Durabaculum tangerinum

The following article was written for the Orchid Species Bulletin published by the Orchid Species Society, which is based in Brisbane, Queensland in November 2003, and modified December 2024.
Bear in mind that any cultivation notes refer to the subtropical conditions of Southern Queensland, Australia.

Durabaculum tangerinum (P.J.Cribb) M.A.Clem. & D.L.Jones was first described by Phillip Cribb as Dendrobium tangerinum P.J.Cribb in the Orchid Review in 1980. It had been known in cultivation for more than 20 years as Den. “Tangerine” before being formally described. The specific epithet comes from the Latin tangerinus (tangerine-orange), referring to the orange-tan flowers.

Recent morphological and molecular studies show that the generic limits of Dendrobium need to be reviewed. Based upon these studies, Mark Clements and David Jones transferred Den. tangerinum to the genus Durabaculum in the Orchadian in April 2002. The generic name comes from the Latin durus (hard) and baculus (stick, staff), referring to the tough, elongated pseudobulbs.

Genera Orchidacearum 6 (2014) and the Plants of the World Online [POWO] take a broad view of Dendrobium, and prefers to maintain Durabaculum as part of Dendrobium section Spatulata. I prefer a consistent taxonomic classification of Orchidaceae, which does not rely predominantly on DNA and genetic information. Instead, I prefer to acknowledge ecology, pollination biology, breeding behaviour, as well as plant habit and floral characteristics. I recognise Durabaculum  as distinct from Dendrobium.

Durabaculum are large to very large, sympodial, epiphytic plants, which produce long, cane like stems. The stems bear many, alternating, two-ranked leaves in the upper two thirds. Its leathery leaves are permanent, unlike Dendrobium s.s., where the leaves are annually deciduous. Long, multi-flowered racemes are produced from the upper nodes of the matured stems. The waxy, resupinate flowers of Durabaculum have similarly shaped sepals and petals. In addition, the distinctly 3-lobed lip, has a basal mentum or spur, and also bears longitudinal calli on the disc. The majority of the species of this genus have wavy or twisted sepals and petals. Durabaculum are incapable of producing viable progeny with Dendrobium.

Du. tangerinum produces erect, cane-like stems that are slightly swollen in the lower third, which are 25-50 (-85) cm long and 1-2.5 cm in diameter. The stems bear many, alternating, two-ranked, thick, stiff leathery, oblong or oblong-elliptic, obtuse leaves that are 5-9 cm long and 1.5-3.2 cm broad along the upper half. Its leaf-sheaths that surround the stem are green-brown, and often striped or suffused maroon to purple, particularly when grown in bright light. One to several, erect to spreading inflorescences are produced from the upper nodes opposite the leaves. The racemes are up to 35 cm long, and are laxly few to 15- (20-) flowered. Each stem may bear up to 15 inflorescences over several blooming seasons.

The flowers of Du. tangerinum open widely, and have a tendency to somewhat nodding. They are 3-3.5 cm across and 4.5-5.5 cm high. The showy blooms are yellow to orange-yellow to orange-red speckled or striped with maroon or red-brown on the sepals and petals, which are usually much twisted and spiralled. The lip is red-brown to yellow, with red, brown or purple veins on the side lobes and purple to lilac or white veins on the midlobe, with 2-4 white and lilac-tipped ridges. Long-lived, the flowers last for 6-9 weeks. Flowering occurs year-round in its natural habitat, but in cultivation is usually from winter to spring.

An epiphytic or sometimes lithophytic plant, Du. tangerinum is distributed inland in the eastern provinces of Morobe and Madang in Papua New Guinea. It grows in the crowns of forest trees near rivers up to 250 m altitude, but may be found growing on rocks in regions of landslides at over 1,200 m elevation.

A warm- to intermediate-growing species, Du. tangerinum does best with a winter minimum of 15 ^⁰C, but will tolerate slightly lower temperatures for short periods, if the leaves are dry at night. It requires bright light, such as beneath 50-70% shade cloth, and a well-drained medium, high humidity, with good air circulation. Water it often during the warmer months, while the root tips are green and active. Give it a slightly drier winter rest, when the roots are no longer growing. I recommend some overhead protection for this species in the southeast Queensland region during the cooler months.

References:

Clements, M.A. & D.L.Jones. (2002) “Nomenclatural Changes in the Dendrobieae (Orchidaceae) 1: The Australasian Region.” Orchadian 13 (11): 484-497.

Cribb, P.J. (1986) “The ‘Antelope’ Dendrobiums.“ Kew Bulletin reprint. Royal Botanic Gardens, Kew.

Lavarack, P.S., Harris, W. & Stocker, G. (2000) Dendrobium and its Relatives. Kangaroo Press, East Roseville, N.S.W.

O’Byrne, P. (1994) Lowland Orchids of Papua New Guinea. National Parks Board, Singapore Botanic Gardens, Singapore.

Stearn, W.T. (1983) Botanical Latin. 3^rd ed. David & Charles Inc. Vermont, USA.

Pridgeon, A.M., Cribb, P.J., Chase, M.W. & F.N. Rasmussen. eds. (2014) Genera Orchidacearum, Volume 6: Epidendroideae (Part 3). Oxford University Press, Oxford.

Tkatchenko, J.W. & S. Kami. (2006) Spatulata Orchids Papua New Guinea. Orchid Society of Papua New Guinea Inc., Port Moresby, Papua New Guinea.