Dendrobium stuartii Bailey
Neville H.S. Howcroft

INTRODUCTION: During one of my earlier field trips to the Western province I found a number of small orchid plants growing in a patch of gallery forest near the Bensbach river. I later identified this orchid as D. stuartii Bailey when I flowered it at Bulolo. I started searching other areas towards Weam and I located numerous patches of this species growing on both dead and live trees in similar situations. All these plants were growing in exposed situations and none had any leaves at the time.

On a second field trip to the province I travelled from Morehead down towards the coast to an abandoned village called Old Tonda village. Here our party crossed a tidal creek that flowed into the Morehead River and drove into a swampy area where I found many trees with rather large plants of D. stuartii (Fig. 2) growing on them just above the flood level marks on the trunks. These plants were less exposed than those which I found at Bensbach and the had plenty of foliage.

The plant superficially resembles D. aphyllum (previously known as D. pierardii). It is one of four representatives of the section Dendrobium in Papua New Guinea, two of these appear to be new species.

DESCRIPTION: D. stuartii F.M. Bailey in Proc. Roy. Soc. Qld. 1:12, (1884); Callista stuartii (F.M. Bail.) Kuntze, Rev. Gen. Pl.2, 655, (1891); D. viridicatum Ridl. Journ. Str.Br. Roy. As. Soc. 39:72: (1903); D. tetrodon Reichb. f. ex Lindl; Ridley, 45 (1924) (p.p.); Holttum, 290 (1953); Comber, 17 (1983); Seidenfaden, 34, Fig. 13 (1985); 166, (1986a); Comber, 233 (1990); D. whiteanum T.E. Hunt, Qd. Nat. 14:60 (1951)

A pendulous epiphytic herb, stems c. 30 cm long, 3 -5 cm diameter, internode c. 1.5 cm long. Leaves lanceolate, c. 5.5 cm long and c. 1 - 2 cm wide, thin, acute. Inflorescence from nodes, bearing 1 - 3 flowers on short peduncles after the leaves shed. Flowers not always opening widely, ca. 2 cm across, frequently cleistogamous. Sepals lanceolate, acuminate c. 1 cm long, greenish white to pale yellow; petals similar but more acute; labellum as long as tepals, white with purple veins, pubescent except at the base, 3 slight keels at base, lamina more or less rounded with no distinct lateral lobes, margins fringed. Column short with or without a rostellum.

DISTRIBUTION: Far North Queensland, Australia to the southern part of New Guinea, extending into Java, Sumatra, Peninsular Malaysia and Thailand (Comber 1990, Seidenfaden & Woods, 1992). There is an unconfirmed report that it has been found as far south as the Eungella Range region near Mackay in Queensland.

HABITAT: Gallery forests near rivers creeks and swamps in the Western province of Papua New Guinea. Maximum altitudinal range appears to be 90 m.

View drawing: Dendrobium stuartii Bailey

Key to illustration: A - plant habit (5 cm scale), B - flower (10 mm scale), C - flower side view, D - dorsal sepal (10 mm scale), E - lateral sepal, F - petal, G - labellum flattened

NOTES: The flowers of the Bensbach collections match those illustrated by Comber (1990) and the illustration of the floral parts match those of Seidenfaden and Woods (1992). Comber described his as D. tetrodon and in their more recent publication, Seidenfaden and Woods retain the name D. stuartii stating that the other name belongs to a species close to D. aphyllum. Since D. stuartii, as I know it from Australian and PNG specimens, resembles D. aphyllum, it would be useful to know what D. tetrodon really looks like.

A number of PNG plants, that I have seen in collections in Port Moresby and in my own collection, are definitely cleistogamous. However several other plants in my collection have produced normal wide open flowers and on occasions some evidently self pollinated flowers on the same plant.

Dendrobium stuartii is the second of four species in Papua New Guinea which belong to the section Dendrobium (formerly Eugenanthe). The fourth appears to be a new species which I recently discovered at Itogama near the Managlase plateau in the Oro Province.

CONSERVATION STATUS: Although the plant is not uncommon where it has been found, it appears to be some what localised. The distribution of this species requires further study. For export purposes only flasked seedlings should be sent out of PNG.

REFERENCES:
Comber, J. (1990) Orchids of Java., Royal Botanic Gardens, Kew
Dockrill, A.W. (1969) Australian Indigenous Orchids.,The Society for Growing Australian Plants.