New Guinea Dendrobiums III: Section Pedilonum

The following article written by Richard Warren, has been reprinted from the American Orchid Society Bulletin, Vol. 59, No. 5, pgs 477-83, 1990. Additional images have been added and nomenclature and spelling conform to the World Checklist of Monocotyledons and published taxonomic descriptions.

As you climb from the swampy lowlands, home of the antelope dendrobiums, through the rainforest, so rich in Latouria species, you come to a sharply defined change in climate, habitat and flora. Depending on the area and the aspect, you may be at 2,000 feet or 9,000 feet above sea level, entering the moss forest. This is the orchidist's dream, so rich in plants and variety. But not only orchids drape the trees; myriad ferns, gesneriads and begonias drip from the branches, and each branch and trunk is completely coated with moss, giving it a unique little climatic world of its own. Schlechter was stunned by what he saw, and wrote of "the most bizarre forms" and "orchids . so numerous that I must restrict myself to the mention of genera!" There were too many species to recount! He concluded that this was the orchid collector's true paradise, richness was not to be found anywhere else in the world.

The high moss forests (left) of Papua New Guinea are an orchidist's dream, draped as they are in so many species of Pedilonum dendrobiums such as D. calyculimentum(right). Photographs copyright the Edinburgh Botanical Garden and Richard Warren, respectively.

The plants of section Pedilonum are part of the moss forest; the vital clues to growing them lie in a study of this unique habitat. The section is larger than those looked at so far in earlier articles; in fact it is the largest of the horticulturally attractive sections from New Guinea. Van Royen (1980) estimated that 45 species comprise the section, and Dockrill (1969) suggested there were 40; but a recent conversation with Phillip Cribb revealed there may be as many as 100 species, half of which belong in New Guinea. It is a widespread section, with representation in India, Burma, the Philippines, Samoa and Australia, but, once again, the center of development is in New Guinea. Some species such as D. secundum are quite well-known, while others such as D. bracteosum and D. smillieae are occasionally seen in nurseries. But these tend to be the lowland epiphytes from open forest and not moss forest.

Dendrobium pseudoglomeratum, widespread throughout Papua New Guinea and Irian Java at high elevations, has long-lasting, pink flowers with orange or orange-red lips. This specimen was grown by Don and Margie Crawford, Murryasville, PA; Photo courtesy of the AOS.

Generally, Pedilonum dendrobiums are bushy or pendulous epiphytic plants with moderately branched, reed-like pseudobulbs which have a slight swelling at the base. The fleshy stems have many nodes decorated along the length by sheathing leaves. Roots are usually thick but may be wiry. Inflorescences most frequently arise from the nodes of older leafless stems, breaking through the dried sheaths, but they may also come from the tips of younger leafy shoots. The short flower stems carry flowers that vary in color between specimens. Characteristically, the lateral sepals, which are larger than the dorsal, are fused to form a well-developed pouch or mentum, and the long, narrow lip is fused to the column foot, forming a spur-like nectary. Pollinia are in two pairs with a sticky viscidium which comes away from the pollinia quite easily but is very efficient at catching the pollinia when they touch again. The labellum is simple, often spade-shaped with only a hint of callus lines.

Species from the lower altitudes should be treated as Latouria dendrobiums in culture. They are fast growing, feed voraciously and form large specimen clumps (D. bracteosum, D. smillieae). But moss forest specimens are different and need very different treatment. The pendulous and creeping species have their roots and rhizomes on trunks and branches and are found growing out through the dense, mossy coat. Heavy rain is a daily event, and although there are bursts of intense sunshine on most days, the plants are in heavy shade. At night the entire moss forest is cloaked in mist until well after dawn, so, in fact, the plants never dry out. And even if keeping them wet presents hazards for the greenhouse grower, then at least the roots must never be allowed to become dry. Dry roots will guarantee the prompt kiss of death and another coffin in your orchid graveyard! Your plants look their best growing on bark or on tree-fern, but of course these can dry out easily, especially in a small greenhouse. Better to establish moss on your bark or tree-fern and wait until it is growing green before you tie on your specimens. This way you will be absolutely certain that you have created a microclimate in which your seedlings and plants will flourish. As long as the moss looks moist and healthy, you know your plants are in near optimal conditions. Cool-house temperatures, shade and good air movement complete the spectrum of needs by moss forest Pedilonum species.

Dendrobium smillieae 'Arabella', HCC/AOS grown by Diane and Neil Booth, West Hills, CA; Photo copyright Richard Clark.

Lowland Species

Dendrobium smillieae is the familiar "bottle-brush" orchid that grows in Australia and extends into the lowlands of New Guinea. It is a robust epiphyte and forms large clumps from 15 inches to 1 yard high. New shoots are covered with slightly contorted leaves which last for one season and then fall, leaving the old, thin leaf sheaths covering the brown, mature stem. Inflorescences arise at the uppermost nodes, and each raceme may have up to 100 flowers which are "upside-down" with the green, shiny lip uppermost. Overall, the flowers are white or cream-color with a pink mentum and pink tips on the petals and sepals. The lip and the lateral sepals form a nectary; access to this is through a tube. The species is widespread in the eastern tropics of Australia and New Guinea and is found growing epiphytically in open forest on bloodwood trees and other tree species with flaky bark. Large colonies reminiscent of cymbidiums in habit can develop in tree forks. It is a heavy feeder that is easy to grow in warm conditions.

Left, Dendrobium bracteosum var.album (represented here by 'Marge Smile', CCM/AOS grown by Lee Smile and photographed by Charles Marden Fitch), is the white-yellow form of the species, which is also red-flowered. Above right, D. alaticaulinum is a miniature species that flowers as early as two years out of flask. Photography by Norman Cruttwell. Lower right, D. roseipes is rare in cultivation but surprisingly easy to grow. Photography by Richard Warren.

Dendrobium ophioglossum (considered synonymous with D. smillieae by the World Checklist of Monocotyledons) grows both lithophytically (on rocks) and epiphytically in the New Guinea lowlands. The stems may be as short as two inches or as long as 14 inches and are stocky and fleshy with several nodes. There can be one or more pairs of leaves which are gray-green on the upper sides but distinctly purple-maroon on the undersides. Inflorescences are tufted and many-flowered with up to four inflorescences on each pseudobulb. Flowers are closely packed, all facing the same direction.

Each one is 1/2 inch long and colored white or cream, suffused with pale green, while the tips of the lateral sepals are a darker green. A small sac at the base of the lip forms an enclosed spur with nectar. This species is a good grower in normal bark-based compost or on moss-covered rocks. It was reported to occur in Australia, but an article by P. S. Lavarack (1980) suggests that the specimen found was probably a small D. smillieae. Dendrobium ophioglossum has also been confused with D. purpureum, a separate species distributed widely from the Malay Archipelago to Fiji (Lewis and Cribb, 1989), and can be distinguished from D. ophioglossum by its mauve-purple flowers and characteristic four-angled stem. Dendrobium roseipesis a delightfully exuberant plant almost unknown in cultivation (although it was first described by Schlechter in 1909 from 1,500 feet on Mount Gomadjidji on the Waria River). The stems reach three feet in length and have alternate leaves for all but the lowest nodes, which have papery sheaths and lead to a tapered base. When the leaves dehisce after a year, the green sheaths turn papery and eventually themselves fall, leaving the olive-yellow, hard stems marked only by the nodes and the scars of old inflorescences. Although flowering can occur at the two or so apical nodes of young canes, it is at its most prolific on the older leafless canes. A cane can have up to 10 tightly clustered inflorescences, each with as many as 30 flowers. Sepals and petals are uniformly pink, with their tips and the anther caps so white they look as if they have been dipped in paint. There is a distinct mentum, and in this lies nectar in the pouch made by the lip joined to the column-foot. Fast-growing and astonishingly prolific in flowering, this is as easy to grow as D. lawesii, a much-prized species for New Guinea enthusiasts. Dendrobium bracteosum is superficially similar to some of the Oxyglossum section species in that it has long-lived, colorful flowers with a marked, pointed orange lip. It is a rainforest epiphyte which grows to about 16 inches high. Its dark green leaves are tough, thin and pointed. Flowers are produced in dense clusters at the nodes, and the leafless stems may flower repeatedly for many years. Each flowering can last up to six months. Dendrobium bracteosum is found at 1,500 feet and above. Both color forms of rose-red and white-yellow are quite widespread. On Rossel Island, moreover, large, dark red forms are found in abundance growing epiphytically on mangroves.

Above left, D. dichaeoides is so-named for the resemblance of its leaf arrangement to that of the orchid genus Dichaea. Photography by Richard Warren. Lower left, D. aurantiroseum produces 10-20 flowers per cluster, photography by Richard Warren. Right, D. purpureum resembles D. ophioglossum but is distinguished by its mauve-purple flowers and four-angled stem. Photography by David Menzies.

Moss Forest Species

Dendrobium alaticaulinum is one of the most delightful miniatures with dark green leaves and slender, branched creeping stems. It soon forms a compact diminutive colony on a piece of tree-fern and flowers two years after deflasking. Van Royen (1980) describes a much longer-stemmed, thinner-leaved variety from 9,000 feet, but such forms are rarer in cultivation than the neater smaller varieties. Stems are covered with sheathing leaves and are only five inches or so long, and the plant produces small inflorescences of 3-8 flowers which are orange-pink, fading to white at the tips. They are, however, quite variable, and white and deep red forms are known. Norman Cruttwell (1989) describes a specimen which had "tassels of white to mauve flowers" with scarlet tips. Like most specimens in the section, there is a spur, and the pointed lip has five nerves. Margie and Don Crawford (1986) suggest that it is easy to grow.

Dendrobium dichaeoides could well be called the heather orchid because of the dense heads of heather-pink-purple flowers which are produced at the tips of the leafless stems. Easy to establish, the fine seedlings soon broaden out in 1/4-inch thick, fleshy stems with wide, blue-green, overlapping and alternate leaves which are quite reminiscent of the American Dichaea species after which it is named. Like D. alaticaulinum, it is a creeping plant, setting it apart from other species of the section, which are erect or pendulous. The well-branched pseudobulbs are firmly attached to the mossy substratum by thin, white, orange-tipped roots. Smaller plants (and they can be quite variable in size) have overlapping pseudobulbs, the oldest, leafless ones on the underside of the plant and the younger, leafy shoots on top, often tinged red where they have been exposed to the sun. The margin of the leaf is toothed towards the tip, and the tip itself often has a cleft. A fast grower, Dendrobium dichaeoides is found at over 3,000 feet above sea level. Seedlings soon grow to produce a lush green mat. At first, if they are on a raft of tree-fern, they grow upwards until a full-sized stem is produced; then the shoots turn and tend to grow pendulously. The flowers, often produced twice a year, are a joy and last for two months or more. The main flowering time is December to February in the Northern Hemisphere.

Dendrobium calyculimentum 'Sean', CBR/AOS grown by Lucien Tempera, Copaigue, NY; Photograph copyright Charles M. Fitch

Dendrobium calyculimentum colonies are formed from a number of thin, rope-like pseudobulbs about 6-10 inches long, although larger forms with stems up to a yard in length are known. The young growths have alternate leaves which point toward the ground, and the bases surround the stems with sheaths. The stems are frequently branched, and each stem has a faintly zigzag form. Its distinctive flowers are 3/4 inch long in lax clusters of 5-15, which are colored white to pink with red anther caps. The long pointed sepals and petals are curled back at the tips. Although flowering occurs from the nodes of the older leafless stems, it also happens occasionally toward the tip of the younger leafy stems, too. The roots of D. caliculimentum are fine and wiry, unlike most other species in the section, and form a pad of hessian-like material.

Dendrobium aurantiroseum (known to some as "Aunty Rosie") differs from many of the species in having almost globose young pseudobulbs, unlike the reed-like stems more frequently found in this section. The red-brown pseudobulbs are separated by a thick rhizome covered with papery bracts. The bulbs have two or three swollen internodes tapering to another two to four nodes at the tip. There are a pair of gray-green, finely pointed leaves which have a reddish tinge marked with fine parallel lines on the underside. There is a definite midrib. This plant has few roots, but those it has are thick. The flowers, which are sometimes so prolific as to conceal the plant, are produced on clustered inflorescences with 10-20 flowers per cluster and 2-4 clusters per bulb. Flowers are quite flat and pink with a long spur. The lip is heart-shaped and tinged a deep red along its length. Flowering occurs in December to February, and flowers last for about a month in the shade.

Dendrobium womersleyi is a pendulous epiphyte with wiry and almost woody old stems with a slight zigzag along their length. It may grow to a yard in size. The leaves are pointed and alternate over the full length of the young growths, and they are retained at the top of the stem for the following year. After dehiscence, their bases turn a deep maroon-brown. Branches occur quite often, and the roots are thick and fleshy. Buds break through the dried bracts and then open to broad, orange flowers. One to three flowers are produced at each node in an extended sequence, and although each flower lasts only for about three weeks, the flushes of flowering can last for months. A cool grower from high elevations, this plant's seedlings have proved a challenge to culture, but once past the danger stage in flasks they are easy to establish.

Dendrobium rarum is a shy creature, being as rare in nature as the name would suggest. It is also sometimes modest in its flowering, since it can be self-pollinating, with the result that the flowers disappointingly set seed before they have even opened completely. It occurs in nature only in isolated pockets, and even then often as solitary specimens. It is found in New Guinea and eastward in the islands as far as Vanuatu. The fine stems are 15-18 inches long and taper over the lower few inches to a slightly swollen base. They are also ridged along their length and are purplish on the upper surface where they are exposed to direct sunlight. The thin leaves are four inches long. Flowering occurs at the apical nodes, with a sparse inflorescence of 3-15 flowers which are rose-red with white tips and have a fringe of fine hairs on the petal tips. From 3,000-4,000 feet, it is cool-growing, but not much is known about culture from the few existing specimens. The island forms from lower elevations are warmer growing.

Dendrobium chrysoglossum 'Marge Soule', CHM/AOS, grown by Lee Soule; Photograph copyright, Charles M. Fitch.

Dendrobium pseudoglomeratumis a startling New Guinea species about which there has been some confusion. It is shown twice on page 40 of Andree Millar's book (1978) under D. glomeratum and D. chrysoglossum. The confusion over the three species was finally sorted out by Reeve and Wood (The Orchadian, vol.1,113) where D. pseudoglomeratum was first described. It is a robust epiphyte with stems reaching one yard and with slight swellings at the stem bases. The thin, dark green leaves are produced along the stem's length, and the older stems are covered with papery, dry leaf sheaths. The many-flowered inflorescences are produced from the topmost nodes of the older stems (arranged rather likeD. smillieae), with the orange or orange-red lips uppermost and the soft pink petals and sepals underneath. It can be found flowering at any time of the year, and each flush lasts for up to two months. It is quite widespread in Papua New Guinea and Irian Jaya where it is found over a range of 3,400 to 5,500 feet elevation. It differs sharply from D. glomeratum in three ways: it has a triangular rostellum, it flowers from the leafless stems only and it is many-flowered.

Literature Cited

  • Crawford, D., and M. Crawford. 1986. Growing some Pedilonum Dendrobiums. AOS Bull. 55: 788-791.
  • Cruttwell, C. N. 1989. Orchids of Mount Gahavisuka - Part Two: Dendrobium. The Orchadian 9: 144-147, 160-162.
  • Dockrill. A.W.I 969. Australian Indigenous Orchids. I. The Epiphytes. Halstead Press, Sydney.
  • Lavarack, P. S. 1980. The True Identity of Dendrobium ophioglossum. The Orchadian 6: 212.
  • Lewis, B., and P. Cribb. 19X9. Orchids of Vanuatu. Royal Botanic Gardens. Kew, London.
  • Millar. A. [978. Orchids of Papua New Guinea. Australian National University Press. Canberra.
  • Schlechter, R. 1982. The Orchidaceae of German New Guinea. (English translation) Australian Orchid Foundation, Victoria, Australia
  • van Royen, P. 1980. The Orchids of the High Mountains of New Guinea. J. Cramer. Vaduz.