from T.M. Reeve & P.J.B. Woods, Notes Roy. Bot. Gard. Edinburgh 46 (1989) 290, map 18.]
Notes: Dendrobium cuthbertsonii is undoubtedly the most popular of all New Guinea orchids in cultivation. It is notable for its relatively enormous flowers and for the almost unparalleled range in colour forms. The long-lived flowers are not resupinated: the lip is held uppermost. Even without flowers this species is usually highly characteristic because of the glistening warts that normally cover the upper surface of the dark green leaves. Similar types of warts, or longer papillose-hairy ones, also occur on the pedicels and ovaries. On the other hand, specimens with glabrous leaves and ovaries are known to occur. Plants are normally compact with distinct pseudobulbs, but specimens growing in the shade may have slender, branching stems, as illustrated for Dendrobium agathodaemonis, one of the many synonyms.
The presence of a thickened transverse V- or U-shaped ridge inside the lip near the base was noted and illustrated by Smith when describing Dendrobium asperifolium and Dendrobium lichenicola and by Schlechter for Dendrobium trachyphyllum but not for any of the other synonyms nor the type. This feature is not easy to see in herbarium specimens and is easy to miss in living material, and may indeed not always be present.
Reeve (1978) noted that red-flowered forms of D. cuthbertsonii probably predominate throughout the species range: in some localities there may be a greater incidence of other colour variants. Further field observations and genetic studies are necessary to determine whether any pattern of colour inheritance or colour distribution exists.
Nothing is known of the pollination of this species, but there can be little doubt that D. cuthbertsonii is pollinated by birds (in particular Meliphagidae ). As the flowers do not produce nectar it seems likely (at least to us, Schuiteman & de Vogel) that they imitate other ornithophilous flowers, in particular Rhododendron species, growing in the same habitat. The striking colour-polymorphism exhibited by D. cuthbertsonii may serve to prevent the birds from becoming alert to the impostor.
Cultivation: This cool growing species should never be allowed to dry out, yet soggy conditions should also be avoided. In nature in can grow in open positions, fully exposed to the burning mountain sun, but in a greenhouse strong sunlight would quickly lead to desiccation and death. It seems that Dendrobium cuthbertsonii is unusually sensitive to pesticides and salt.
(in part after Reeve & Woods, 1989)