Variations in topography, rainfall, and vegetation cover provide an almost endless range of habitat for plants and the orchid flora, having adapted to these various conditions, is extremely diverse. Generally speaking, each major type of habitat has its own orchid flora. Some species are widespread in area of similar habitat, others are confined to a very restricted locality.
The savannahs and grasslands have few orchids. Trees of the stands, small islands and lowland swamps are hosts for numerous epiphytic species (i.e. those which grow upon other plants or trees), mainly of the genera Dendrobium (particularly of the section Spathulata), Bulbophyllum, Acriopsis, Luisia, Diplocaulobium, Flickingeria, Cadetia and Oberonia.
The rain forests are the home of terrestrial genera (i.e. those which are rooted in the soil) Acanthephippium, Apostasia, Calanthe, the genera of jewel orchids, Cryptostylis, Cymbidium, Dipodium, Habenaria, Liparis, Malaxis, Nervilia, some Phaius, Corymborkis, Plocoglottis, Tainia, Tropidia and Vanilla.
The trees of the rain forests are hosts for species of many genera. These plants prefer the upper part of the trees, where light and air movement are sufficient for their growth. Consequently, they are rarely seen. The cloud forests, moss forests and subalpine areas often have orchids in great abundance. Here Aglossorhyncha, Bulbophyllum, Ceratostylis, Dendrochilum, Dendrobium (especially of the sections Perilous, Calyptrochylus and Oxyglossum), Diplocaulobium, Epiblastus, Eria, Guilianettia, Glomera, Glossorhyncha, Liparis, Mediocalcar, Oberonia, Pedilochilus, Phreatia and Taeniophyllum reach their greatest development.
Dendrobium and Bulbophyllum have attained an almost fantastic development of species in New Guinea, there being over five hundred in each genus. Species of these genera can be seen at almost any altitude in a wide range of habitats. Genera with over fifty species, some occurring at almost all altitudes, are Liparis, Malaxis, Oberonia, Phreatia and Taeniophyllum. Other genera with numerous species adapted to a wide range of altitudes are Agrostophyllum, Appendicula, Cadetia, Calanthe, Ceratostylis, Diplocaulobium, Eria (and Trichotosia) and Habenaria (including Peristylis). Glomera, Glossorhyncha and Mediocalcar, each with a number of species, are mostly confined to relatively high altitudes. Microtatorchis, although represented by twenty-three species, is rarely collected.
Some genera, which are very commonly found, are represented by only one or comparatively few species. Acriopsis has only one representative, A. javanica var. nelsoniana. This plant is a very common epiphyte at low or moderately low altitudes in New Guinea, particularly on the trunks of coconut palms. Coelogyne, six species, are usually large and conspicuous plants, quite common in some areas, and found under conditions varying from grassland to rain forest or denuded sites such as the gold workings at Edie Creek and from the coast to moderately high altitudes. Dipodium includes three species, of which D. pandanum, a large conspicuous climbing plant, is relatively common in some areas. This species extends from the islands off the coast to about 4,000 feet. Epiblastus, eleven species, and Giulianettia, seven species, are common plants of the higher altitudes. Grammatophyllum includes two species (we now recognize 3 species, ed.). G. scriptum is a common plant on Bougainville and throughout the Bismarck Archipelago. G. papuanum, a very large and conspicuous epiphyte with large inflorescences, is wide-spread at altitudes from sea-level to about 4,000 feet. Luisia, is represented by two species, one of which, L. beccarii is a very common lowland plant in New Guinea. Phaius includes three species, of which P. tankervilliae is a common plant in many grassy swamps at moderate altitudes and P. montanus a rather common terrestrial in some well-drained forests at altitudes between 3,000 and 5,000 feet. Pholidota is represented by four species, one of which, P. pallida, is a common and conspicuous epiphyte at moderately low altitudes. When not in flower, this species is often mistaken for a Coelogyne. Pomatocalpa is represented by four species, of which one P. marsupiale is common at moderate altitudes. Spathoglottis. is represented by fourteen species. These are common in open areas, either grassland, old roadside cuttings, banks of streams or even openings in rain forest at any altitude from sea-level to 9,000 feet.
The affinities of the orchid flora are certainly with that of the Indonesia-Malaya region rather than with that of Australia. The Australian connection is not very great but in the Highlands and in the savannahs of Papua there are a few representatives of typical Australian genera such as Pterostylis, Thelymitra, Calochilus and Spiculea. On the other hand, the bulk of typical Malayan genera are represented in New Guinea. At least thirteen species, of almost as many genera, such as Calanthe triplicata, Phaius tankervilliae, Pholidota pallida, Corymborkis veratrifolia and Eulophia zollingeri have a distribution from Asia to Australia.
Many orchids have considerable horticultural potential, the most important genus in this regard, undoubtedly being Dendrobium. The section Ceratobium of that genus is possibly the foremost group, with a number of species becoming popular in cultivation and as parents in hybridization programmes. Some members of this section can be crossed with sections Phalaenanthe and Latourea. Repeated sectional and intersectional, crossing and back crossing has almost limitless possibilities. Prominent among the species of section Spathulata are D. antennatum, D. gouldii, D. lineale, D. cochliodes, D. discolor (syn. D. undulatum), D. conanthum, D. lasianthera, D. schulleri, and D. nindii (syn. D. toftii and D. ionoglossum) D. tangerinum, D. helix, D. wulaiense.
Latourea, a section of Dendrobium, is almost as popular as Spathulata. Species such as D. atroviolaceum, D. johnsoniae, D. spectabile, D. bifalce and D. macrophyllum and others have proved suitable for hybridizing. Other species which are rapidly gaining in popularity are the those in section Oxyglossum. These sections include diminutive plants with large showy flowers. Species such as D. cuthbertsonii with a range of flower colour from cream and puce to deep crimson immediately become firm favourites whenever seen by orchid growers. Flower size is also very variable. Dendrobium williamsianum (section Phalaenanthe, ed.), a little known species of uncertain affinities, has relatively large, very pale-mauve flowers and a labellum with a dark mauve throat.
Genera other than Dendrobium which have horticultural potential are Acanthephippium papuanum, some of the larger flowered Bulbophyllum, Ascoglossum calopterum, Calanthe engleriana and C. chrysantha, almost all species of Coelogyne, some of the larger flowered species of Diplocaulobium, Dipodium pandanum, Grammatophyllum scriptum and G. papuanum, Macodes sanderiana, Paphiopedilum violascens, all of the species Phaius, Phalaenopsis amabilis var. papuana, Renanthera edelfeldtii, Sarchochilus moorei, almost all species of Spathoglottis, Thrixspermum amplexicaule, Vanda hindsii and possibly members of the Vandopsis-Arachnis complex.
With the exception of the saprophytic species (i.e. that live on decayed organic matter) in the genera Aphyllorchis, Corybas, Didymoplexis, Dipodium, Epipogium, Galeola, Gastrodia and Lecanorchis, for which successful cultural methods have yet to be devised, almost all other orchids have an appeal to enthusiasts, whether their particular interest is botanical or the cultivation of the beautiful or the unusual.
Paphiopedilum violascens merits a special mention because of the revival of interest in the genus in recent years. The flowers are only moderately attractive for the genus. Colour is variable, as also is size (particularly of petals and dorsal sepal), disposition and shape of petals. P. zieckianum and P. wentworthianum are probably synonymous with P. violascens. Distribution is extremely sporadic. It has been recorded from a very few localities at altitudes from about 2,500 to 4,500 feet (possibly extending to 6,000 feet), and the ecological conditions necessary for its survival are apparently very stringent.
The vast national heritage of orchid species, particularly of such genera as Paphiopedilum, will, in the near future, need to be protected by farsighted legislation. The increase in cattle raising, with the consequent clearing of large areas of forest for pasture, will be one of the most important factors in destruction of habitats. Use of steel axes has now made it comparatively easy to cut down large trees, often the hosts of many orchids. Before the advent of steel, these were often left standing in the garden areas. Unnecessary clearing and burning is sometimes undertaken. The increase in coffee, tea and forest plantations and other land-absorbing industries will mean a continuing decrease in natural forest. If orchids and other plants are to be preserved for posterity, large national parks and reserves in a comprehensive range of altitudes, forest types, etc., must be established without delay. Indiscriminate collecting, by both professional and amateur collectors and outright exploitation must be discouraged by legislation. The demands by growers for plants of New Guinea species and for hybrids with New Guinea parents can be met by the production of seedlings raised in flasks under sterile conditions. Plants so raised are free from the risks of disease and more readily grown in artificial climates, and so the day of indiscriminate orchid plant collecting has gone forever.
Neville H.S. Howcroft