Evelyn Cheesman’s blue orchid

To discover a spectacular new orchid species that only inhabits remote, jungle-clad islands, it is not always necessary to actually go to a remote, jungle-clad island. Sometimes a short ride on the London Underground is enough, which is how I discovered Dendrobium azureum.

While scanning through dried material of unidentified Dendrobium species from New Guinea, in the herbarium of London’s Natural History Museum, I came across two sheets on which were mounted some unremarkable-looking specimens. But when I read their type-written labels they turned out to be worth a closer look. 'Orchid growing on trees; flowers deep sky blue'. Deep sky blue flowers? Orchids come in all colours of the rainbow, but very few species have really blue flowers and most of these are Australian terrestrial species, such as Thelymitra crinita.

Epiphytic orchids (those that grow on trees or other plants) with pure blue flowers are extremely rare. Only a handful are known among some 17,000 epiphytic orchid species. No close relatives of the Dendrobium I had in front of me had blue flowers and this at once suggested that it might be an undescribed species, assuming that the colour information on the label was accurate. Looking again at the specimen I then noticed that the dried flowers had a strange bluish grey tint, rather than one of the many shades of brown usually seen in old dried orchid specimens. This seemed to confirm that the flowers really had been blue.

The labels also revealed that the specimens had been collected by one L.E. Cheesman on 17 June 1938 on the summit of Mt. Nok, an extinct volcano on the, indeed remote and jungle-clad, island of Waigeo, off the western tip of New Guinea.

Following my visit, I sent out a loan request to the loans officer at the Natural History Museum, to enable me to examine the two Cheesman specimens in more detail. It is common practice among the world’s major herbaria to send specimens on loan to each other, so that the relevant taxonomic experts can take their time to study them in detail. After a thorough examination, and comparison with the large collection of Dendrobium specimens in Kew’s herbarium, I reached the conclusion that Cheesman’s Dendrobium was indeed an undescribed species, although it is probably closely related to D. oreodoxa, a species from New Guinea with bright orange-scarlet flowers. I described it in 2013, naming it D. azureum (Schuiteman, 2013). 

As far as I can ascertain, D. azureum has never been collected again. Three researchers who have visited Waigeo Island in the past decade (Campbell Webb, Iwein Mauro and Sebastian Schmidt) informed me that they had not seen it. There are only a few peaks as high as Mt. Nok, which itself is about 880 m high, and it is possible that the orchid is restricted to this higher mountain habitat. If D. azureum really is endemic to the frequently cloud-capped summit zone of Mt. Nok, and possibly a few similar mountains on the island, collecting seeds and bringing the species into cultivation may be advised, to safeguard its existence in the long term.

The continued occurrence of D. azureum on Mt Nok will depend on its habitat and its ecological relationships, such as those with its pollinators, remaining intact. Its habitat may come under pressure from deforestation and forest fires, and may also be sensitive to climate change. Since Waigeo Island is situated in the most diverse marine ecoregion of the world, and is itself home to some conspicuous endemic wildlife, such as the Red Bird-of-Paradise, strict protection of its remaining forests seems urgently needed.

Nothing is known about the pollinators of D. azureum. Closely related species (D. oreodoxa, D. lawesii, D. subclausum etc.; see Schuiteman, 2013) are probably all pollinated by birds, in particular honeyeaters (Meliphagidae), but observations are scarce.

It is likely that D. azureum is bird-pollinated too, as the size and structure of the flowers are only slightly different from those of D. oreodoxa. Let’s hope that there is still a chance to find out.