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CONSERVATION AND REINTRODUCTION OF THE NATIVE ORCHIDS OF SINGAPORE
TIM WING YAM
Singapore is located at about 1º north of the equator, off the southern tip of the Malay Peninsula between the South China Sea and the Indian Ocean. It consists of the main island of Singapore, and 58 nearby islands. The total land area is about 690 sq km. The whole island consists of mostly lowland. The highest point is at Bukit Timah, reaching a height of 165 meters. It has an equatorial climate, with a relatively uniform temperature and high humidity. The average daily temperature fluctuates between 25.2ºC to 32ºC. Its annual rainfall is about - 1,700 mm, the wettest months are November to January.
Although Singapore is a modern city, there are many interesting types of natural habitats. In the heart of the main island is a primary rainforest and freshwater swamp forest. In addition, some mangrove also remain. The other habitats consist of secondary forests, shrub, grasslands and urban parks and fields.
In 1998, about 221 species of native orchid were recorded in Singapore (Keng et al., 1998). However, based on lists in a preliminary report on the conservation status of plants native to Singapore (Ng and Wee, 1994: Tan, 1995), more than 90% of the native orchids in Singapore are either endangered, vulnerable, rare or extinct. Therefore an orchid conservation programme was initiated to monitor these species and to attempt to find ways and means to conserve their germplasm and to increase their number for subsequent re-introduction into appropriate habitats in the nature reserves, parks and roadside trees.
Native orchids in Singapore can be divided into two main groups - epiphytes and terrestrials.
First, the epiphytes. No other genus could be better used to illustrate the epiphytes in Singapore than Dendrobium. Almost all the Dendrobium species are epiphytes. Dendrobium is the largest genus among the native orchids. It consists of 38 species (Tan, 1984), that is, more than 20% of the total number of orchids in Singapore.
The first orchid species that comes to mind always is the pigeon orchid, Dendrobium crumenatum. These orchids can be commonly seen growing on the trunk of road side trees. It is a delight to see them in bloom because the flowers are sweetly scented. The species flower 9 to 10 days after a heavy rain storm. Similar flowering patterns were also observed in some native Bulbophyllum, Thrixspermum, Bromheadia and Taeniophyllum species.
Another interesting, but rare native is Dendrobium leonis, section Aporum. Its leaves are laterally flattened, thick and fleshy, and alternate in two rows. Individual yellowish-green flowers are borne near the apex of the stems. The flowers are only 1.5 cm across, and have an extremely sweet vanilla-like fragrance which can be detected from a distance of 5 m. Two other native species of Dendrobium, which belong to the Section Aporum, are D. aloifolium and D. grande. D. aloifolium bears flowers which are 4 mm in diameter and probably the smallest in the section. D. grande has yellowish-green flowers, about 9 mm wide, tinted with red near the base of the sepals and petals, and the lip is deeply clefted.
Bulbophyllum is the second largest orchid genus in Singapore. Species of this genus are divided into many sections. Of the 28 recorded species (Tan, 1984), Bulbophyllum vaginatum, which belongs to the section Cirrhopetalum is one of the most unusual. They grow in fairly exposed areas. Some of them grow naturally on branches of rain trees and of Eugenia grandis in the Singapore Botanic Gardens. They usually cover an extensive area of a branch, and produce a spectacular sight when in full bloom. The flowers are creamy-yellow. About 15 of them are arranged in a fan shape whorl or in a circle at the tip of the scape. There is another Singapore native, Bulbophyllum medusae, which resembles Bulbophyllum vaginatum, except that the former has paler and longer lateral sepals (12 cm). In the Bukit Timah Nature Reserve, there is a clump of Bulbophyllum membranaceum creeping on a large piece of granite. It is one of the smallest native orchids. Its flowers are very small (of about 6 mm long) and do not completely open. The upper sepal is pale yellow, whereas lateral sepals are dark red, and the petals which are 1.5 mm long, appear translucent. Other interesting Bulbophyllum of Singapore are Bulbophyllum purpurescens, B. lepidum and B. blumei.
Vanilla is one of the most widely distributed orchid genera in the world. It consists of about 100 species distributed throughout the tropics, from Central and South America, across Central Africa, Southern India, Sri Lanka, all of Southeast Asia to the Pacific Islands. In Singapore, the genus is represented by Vanilla griffithii, a relatively common epiphytic climber found in the Upper Pierce Reservoir, Nee Soon and the Mandai Forest. The plant climbs on tree trunks in a zig- zag fashion. Petals and sepals of the flower are white, flushed with pale green, of 2.5 to 3 cm long, and 1.4 to 1.5 cm wide. The lip is white with a pale yellow tip, and is hairy in the middle.
Three species of Cymbidium have been recorded in Singapore, they were Cymbidium bicolor var. pubescens, Cymbidium aloifolium and Cymbidium finlaysonianum. All native Cymbidium species are epiphytes, the most common being Cymbidium finlaysonianum.
Next is the genus Coelogyne. There are 4 species of Coelogyne among our natives, of which Coelogyne pandurata is one of the most outstanding. The flower is about 6.5 cm across. Its petals and sepals have an attractive, clear apple-green colour. The protruding lip has some conspicuous dark brown/red, almost black markings, hence, the name 'Black Orchid' has been given to them.
Let us now turn to the genus Thrixspermum. Most Thrixspermum species are epiphytes. Several species have been recorded in Singapore. They are, Thrixspermum calceolus, T. amplexicaule (or T. lilacinum), T. notabile, T. ridleyanum, and T. trichoglottis. Thrixspermum amplexicaule is the most attractive which is pale lilac in colour, and about 3 cm in diameter. The plant was found in a semi-aquatic habitat in Singapore. Thrixspermum trichoglottis can also be found in nature areas in Singapore. The plants are very small with long seed capsules. The flowers are creamy yellow, with brown spot on the lip.
Although Singapore is a small country, it is the home of Grammatophyllum speciosum, the largest orchid plant in the world. G. speciosum, also known as the Tiger orchid because of the markings on the flowers which resemble the skin of a tiger, is extremely rare if not already extinct in the wild in Singapore. It was last found in Tuas and Pulau Ubin (Ridley, 1900). A mature plant could weigh over a ton. It is a wonder that such a huge plant could live on the trunk of a tree.
Next, let us look at the extraordinary genus Taeniophyllum, the "leafless" orchid. The stems of these plants are greatly reduced and covered by scale like leaves. Roots are fleshy and spread over the bark of its host tree, usually on top of a thin layer of moss. They are green because all replace the leaves as the photosynthetic organ. As the plant is almost flat and its colour blends very well with its host, one can hardly spot them in the wild. T. obtusum can be found near swampy area in Singapore. The roots of the plant were about 2 to 3 mm wide. Flowering is gregarious. The flower is 5 mm wide, its petals and sepals are orange-yellow, and the lip is fleshy and concave, being white in colour. Flowers only last for one day. Some of the Taeniophyllum species are known to give out sweet fragrance to attract pollinators.
Lastly, there are other beautiful native epiphytes, they are Pomatocalpa latifolia, Arachnis hookeriana, Rhynchostylis gigantea, Renanthera histrionica, Phalaenopsis cornu-cervi, Liparis elegans, Liparis hyacinthoides, Eria, javanica, Eria pudica, Eria pulchella, Dipodium pictum, Ariopsis javanica and Flickingeria comata. Some of these are extremely rarely if not extinct in Singapore.
Let us look at the terrestrial orchids.
About 25% of the total number of native orchid species are terrestrials.
The two most common terrestrial species are Spathoglottis plicata and Arundina graminifolia.
Spathoglottis plicata can be frequently seen in open area in the Bukit Timah Nature Reserve and the Central Catchment area. They are usually found among grasses and ferns. There are two varieties of the local species, the dark pink and the alba form. Spathoglottis plicata is very free flowering and has been used for landscapping.
Arundina graminifolia grows in similar habitat as Spathoglottis plicata. The vegetative parts of the plant also resembles bamboo, that is why it is also known as the bamboo orchid. The plant is very free flowering in the lowland tropics.
Some of the native species prefer to grow under semi-shade, they are usually found along road side or hill slopes, familiar examples are Bromheadia finlaysoniana and Eulophia graminea.
Like Dendrobium crumenatum, Bromheadia finlaysoniana flowers a few days after rain. The flower is very attractive, faintly scented, white, with a yellow patch on the lip. Unfortunately, the flower only last for a few hours.
Next is the genus Eulophia. It is represented by 2 species in Singapore, namely, E. graminea and E. squalida. E. graminea can be found among grasses, in partially shaded hill slope and wasteland. They are very hardy plants. E. squalida can be found in the Bukit Timah Nature Reserve, growing on a rather steep slope. Its colour is rather unusual. The sepals are brownish-olive and the petals are white. The lip is pale mauve and has a white central area.
The final group of orchids dwells on forest floor where the light intensity usually does not exceed 3000 lux during most of the day. Occassionally, sunrays manage to penetrate the canopy to reach the forest floor. Nephelaphyllum pulchrum, Calanthe pulchra, Plocoglottis javanica, Cystorchis variegata and Claderia viridiflora fall into this category.
Nephelaphyllum pulchrum has very interesting and showy leaves and delicate flowers. The leaves are fleshy, they are mottled light and dark green and flushed with purple. The flowers tend to crowd together on the short spike. The pinkish sepals and petals are about 1.3cm long, all of them curve downwards.
Calanthe pulchra has striking orange flowers that do not open completely. The flowers are densely crowded along the 50 to 60 cm long inflorescence. A distinguishing feature of the flower is that its spur curves up like a hook. The leaves can reach a length of 70 cm and 10 cm wide.
Plocoglottis javanica is quite a common terrestrial orchid in Singapore. The inconspicuous plant has long pseudobulbs which bear a single leaf. The leaves are 35 cm long by 10 to 12 cm wide. The long flower spike carries some yellow flowers that are spotted with red.
Unlike Plocoglottis javanica, Cystorchis variegata is a very rare species. This is another native species that has very attractive foliage. The leaves are arranged towards the apical part of the rhizome. They are light green in colour with a darker network of venations. The half-opened flowers are borne on the elongated flower spike; the sepals are brown with a tinge of pink while the petals are white.
Claderia viridiflora can also be found on the forest floor of Singapore. The flower spike bears a succession of many flowers, one or two at a time. The flowers are greenish, sepals and petals are about 2.5cm long.
Zeuxine clandestina is one of the less well known orchid found in Singapore. Quite a big population of the species was found in Bukit Timah, growing on the floor of a secondary forest. The plant is an inconspicuous creeper, with fleshy rhizome. A young plant lies rather close to the ground, just like grass. When it begins to bloom, a flower spike of about 10 to 20 cm protrudes from the ground, bearing many small flowers. The flowers are light green in colour and hardly open. The sepals are hairy, and about 3mm long. The lip is a little shorter than the sepals.
Some beautiful Jewel orchids species which were recorded in Singapore include Anoectochilus albolineatus and Macodes petola.
The last group of terrestrial orchids are mycotrophic (Arditti, 1992). These orchids are parasitic on the fungi that associate with them. All orchids rely on mycorrhizae for their early growth, but the mycotrophic orchids depend on the fungus to provide them with nutrients throughout their life. These species usually dwell on forest floor under dense canopy, in area where little light can reach. An examples is Didymoplexis pallens, found in Bukit Timah Nature Reserve. The species has a fleshy underground rhizome, the flower spike is soft and slender, bearing several flowers. The flowers are pale brown olive, with a tinge of pink, it is about 1.4cm long. The dorsal sepal fuses to the petals for half its length; lateral sepals are also joined to the petals towards the base. The lip is light yellow, about 5mm long. The species is not easily seen because it has no visible vegetative part except for the erect flower spike, which can hardly be noticed in its natural habitat. However, if a flower is pollinated, the seed capsule can be seen in the wild. Owing to the difficulties in locating the plant, very little is known about this orchid. Last year, we also discovered another mycotropic orchid, Leucanorchis multiflora, at the Nature Reserve.
Examples of other native terrestrial orchids of Singapore are Corymborkis veratrifolia and Phaius tankervilleae. Several primitive species can also be found like Apostatasia nuda and Neuwiedia veratrifolia.
In 1998, about 221 species of native orchid were recorded in Singapore (Keng et al., 1998). However, based on lists in a preliminary report on the conservation status of plants native to Singapore (Ng and Wee, 1994: Tan, 1995), about 170 orchid species are already considered to be extinct and only 4 are viewed as common. The remaining are placed within the “Endangered”, “Vulnerable” and “Rare” categories or have an indeterminate status. This means that more than 90% of the native orchids in Singapore are either endangered, vulnerable, rare or extinct. A comparison of habitats in the Island 150 years ago with today, shows that most of the mangrove and marshy areas have been replaced by industrial estates or residential areas. Forest and mangrove areas such as those at Choa Chu Kang, Jurong, Ang Mo Kio and Serangoon, where native orchids used to thrive, no longer exist. Therefore an orchid conservation programme was initiated to monitor these species and to attempt to find ways and means to conserve their germplasm and to increase their number for subsequent re-introduction into appropriate habitats in the nature reserves, parks and roadside trees.
First, we need to propagate the species vegetatively and by in vitro culture. To increase the population of some of the rarer species, they will either be selfed or sibbed, seeds are germinated in vitro (Yam and Weatherhead, 1988) and seedlings are introduced back to nature. So far, we have managed to propagate a number of them and have re-introduced three species, Grammatophyllum speciosum, the tiger orchid, Bulbophyllum vaginatum and Bulbophyllum membranaceum, back to the nature area in Singapore.
Mr H. N. Ridley, a Director of the Gardens recorded that the Tiger Orchid was found in the wild in Toas (Tuas) and Pulau Ubin in 1900 (Ridley, 1900). Unfortunately, naturally occuring plants are now extinct.
A few years ago, a Tiger Orchid in the Gardens flowered and was self-pollinated. The huge seedpod was harvested 7 months later. Seeds germinated one month after being sown on Knudson C (Knudson, 1946) medium. After 12 months in the laboratory, the seedlings were planted out in the nursery.
Since the Tiger orchid occurred naturally in Pulau Ubin, the first batch of seedlings was re-introduced there in July 1999 when they were 26 months old and about 15 - 20 cm tall with 5 - 6 leaves. They were affixed on durian, rambutan, mango, Angsana, Tembusu and Rain trees. Seedlings were also planted on trees in the Gardens, around the Visitor Centre at the Bukit Timah Nature Reserve, and in the Orchard Boulevard area in the heat of the city.
With experience from the initial trials, we decided to introduce seedlings to the Bukit Batok Nature Park in the beginning of 2001. This time, the seedlings were more mature, about 30 - 40 cm tall with 16 - 20 leaves. They had at least three shoots, a well-established root system and fleshy pseudobulbs. In February 2001, these larger seedlings were planted on trees along Orchard Boulevard and on the yellow rain trees around the Bandstand in the Gardens. In April 2001, the same was introduced to a site adjacent to a mangrove area in Pulau Ubin, and in early May again to the Bukit Timah Nature Reserve. Some 40 seedlings were also planted on rain trees along Holland Road. In December 2002, some 40 seedlings were planted on trees at the Upper Pierce Reservoir. Recently (early 2004), some 20 plants were planted at various urban parks such as Sembawang Park, Kent Ridge Park and Tiong Bahru Park. Our aim is to use the native orchids to educate the public about our rich natural heritage and our responsibility to conserve them.
The seedlings we planted have been growing for almost two five years in their new homes. We observed that a majority of them are doing well. New shoots have developed and roots are firmly established on tree trunks. Unfortunately, most seedlings planted in the Bukit Timah Nature Reserve were damaged or removed by animals (probably by squirrels and monkeys respectively) (TABLE 1).
Seedling size (cm)
Survival rate (%)
|Bukit Timah Nature Reserve||15-20
|Bukit Batok Nature Park||30-40||90|
We hope that the “Tiger Orchid” will continue to thrive well in their new homes. In the near future, more of this beautiful and majestic species will find its way to more nature areas and parks in Singapore.
In 2003 and 2004, two other native orchids, Bulbophyllum vaginatum and Bulbophllym membranaceum have been successfully propagated and re-introduced.
Seeds of these species were collected from plants growing at their natural habitats. The seeds were sown on Knudson C medium. Seedlings were grown on the media to 2-3cm tall before being transferred to the nursery. Some 10 seedlings were planted on fern barks measuring 7cm long by 5cm wide. There were grown at the nursery for 6 months until new shoots began to develop, they were then re-introduced. Host trees were selected based on the same criteria used for re-introducing the tiger orchid. When a suitable tree is selected, fern barks with established seedlings were secured on the tree trunk by nails.
So far, more than 500 seedlings of B. vaginatum and B. membranaceum have been re-introduced. Over 90% have settled down and growing well in their new homes. We have learnt that these seedlings are best planted in slightly shady area, with at least 50% shade to avoid being scorched. We are very pleased to report that most of these seedlings have produced new shoots and are growing onto the bark of the host tree.
Arditti, J. 1992. Fundamentals of Orchid Biology. Wiley-Interscience, New York.
Keng, H., S. C. Chin and H. T. W. Tan. 1998. The Concise Flora of Singapore. Vol. II: Monocotyledons. Singapore University Press. Singapore.
Knudson, L. 1946. A new nutrient solution for the germination of orchid seed. American Orchid Society Bulletin 15: 214-217.
Ng, P. K. L. and Y. C. Wee. eds. 1994. The Singapore red data book: threatened plants & animals of Singapore. Nature Society (Singapore), Singapore.
Ridley, H.N. 1900. Flora of Singapore. Journal of Straits Branch Royal Asiatic Society. 33: 27-196.
Tan, H. T. W. ed. 1995. A Guide to the Threatened plants of Singapore. Singapore Science Centre, Singapore.
Tan, W.K. 1984. Orchid species of Singapore. In: Proceedings of the Fifth Asean Orchid Congress. pg. 8-12.
Yam, T.W. and M.A. Weatherhead. 1988. Germination and seedling development of some Hong Kong orchids. I. Lindleyana 3: 156-160.