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Taxonomy, biology and ecology of rattan

J. Dransfield

John Dransfield is a Senior Principal
Scientific Officer and head
of palm research at the Herbarium,
Royal Botanic Gardens, Kew,
United Kingdom.

Gaps in taxonomic knowledge and confusion in nomenclature are challenges to rattan research and development.

Rattans are spiny climbing palms which are found in the Old World tropics and subtropics and exploited particularly for their flexible stems. The word "rattan" is derived from the Malay "rotan", the common name for climbing palms. Rattan is collected mainly from wild populations, although considerable efforts have recently been focused on the provision of raw cane from cultivated sources.

Cross-section of rattan stem embraced by leaf sheaths

- W. LIESE

The most important product of rattan palms is the cane, the solid rattan stem stripped of its leaf sheaths. (N.B. Rattans are always solid, unlike bamboo which is usually hollow.) The canes are either used in whole (round) form, for example, in furniture frames, or split, peeled or cored for matting and basketry. The range of indigenous uses of rattan canes is vast, from bridges to baskets, fish traps to furniture and crossbow strings to yam ties. Other plant parts of some species of rattan are also utilized and contribute to the survival strategies of many forest-based communities. Fruits of many species are eaten. The palm heart (growing point of the stem) is often harvested for food and, in the Lao People's Democratic Republic and northeastern Thailand, two species - Calamus tenuis and Calamus siamensis - are intensively cultivated for this purpose. Leaves are used for thatching and the petioles (leaf stalks) and rachises (axes of the leaves) of robust short-stemmed species may even be used as fishing poles. The very spiny leaf rachis of an undescribed species in Bali is used as a food grater, and the whip-like climbing organs of several species have been used to snare flying foxes. Fruits and leaves are sometimes used in traditional medicines. Leaflets of a few species are used as cigarette papers, and leaf sheaths of others as toothbrushes. Many species are ornamental, especially when young, and are sold locally as horticultural subjects. Finally, some species of Daemonorops (e.g. D. draco) provide one source (there are other non-palm sources) of dragon's blood, a red resin that exudes between the fruit scales and is used medicinally and as a dye.

Coconut grater made from the leaf stalks of a Calamus species, Bali, Indonesia

- J. DRANSFIELD

Not all rattans are equally useful, and not all have potential commercial applications. Stem diameter varies greatly from 2 to 3 mm among the smallest species to 10 cm in exceptionally large species. Species of different diameters are used for different purposes. Furthermore, within a size class, not all species are of equal quality; some are inflexible and prone to breakage, others are of poor external appearance. While there may be substantial spontaneous uses for many species (Dransfield and Manokaran, 1994; FAO, 1998; Sunderland, 1998), it is estimated that only 20 percent of the known rattan species are of any commercial value (Dransfield and Manokaran, 1994).

In many areas, the sustainable exploitation and commercial utilization of the rattan resource are hindered by the lack of a sound taxonomic base, which is necessary for meaningful and reproducible research, inventories of the resource, population studies, distinction of commercially valuable species and assessment of silvicultural potential. This article summarizes current knowledge and problems in rattan taxonomy. It also gives a general overview of the biology and ecology of the group and brief information on conservation status and growth rates - areas of research critical to the development of the resource.

All of the species within the Calamoideae - shown here Plectocomiopsis mira, Sarawak - are characterized by overlapping reflexed scales on the fruit

- J. DRANSFIELD

TAXONOMY

Rattans are climbing palms belonging to the Calamoideae, a large subfamily of the palm family (Palmae or Arecaceae). There are around 600 different species of rattan belonging to 13 genera (see Table). These are concentrated solely in the Old World tropics; there are no true rattans in the New World, although climbing representatives of two other palm groups are known in Central and South America. Similarly, there are no rattans in Madagascar. All of the species within the Calamoideae are characterized by overlapping reflexed (bent or curved backwards) scales on the fruit, and all are spiny, a necessary pre-adaptation to the climbing habit (Dransfield, 1992b). (Some species are shrubby palms of the forest undergrowth and do not in fact climb; nevertheless, reproductive features link them with other species that are climbers, and they are hence included in the rattan genera.)

Of the 13 genera of rattan, three (Laccosperma [syn. Ancistrophyllum], Eremospatha and Oncocalamus) are endemic to Africa. Although some species within these genera are utilized locally and form the base of a thriving cottage industry, they have only recently begun to attract attention from commercial concerns (Dransfield, 1992b; Sunderland, 1999; Editor's note: see also article by Sunderland in this issue).

The largest rattan genus is Calamus, with about 370 species. Calamus is predominantly an Asian genus and ranges from the Indian subcontinent and south China southwards and east through Malaysia and Indonesia to Fiji, Vanuatu and tropical and subtropical parts of eastern Australia. It is represented in Africa by one species, C. deërratus, which exhibits high variability among populations. Most of the best commercial species of rattan are members of the genus Calamus. The remaining rattan genera, Daemonorops, Ceratolobus, Korthalsia, Plectocomia, Plectocomiopsis, Myrialepis, Calospatha, Pogonotium and Retispatha, have a range centred in Southeast Asia and extending from there eastwards and northwards (Uhl and Dransfield, 1987; Dransfield, 1992a).

Rattan genera: number of species and their distribution

Genus

Number of species

Distribution

Calamus

~370-400

Tropical Africa, India, Sri Lanka, China, south and east to Fiji, Vanuatu and eastern Australia

Calospatha

1

Endemic to peninsular Malaysia

Ceratolobus

6

Malay Peninsula, Indonesia (Sumatra, Borneo, Java)

Daemonorops

~115

India and China to westernmost New Guinea

Eremospatha

10

Humid tropical Africa

Korthalsia

~26

Indochina to New Guinea

Laccosperma

5

Humid tropical Africa

Myrialepis

1

Indochina, Thailand, Myanmar, peninsular Malaysia and Sumatra

Oncocalamus

4

Humid tropical Africa

Plectocomia Philippines

~16

Himalayas and south China to peninsular Malaysia, Singapore, Sumatra, Java, Borneo and the

Plectocomiopsis

~5

Lao People's Democratic Republic, Thailand, peninsular Malaysia, Borneo, Sumatra

Pogonotium

3

Two species endemic to Borneo, one species in both peninsular Malaysia and Borneo

Retispatha

1

Endemic to Borneo

Source: Modified from Uhl and Dransfield, 1987.

Despite the commercial importance of rattan, basic knowledge of the resource is somewhat limited and the rattan flora of Africa and much of Southeast Asia remains poorly known. Since most taxonomic studies have been country-based, there is a tendency for unidentified species to be described as new local endemics when they may well be species described and well known in neighbouring areas. Such problems occur particularly where species distributions cross political boundaries, for example in Indochina.

In addition, a rather narrow species concept has led to a proliferation of new names. Resolving some of the taxonomic and nomenclatural problems related to this has been difficult, given language barriers and the difficulty of exchanging material. In China, in particular, several taxa widespread in Asia have been described as new Chinese species or varieties. Painstaking work has been needed to resolve the major taxonomic problems of Indochinese rattans (Evans et al., 2001).

Similarly, in Africa, three large rattans with different ecology and different cane quality were at some time all referred to in different countries as Laccosperma secundiflorum. A regional approach was needed to sort out this basic taxonomy.

A material difficult to substitute

In the absence of rattans, local communities throughout the tropics use a variety of plant resources for the purposes for which rattan is used - basketry, matting, binding, etc. However rattan, if available, is preferred, and few products other than true rattan have the strength and flexibility to be utilized for furniture production. Bamboo, raffia (Raphia spp.), willow (Salix spp.) and buri palm (Corypha utan) are used locally for some sorts of furniture, but in the international market these products do not command prices comparable to those of rattan furniture. Of the other genera of climbing palms, only Desmoncus spp. furnish stems of sufficiently good quality to be used as rattan substitutes. While rattan substitutes may be locally significant and socially important, there is no doubt that rattan is pre-eminent.

Taxonomic work of this kind is not purely an academic exercise; it is an essential basis for the development of the rattan resource and underpins the conservation and sustainable development objectives that are much advocated for rattans. Species delimitation must be clearly understood; it is essential to know which species are of commercial importance and how they may be distinguished from other species. This knowledge is critical for meaningful inventories of commercially important taxa and assessment of the silvicultural potential of each species, based on sound ecological knowledge. Reference to a structured systematic framework also ensures that any experimental work undertaken is replicable.

Local classification

The development of extensive indigenous classification systems for rattans often reflects the social significance of rattan, and these taxonomies have developed to reflect rattan as it grows in the forest, as well as how it is used. For example, a widespread species may be referred to by many names because its range encompasses a number of language groups. Often, one species can be given many names, reflecting the different uses of the plant or the various stages of development from juvenile to adult. Commonly, blanket names for "cane" are given to a wide range of species.

Some species that have no use are often classified according to their "relationship" to those that are utilized. These are often along kinship lines, and species may be referred to as "uncle of..." or "small brother of..." reflecting their perceived relationship with and similarity to species that are widely utilized. In the past, the uncritical use of vernacular names has created serious confusion and contributed to the misconception that all species are of commercial potential. This confusion could be avoided if the literature on rattan would refer always to the species by their Latin names. Glossaries that link local and Latin names have often been used uncritically, resulting in confusion and unverifiable research results. Citations of species names that are linked to actual herbarium specimens allow verification and reproducible research.

BIOLOGY AND ECOLOGY

The range of rattans extends from sea level to more than 3 000 m elevation, from equatorial rain forests to monsoon savannahs and the foothills of the Himalayas. Thus the large number of rattan species is matched by great ecological adaptation and diversity. Most, admittedly crude, ecological preferences for rattan species have generally been identified during taxonomic inventory work, yet these broad ecological summaries are invaluable as a basis for establishing cultivation procedures.

A major gap in the knowledge of rattans, even of the commercial species, is an understanding of population dynamics and demography. Information on the population structure, distribution, rate of regeneration and the number of harvestable stems per hectare of each species is essential to a solid understanding of potential sustainability.

Forest type and light requirements

Throughout their natural range, rattan species are found in a wide variety of forest and soil types. Some species are common components of the forest understorey. Others rely on good light penetration for their development; hence some species are found in gap vegetation and may respond well to canopy manipulation. Some species grow in swamps and seasonally inundated forest, while others are more common on dry ridge tops.

Cultivation trials on many of the Southeast Asian species, as well as recent germination trials of the African taxa, have indicated that seeds will germinate under a wide range of light conditions. The resultant seedlings will remain for long periods on the forest floor until the light becomes sufficient for them to develop, as could happen for example through tree fall. This seedling bank is a common feature of the regeneration of most species and is a well-recognized component of forests where rattans occur.

Life form

Rattans can be clustering (clump-forming) or solitary; some species, such as Calamus subinermis, can be both. Other species have short or subterranean stems. Clustering species sometimes possess more than 50 stems of varying ages in each clump and produce suckers that continually replace stems lost through natural mortality or harvesting. Some clumps can be harvested many times on a defined cycle if the light conditions are conducive to the remaining suckers being able to develop and elongate. Ensuring that stem removal through harvesting does not exceed stem replacement is the crux of rattan sustainability.

An even more crucial component of sustainability is the monitoring of the exploitation of solitary species. Calamus manan, one of the most commonly exploited rattan species, is single-stemmed; thus the impacts of harvesting this species are much greater than those of harvesting clustering rattans. Sustainability of such species relies on recruitment through sexual rather than vegetative means.

Flowering

Another ecological feature of palms that is important in terms of management is that rattans display two main modes of flowering: hapaxanthy (flowering once) and pleonanthy (multiple flowering). Hapaxanthy is characterized by simultaneous production of flowers after a period of vegetative growth. Flowering and fruiting is followed by the death of the stem itself. In single-stemmed hapaxanthic rattan species, the whole organism dies after the reproductive event. However, in clustering species the organism continues to regenerate from the base, and it is only the individual stem that dies.

In pleonanthic species, flowers are produced continually and flowering and fruiting do not result in the death of the stem.

All the species of Korthalsia, Laccosperma, Plectocomia, Plectocom-iopsis and Myrialepis, and a few species of Daemonorops are hapaxanthic. All other rattan species are pleonanthic.

In terms of silviculture, the mode of flowering affects the cutting regime and stem selection for harvest, particularly if the cultivated resource is to supply seed for further trials. Furthermore, in many hapaxanthic species, stems tend to be of low quality because they have a soft pith which results in poor bending properties. These stems are also more prone to subsequent insect attack because of increased starch deposition.

The leaf sheath of Daemonorops sabut has interlocking combs of spines that provide galleries for nesting ants

- J. DRANSFIELD

Fruits and seeds

Rattan fruits are often brightly coloured (yellow, orange or red) and the outer seed coat (sarcotesta) is also attractive to birds and mammals. Hornbills and primates are the main dispersers of rattan seeds in both Southeast Asia and Africa, with primates and elephants also sharing a preference for the ripe fruit. Fruits are often ingested whole and pass through the intestinal tract with the seed intact, or are sucked and spat out.

In the Asian taxa, the seed is usually covered with a sarcotesta. Incomplete removal of the sarcotesta often results in delayed germination, which suggests that it contains some chemical germination inhibitors. Once this outer layer is fully removed, the germination of commercial species such as C. manan and Calamus caesius is both rapid and uniform. In contrast, commercially important species in Africa have a relatively robust seed coat which acts as a barrier to imbibition, causing a dormancy that can last from 9 to 12 months before germination commences. This physical dormancy has caused some difficulties in the cultivation of some species, and research has been undertaken to reduce the germination times. Soaking the seeds in water for at least 24 hours prior to sowing is probably the most effective means of inducing early germination (Sunderland and Nkefor, 2000).

Several attempts have been made to develop methods for long-term storage of rattan seed. Pritchard and Davies (1999) demonstrated the possibility of short-term hydrated storage of rattan seed for periods of up to six months.

Rattan and ant relationships

Several species of rattan (e.g. some species of Laccosperma, Eremospatha, Korthalsia, Calamus and Daemonorops) have developed morphological adaptations that provide nesting sites for ants, such as hollowed out acanthophylls (thorn-like organs), interlocking spines that form galleries, curved back leaflets that tightly clasp the stem, or inflated leaf sheath extensions. This relationship is complex and has yet to be fully investigated. One part of the relationship, for example, is the "farming" of scale insects by the ants. The scale insects feed on the rattan phloem cells, secreting a sweet honeydew that the ants then feed on. The ants, in turn, may protect the rattan from other predators (unfortunately including rattan harvesters and unwitting botanists); however, this complex relationship requires further study.

CONSERVATION OF THE RESOURCE

Threats to rattan come from several sources including:

Of the approximately 600 species of rattan, the World Conservation Union (IUCN) Red List records 117 taxa as threatened to some degree; of these, 21 are endangered, 38 are regarded as vulnerable, 28 as rare, and 30 as indeterminate (Walter and Gillett, 1998). However, while this listing may give some indication of the global threats to rattan species, the conservation status is known with precision for only very few of the listed species. Species are assigned to these categories based on crude estimates of distribution and threat rather than on detailed studies. A little is known about the precise distribution and conservation status of a very few species, such as Ceratolobus glaucescens, which are restricted to certain geographic areas and soils. At the other end of the scale are species such as Calamus poilanei, which have a wide natural range but for which the remaining population and the degree of threat cannot be estimated based on factors such as remaining forest cover and distribution of soils because they are overexploited throughout their range. Monitoring of the amount of cane emerging from the forest and on-the-ground surveys in the forest can only suggest that the population is severely overexploited.

Efforts to conserve valuable rattan resources by introducing sustainable management systems have not proved very successful, and conservation of the resource in reserves where rattan harvesting is strictly forbidden requires control and policing which have proved virtually impossible in all reserves in Southeast Asia. There is therefore a serious need to focus additional effort on rattan conservation.

CONCLUSIONS

Existing information on the natural history and ecology of rattans (summarized in Wan Razali, Dransfield and Manokaran, 1992; Dransfield and Manokaran, 1994) is sufficient as a basis for developing rattan plantings of the best quality species such as C. manan and C. caesius. There remain major gaps in the knowledge of the taxonomy of rattans, particularly in Myanmar, the Indonesian islands of Sulawesi and Maluku, and New Guinea. There are also major gaps in the understanding of rattan demography, information essential to the development of sustainable harvesting strategies. 

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