Orchidaceae of New Guinea
Introduction
The Orchidaceae of New Guinea represents the largest percentage of all known orchid species in the world with an estimated 3,000 species out of a total of some 30,000 known orchids species throughout the world. Research of the Orchidaceae of New Guinea since Rudolf Schlechter has been sporadic at best and the Orchidaceae of New Guinea is much less researched and understood than those of SE Asia or Central and South America.
The monumental work done by Rudolf Schlechter to this day provides the basis of all knowledge of the Orchidaceae of New Guinea and while other eminent authors have addressed individual genera and/or sections in a genus there is no complete account of all genera represented in New Guinea. The purpose of this Web site is to introduce you to all the orchid genera and species found on the island of New Guinea, both the eastern part, the Independent State of Papua New Guinea and the western part known as Irian Jaya, a province of Indonesia. It is hoped that with the details on this Web site you will be able to identify the genus of a New Guinea orchid and the species.
The success of the Orchidaceae within New Guinea and its adjacent islands is the result of adaptation. Although it shares species from adjacent regions, its wide range of diverse habitats has resulted in members of the family becoming specialised so that the country has become richly endowed with endemic orchids, many of which are horticulturally attractive or are of considerable botanical interest. Due to this the New Guinea orchids have been extensively exploited up to the present, but with little or no benefit to the people of the country.
A viable orchid industry has yet to be established in Papua New Guinea and orchid conservation is still in an unsatisfactory state in spite of efforts since 1990 to enforce the ban on the removal of adult plants from the country. Orchid research until now has been limited to taxonomic research done by visitors, some long-term residents and by a few private growers.
The need to establish an orchid industry and a flora conservation program is not being addressed due to lack of funds and a general apathy by the Papua New Guinea Government to recognise the importance of minor forest products. Sporadic efforts have been made by Government organisations such as the Forest Research Institute (FRI) but without sincere determination and actual allocation of funds and manpower the future of orchid conservation in Papua New Guinea looks grim indeed.
Orchids in Papua New Guinea are categorised as a minor forest product and they are considered a renewable resource, which can and should be utilised. However, New Guinea orchids have been collected by botanists and orchid collectors for more than a century and in spite of this very little is known about the conservation needs of most of the genera and species. This is due to inadequate information on their distribution, habitats and biology.
If the native orchids are to be utilised commercially then there is a need for a sound resource management policy for the orchids and other flora. Further there is an urgent need to determine the conservation needs of the species in the country and to identify and protect areas of special conservation significance.
Any attempt at conserving native orchid populations must take into account the critical factors that affect their development. Major threats to New Guinea orchids come from two main sources, the destruction of habitat and over-collection of certain species. Currently there have been reports that adult orchid plants are still leaving the country in spite of the ban to export native orchids.
As most of the land in Papua New Guinea has traditional landowners, the people must play a key role in conservation in the country. Because of this some conservation objectives may be achieved through economic incentives. Industries, based on the commercial utilisation of native flora and eco-tourism, may provide those incentives.
Research and development and public awareness and cooperation are required before these can be successfully established. Some activities have already started in that direction.
An orchid conservation project was designed several years ago to promote the protection of Papua New Guinea's floral diversity by establishing a gene pool for endangered species of orchids and other flora. It was intended to establish laboratory facilities for research support for the project and for the collection, storage and artificial propagation of plants. The project was to develop an export market for propagated plant species, conforming with CITES regulations, and it would have promoted and assisted the development of village based horticultural farms to grow orchids and other plants for the production of cut flowers and seed on a commercial basis.
The Orchid Family - Orchidaceae
The Orchidaceae are terrestrial, epiphytic or saprophytic herbs. Their flowers are zygomorphic with both sexual reproductive organs combined on each flower. Orchids have an inferior ovary and produce fruit capsules (pods). These contain numerous minute seeds from which the endosperm is absent. The Orchidaceae represent the highest level of specialization of the monocotyledons, which have a corolla. The Orchidaceae are divided into five subfamilies and these in turn are divided into tribes and subtribes.
Orchid classification is based on plant habit and structure of the the reproductive organs. There is considerable morphological diversity among the orchid subfamilies and tribes.
At the time of writing some 1,400 natural genera and hybrid genera and an estimated 30,000 species are recognized in the Orchidaceae. In New Guinea an estimated 3,000 species are found representing 134 genera. The island of New Guinea is the center of distribution for orchids in the genera Dendrobium and Bulbophyllum with more than 500 species each in both genera.
Orchid Habitats
Orchids are perennial herbs and according to their habitat are divided into terrestrials and epiphytics. Terrestrials are those which live in or on the ground and epiphytics are those which live on trees and have their aerial roots attached to the bark. Among terrestrial orchids are some which are defined as saprophytic, living on decaying matter, while among the epiphytics some are defined as lithophytic, living on rocks. So some extent this is a simplistic definition of orchid habitats as it is not uncommon in New Guinea to find epiphytic orchids growing in or on the surface of exposed soil (e.g. Dendrobium cuthbertsonii), like true terrestrials.
All orchids are further divided into to types of habits, monopodial orchids (growing on one foot) and sympodial orchids (growing on many feet).
Terrestrial Orchids: Terrestrial orchids are either creeping or erect in habit and can be divided into two types: the solitary type and those growing in clumps or tufts. Within the solitary type group of terrestrial orchids there are two kinds of growth habit; one with plants producing single, erect, leafy stems arising from underground tubers or corms which are terminated by an inflorescence. They are deciduous after fruiting and seeding are completed. The tubers or corms continue their life cycle after an annual period of dormancy. Orchids with the second type of solitary growth habit produce a flowering shoot and leafy shoot from separate buds on the rhizome. Genera such as Nervilia, Eulophia and Pachystoma are examples of this type. The erect terrestrials are usually evergreen, retaining their leaves for more than a year. Each new growth starts from the base of the leafy pseudobulbs as in the genera Liparis, Acanthephippium, Calanthe and Phaius.
The creeping terrestrial orchids have mostly slender, smooth, fleshy rhizomes with elongated internodes and several short or long roots at the nodes. Axillary buds, formed below the apex of the rhizomes produce and ascending leafy and flowering shoot. New annual growth is repeated at the end of flowering, fruiting and, in most cases, after leaf fall. The mother ascending shoot gradually becomes prostrate and becomes an additional part of the rhizome. Examples of orchid genera in New Guinea with this type of growth habit are Erythrodes, Eurycentrum, Eucosia, Hetaeria, Macodes, Vrydragzynea and Zeuxine. Epiphytic Orchids: Epiphytic orchids are distinguished by the presence of aerial roots which are used, apart from feeding, to anchor the plant to host plants or other objects. Epiphytic orchids are found growing on the bark of trees, on the surface of rocks and in certain conditions, as terrestrials on the face of road cuttings, in peaty soils of exposed bogs, mossy cushions, in tall grasslands and on the forest floor. In habit epiphytic orchids may be creeping or trailing or may have an erect habit.
In New Guinea, epiphytic orchids with a creeping habit are generally pseudobulbous however, there are those which have their stems spaced apart as can be seen in the genus Hippeophyllum, or in the section Rhizobium of the genus Dendrobium. Two types of creeping habit can be recognized among epiphytic orchids. The first type of two vegetative growths can develop from the base of the pseudobulb either simultaneously or over a period. The division of the plant is by pairs of new growths which produces a many-branched plant. This growth pattern is sometimes referred to as dichotomous. The dichotomous growth pattern is clearly seen in the genera Coelogyne, Dendrochilum and Rhynchophreatia. In the second type of creeping habit the orchid produces only one growth from a bud at the base of the pseudobulb. the first develops either a short shoot which will become a rhizome with a leafy pseudobulb, such as in Bulbophyllum, Diplocaulobium, Dendrobium and Eria, or the bud may develop into a flowering shoot which gradually will develop a rhizome and pseudobulb as flowering reaches its peak and fruit commences to develop. Pholidota species are good examples. This type of growth pattern is sometimes referred to as the straight-line type of creeping habit.
Epiphytic orchids with the trailing habit have elongated, leafy stems which require some form of support to which they anchor and prop themselves with long aerial roots. With some genera the stems elongate beyond the length of this support and become pendulous or sprawling. Examples of trailing orchids are Aerides, Arachnis, Cleisostoma, Phalaenopsis, Sarcanthopsis, Thrixspermum, Vanda and Vandopsis. Orchids with the erect, clumpy growth habit produce new shoots from the base of both fresh and old stems forming sparse to dense clumps. Examples of this habit are Dendrobium ventriloquism and Grammatophyllum papuanum.
The Orchid Family - Structure
Orchid Roots: The primary function of the roots is anchorage in epiphytic orchids. In structure the orchid root, longisection-wise, generally consists of six layers or zones: starting from the center, there are the stele, endodermis, cortex, exodermis, velamen and the root cap. The surface of the velamen may be smooth, rugose, pustular, pubescent or villose. In epiphytic orchids the velamen is silvery-grey, white or brown. In leafless (aphyllous) genera such as Taeniophyllum the roots are the only photosynthetic organs and contain chlorophyll which makes them green in colour. The feeding roots of orchids enable the plants to obtain nutrients through absorption from symbiotic fungi. the root caps of epiphytic orchids are generally green and sometimes deep red. In terrestrial orchids the root caps are usually smooth and white. The fleshy roots of many terrestrial orchids act as storage organs conserving food and water during the dry seasons and dormancy.
Orchid Stems: The stems of New Guinea orchids display a great deal of morphological diversity. They can be deciduous or they can persist for several years or indefinitely. Stem form determines the habit of the species and is important in the classification of orchids. Two main types of stem forms are recognized: monopodial and sympodial. Several types of monopodial and sympodial orchids are illustrated in Figure 1.
Monopodial Orchids: Monopodial orchids have a single, continuously elongating axis that enables the plant to grow in a trailing fashion over supporting plants or to form large, dense masses of vegetation. The monopodial stem is rarely adapted to water conservation however, it is capable of persisting indefinitely.
Sympodial Orchids:Two types of axes may be distinguished in sympodial orchids: a horizontal creeping rhizome giving rise at intervals to branches in an erect position, and upright fleshy stems or pseudobulbs. Unlike monopodial orchids, orchids with sympodial growth have a determinate type of growth whereby, after the production of a certain number of leaves, growth abruptly stops or is terminated by an inflorescence.
Orchid Leaves: In the orchids the arrangement (Fig. 3.3), size, shape and texture of the leaves reflect their habitats, habits and taxonomic positions. Most orchids have leaves, but here are some genera, both terrestrial and epiphytic, that lack leaves as for instance Aphyllorchis and Taeniophyllum. The leaves of the Apostasioideae subfamily are slightly thin, plicate-venose with a number of prominent parallel ribs on the underside of the leaves (Fig. 2.1); however, the leaves of the Cypridedioideae subfamily, and Orchideae, Neottieae and Arethuseae tribes, subtribes and alliances generally have soft, herbaceous, small to medium sized basal or cauline leaves without coarse veins (Figs. 2.2 to 2.8).
In the Epidendreae tribe the leaves are more diversified morphologically. The terrestrial genera such as Acanthephippium (fig. 2.9), Calanthe, Malaxis, Phaius and Spathoglottis have large plicate leaves that are thin, papery, and with parallel ribbing. The epiphytic genera such as Agrostophyllum (Fig. 2.10), Dendrobium (Figs. 2.16 to 2.18) and Oberonia (Fig. 2.14 to 2.15), have numerous leathery, small to medium sized leaves distichously arranged on the stem. Genera with creeping pseudobulbs such as Coelogyne, Bulbophyllum (Fig. 2.11), Diplocaulobium (Fig. 2.12 and 2.13), Eria and Pholidota have one to four leaves apical to the pseudobulb. In the Vandoideae subfamily the leaves of both terrestrial and epiphytic genera are also morphologically diversified. Among the monopodial epiphytes such as Arachnis, Micropera, Phalaenopsis, Rhynchophreatia (Fig. 2.19, Thrixspermum (Fig. 2.21) and Vanda (Fig. 2.20) the leaves may be medium to large in size and rather leathery and often fleshy.
In addition to the diversity in leaf characteristics, certain orchid genera and species may be recognized by their colourful leaves and venation. Genera such as Anoectochilus, Goodyera (Fig. 2.5), Corybas (Fig. 2.7) and Macodes are well known for their attractive leaves, which has given them the common name of 'Jewel Orchids'. The genus Trichotosia, formerly included as a section of the genus Eria, is noted for its hairy leaves and stems. The orchid leaf types, whether plicate, soft leathery, hard leathery or fleshy, are related to the plant's environment. They are a direct result of modification to enable the plant to cope with a specific habitat.
The primary function of plicateness in orchid leaves is photosynthetic, providing a large surface area for exposure to light, particularly in shady and moist situations. Plicate leaves are usually seasonally deciduous, and water retention, important to epiphytic orchids, is taken over by the pseudobulbs, fleshy roots and other underground structures.
The leaves of epiphytic orchids are usually leathery or fleshy to varying degrees and a waxy cuticle covers the laminas. Leaves such as these contain a considerable amount of storage tissue and are persistent for a number of years. The petioles are tubular and tightly envelop the internodes of the stem. An articulation between the lamina and the petiole sheath permits the lamina to be shed when it has aged and is no longer functional.
Orchid Flower Structure: The inflorescences are either as shown in Fig.3.1:
basal
- inflorescence produced from the base of the pseudobulb
auxillary
- inflorescence(s) produced from a node in the upper angle between the leaf base and the plant axis
terminal
- inflorescence produced from apex of the plant and terminating apical growth of the plant, and the flowers may be arranged as shown in Fig. 3.2:
umbel
- flowers or pedicels spaced along an unbranched lengthened axis
panicle
- flowers or pedicels spaced along branches of a compoundly branched lengthened axis
It is generally believed that orchid evolved from a primitive plant similar to the lilies and in the course of their evolution the structure of the various organs became considerably modified.
Although orchids display a considerable polymorphy and structural diversity, they all have a very similar floral plan. In Figure 4 floral diagrams of a typical monocotyledon, the lily , are compared with those of the primitive orchid Apostasia (Fig. 4 C,D) and an advanced orchid, Phaius (Fig. 4F).
The perianth of both lily and the orchid flower is arranged in two whorls, the outer with three sepals and the next with three petals (Fig. 4B, D and E). In most cases in the orchids, one petal is modified and is called the labellum (Fig. 4E and F).
The reproductive organs of the lily are clearly definable as separate organs, the style with the stigma and two whorls of three stamens, each bearing anthers containing pollen grains. These are indicated by the dark bodies in Figure 4 A-B . In the orchids the reproductive organs are considerably modified. The style and stigma are united in various ways to form a single structure, the column which contains the stigma, anthers and pollen. The column is illustrated in Figures 4F and G and diagrammatically represented by a three-quarter circle in Figures 4D and E. The location of the stigma is indicated by a triangle.
The three additional stamens which occur in the lily are never developed in the normal orchid flower. As in the lily the ovary of the orchid flower is always below the other parts of the flower, and it is constructed of three parts as can be seen in the cross section of the ovary (Fig. 4F/H). Each part contains a single longitudinal ridge upon which the seeds are borne. These ridges are called the placentae (Fig. 4H).
Variations in Flower Morphology
The simplest orchid flower is represented by Apostasia. The petals are all identical, it has two anthers and a simple style, stigma and ovary.
In the genus Paphiopedilum, the petals are somewhat modified, the lower petal or labellum forms a pouch. the column is modified, bearing two very short-stalked anthers, a shield-like plate called the staminode and a stigma.
(A staminode is a sterile anther, so two anthers and one staminode make up three parts of the staminal whorl.) Each anther contains two masses of sticky pollen.
In Habenaria the dorsal sepal and petals often form a hood over the column, the lateral sepals spreading the labellum with simple or ornate lateral lobes and medially terminating in a spur. the column is short, the two pollinia encased in anther cells separated by a rostellum and their caudicles encased in short or long tubes called thecal tubes. the stigma is prominent and modified into two parts (the stigma pores) and occurring on either side of the spur orifice.
In Pterostylis the dorsal sepal and petals form a hood. the lateral sepals are joined at the bases. the labellum is hinged to a short column foot and is mobile. the column is long and slender. the back of the column is joined at the base to the base of the dorsal sepal, apically with two wings on its ventral surface, each wing with one narrow apical projection at the top. the stigma is prominently placed on the center face of the column, well removed from the rostellum. The four pollinia recline inside a receptacle (called a clinandrium) protected by a modified anther.
Spathoglottis has a simple flower structure. the sepals and petals are more or less equal and spreading widely. The labellum however, consists of three lobes and has two prominent calli near the junction of the lobes. The column is slender and curved with a very short column foot; the pollinia recline in a clinandrium protected by the anther. The stigma is located on the central surface of the column just below the apex; a ridge (rostellum) separates the stigma from the clinandrium.
Calanthe has its sepals and petals more or less spreading freely. The sepals are usually larger than the petals and it has a branched labellum terminating in a spur. Labellum with calli, as in Spathoglottis. the column is short, joined throughout its length to the base of the labellum, with which it forms a tube. The pollinia also recline in a clinandrium protected by the anther. The stigma is divided into two parts above the spur orifice; these are separated from the clinandrium by the rostellum.
Aphyllorchis has sepals and petals about equal and free and a labellum with a distinct, short, narrow basal portion (the hypochilium), and a larger three-lobed extension (the epichilium), more or less hinged to the hypochilium. the column has a clinandrium, rostellum and stigma. Dendrobium has the lateral sepals joined over half their length at the base to form a prominent spur (tube or mentum). The column extends into a column foot. The column is short and equipped with stigma, rostellum and clinandrium. the pollen are protected by the anther. Not all species of Dendrobium have a similar flower structure.
ABulbophyllum has prominent, sometimes ornate sepals, small petals (which are sometimes ornate), a short column and column foot. The hinged labellum is small, mobile and often ornamented with hairs or warts.
Orchid Pollinia
In most cases the pollen of orchids is not powdery but united into small masses, called pollinia, each containing several thousand pollen grains. The type of pollinia is very important in orchid classification.
Habenaria has a large number of pollen grains massed together (collectively called a pollinium). The pollinium is attached to a slender extension, called a caudicle, which terminated in the viscid disc (an organ to help pollen dispersal, sometimes referred to as the retinaculum). In Goodyera the pollinia are divided, grooved and granular, often with a well developed viscid disc. In Vanda the two pollinia are large. Each has a cleft. The pollinia are connected to the viscid disc by a short, broad and flattened stipe. Dendrobium has four pollinia in two pairs. Stipes and viscid disc are usually absent.