52

9: Plants yielding non-seed carbohydrates

Arenga Labill.

DC., Bull. Sc. Soc. Phil. 2: 162 (1800).

PALMAE

x = 16

Major species and synonyms
-Arenga microcarpa Beccari, in Schum. & Hollr., Fl. Kaiser Wilhelmsland: 16 (1889), synonyms: Arenga gracilicaulis Bailey (1898), Didymosperma humile (non Reinw. ex Kunth) Schum. & Lauterb. (1901), Didymosper microcarpum (Beccari) Warb. ex Schum. & Lauterb. (1901).
-Arenga obtusifolia Martius, Hist. nat. palm. 3: 191 (1838), synonym: Saguerus langkap Blume (1843).
-Arenga pinnata (Wurmb) Merrill -see separate article.
-Arenga tremula (Blanco) Beccari, Philip. Journ. Sci. 4: 612 (1909), synonyms: Caryota tremula Blanco (1827), Wallichia tremula (Blanco) Kunth (1841), Didymosperma tremula (Blanco) H.A. Wendl. & Drude (1878).
-Arenga undulatifolia Beccari, Malesia 3: 92 (1889), synonym: Arenga ambong Beccari (1907).
-Arenga westerhoutii Griffith, Calc. J. Nat. Hist. 5: 474 (1845).

General: Arenga, sugar palm (En). Arenga, palmier à sucre (Fr). Sugar palm is particularly applied to Arenga pinnata and Arenga westerhoutii.
- Arenga microcarpa. Indonesia: aren sagu (Indonesian), sagu baruk (Talaud Islands), pepe tinggi (Halmahera). Papua New Guinea: wana kuk (Jal, Madang), wokabim (Bogia, Madang), iri (Pogatumo, Sumo).
- Arenga obtusifolia. Indonesia: langkap (Indonesian), bolangan (Sumatra), langko (Sumatra). Malaysia: rangkap, pangkap. Thailand: langkap (southern).
- Arenga tremula. Philippines: dumyaka (Tagalog), abigi (Bikol), baris (Bagobo).
- Arenga undulatifolia. Indonesia: aren gelora (Indonesian), aping (Dayak), ake (Central Sulawesi). Malaysia: bangkala (Kedayan, Sabah), toki (Bajau, Sabah), aping (Iban, Sarawak). Philippines: ambong (Sulu), bat-bat (Tagbanua), caong (Luzon).
- Arenga westerhoutii. Malaysia: langkap (Penang), anowe kutare (Malaka), gtor (Perak). Thailand: langkap (Yala, Pattani), rangkap (southern), rangkai (central).

Arenga comprises 22 species ranging from India, southern China, Ryukyu Islands and Taiwan, throughout South- East Asia and Christmas Island to northern Australia, with the greatest diversity on the Sunda Shelf.
- Arenga microcarpa is native to Indonesia (from Sangihe and the Talaud islands through the Moluccas to Irian Jaya) and Papua New Guinea. It is sometimes cultivated in this area (e.g. in Sangihe and Talaud Islands).
- Arenga obtusifolia occurs in Thailand, Cambodia, Peninsular Malaysia, Sumatra and Java.
- Arenga tremula is found in the Philippines, Hainan, Taiwan and the Ryukyu Islands.
- Arenga undulatifolia occurs in Indonesia (Kalimantan, Sulawesi), Malaysia (Sarawak, Sabah) and the Philippines.
- Arenga westerhoutii is native to Peninsular Malaysia, Vietnam and Thailand.

The taller Arenga palms store large quantities of starch in their stem that are later converted into sugar to be translocated to the inflorescences. The sugar can be drawn off in the juice by tapping the peduncle and rachis of the male inflorescence. By far the most important sugar producer in the genus is Arenga pinnata, but other species are used similarly. The starch of the stem can also be harvested. For instance, in Sangihe and the Talaud Islands Arenga microcarpa is cultivated for its starch production from which, for example, cookies known as 'bagea' in North Sulawesi are baked; in Hainan, starch is extracted from Arenga tremula.
The cabbage (young tops) of all species is edible and used as a vegetable, although consuming large quantities e.g. of Arenga tremula can provoke toxic effects. The leaves are used for thatching and wickerwork. The petioles and midribs are used to make baskets (Arenga tremula in the Philippines), arrows for blowpipes (Arenga undulatifolia) and plugs for blowpipe darts are made from the pith of the petiole of Arenga undulatifolia in the Philippines.
Fruits of most species are poisonous and are sometimes used medicinally and criminally. The wood of some species is used to make small utensils or is even used in construction, but it is said not to be durable (e.g. Arenga obtusifolia, Arenga westerhoutii). All species have recognized or potential ornamental value.

Of the Arenga sugar palms, only products of Arenga pinnata are traded beyond the local market. Few statistics are available. In the Talaud Islands, about 30 000 t of starch is produced annually from 20 000 ha of Arenga microcarpa planted in village gardens.
Trade in seed and seedlings of Arenga for ornamental planting is still very limited.

Hardly any data are available on the nutritional composition of the edible parts, nor on the specific of the carbohydrates.
The fleshy mesocarp of the fruits usually contains many oxalate crystals, making the flesh inedible.

Dwarf to large, solitary or clustered, usually unarmed, usually hapaxanthic, sometimes pleonanthic, monoecious, shrubby, stemless or tree palms. Stem with distinct internodes, usually obscured by persistent fibrous leaf bases and sheaths. Leaves flabellate, usually induplicate and imparipinnate; sheath covered with hairs or scales, often extending into a ligule, eventually disintegrating into a mass of black fibres; petiole usually well developed, slender to robust, channeled or ridged, hairy; leaflets singlefold, arranged or grouped regularly and held in several planes, or deeply lobed and wavy, distal margins jaggedly toothed with small sharp teeth, variously tomentose to glabrescent. Inflorescences usually interfoliar and produced in a basipetal sequence (hapaxanthic type) or in acropetal sequence (pleonanthic type), usually solitary and branched to 1-2 orders, usually unisexual with pistillate inflorescences tending to be distal to the staminate ones and sometimes much larger; peduncle very short to well developed, slender to massive, with conspicuous bracts; rachillas erect or pendulous, distant or crowded, slender to massive, bearing a loose to dense spiral of triads; flowers in triads, sessile, consisting of one female between two males, but by abortion of one sex the inflorescences usually unisexual; male flower ellipsoidal, sepals and petals 3, coriaceous to fleshy, stamens (6-)20- 90(-300); female flower globose, sepals and petals 3, coriaceous to fleshy, ovary trilocular, stigmas 2-3. Fruit a globose to ellipsoidal drupe, often triangular in cross-section, exocarp smooth and variously coloured, mesocarp fleshy with numerous raphides, endocarp not differentiated. Seed 1-3, usually ellipsoidal, hard, with homogeneous endosperm, lateral embryo and remote-tubular germination.
- Arenga microcarpa. Medium-sized hapaxanthic tree, growing in clusters. Stem 4-8(-14) m tall, internodes 20 cm long, 12 cm in diameter. Leaves on the stem 5-10; sheath 50-80(-130) cm long, near margin rather fibrous; ligule 40 cm long; petiole 25-40(-100) cm long, about 2 cm in diameter, surface rough; blade in outline 4-6 m x 1.4 m with 40-60(- 70) leaflets on either side; there are 8 upright leaflets on either side of the base of the blade; leaflets in groups of 2-4, linear, 40-110 cm x 2-5 cm, flat, margin sparsely praemorse. Male inflorescence single or multiple, 60 cm x 30 cm; peduncle about 10-15 cm x 2.5 cm; rachillas 30, slender, 45-80 cm long. Female inflorescence always single, size similar to the male one. Fruit globose, about 1.5 cm in diameter, bright red.
- Arenga obtusifolia. Pleonanthic tree, growing in clusters. Stem up to 20 m tall, internodes 10-15 cm long, 15-30 cm in diameter, stoloniferous; stolons up to 15 m long, 2 cm in diameter. Leaves on the stem about 8; sheath 20 cm long, near margin slightly fibrous; ligule 40 cm long; petiole 40 cm long, 4-6 cm in diameter, surface rough; blade in outline 3-4 m x 2.2 m with about 90 leaflets on each side; leaflets linear, 80-110 cm x 3-4 cm, flat, margin sparsely praemorse. Male inflorescence single, 60 cm x 40 cm; peduncle 20 cm x 5 cm; rachillas 40, slender, 40 cm long. Female inflorescence similar to the male one. Fruit globose to ovoid, 5 cm x 3.5 cm, dark red.
- Arenga tremula. Hapaxanthic shrub, growing in clusters. Stems up to 4 m tall, internodes 15-20 cm long, 8-12 cm in diameter. Leaves on the stem about 6; sheath up to 40 cm long, rather fibrous near margin; ligule tubular, about 15 cm long; petiole 80 cm long, 0.8 cm in diameter, surface rather rough; blade 2 m x 1.2 m with up to about 60 leaflets on each side; leaflets not grouped or in groups of 2-5, linear, 60-100 cm x 2-3.5 cm, upright, flat, margin sparsely praemorse. Male inflorescence single or multiple, 40-60 cm x 30 cm; peduncle 20 cm x 3 cm; rachillas 50, slender, 20-50 cm long. Female inflorescence similar to the male one. Fruit globose, 1-2 cm in diameter, bright red.
- Arenga undulatifolia. Medium-sized hapaxanthic tree, growing in clusters. Stem 4-8 m tall, internodes 15 cm long, 20 cm in diameter. Leaves on the stem about 10; sheath up to 50 cm long, not fibrous; ligule about 40 cm long, rather thorny; petiole 200 cm long, 8 cm in diameter, surface rather rough; blade 5 m x 1 m, with 30-50 leaflets on each side; leaflets linear, 60-120 cm x 6-20 cm, undulate, along margin with many distinct lobes. Inflorescence single or multiple, when multiple usually one large female between various smaller males; male inflorescence 40- 60 cm x 20-40 cm, peduncle about 20 cm x 4 cm, rachillas 5-10, slender, 60-120 cm long; female inflorescence similar to the male ones. Fruit globose, 3-4 cm long, 2.5-3 cm in diameter, dull red.
- Arenga westerhoutii. Hapaxanthic tree, not growing in clusters. Stem 12 m tall, internodes 20-40 cm long, 40 cm in diameter. Leaves on the stem 6-12; sheath 50-150 cm long, fibrous; ligule 40 cm long, fibrous; petiole 100-190 cm long, 9 cm in diameter, surface rough; blade 5.9-6.8 m x 3.1 m with about 100 leaflets on each side, arranged in one plane; leaflets linear, 130 cm x 9.5 cm, flat, margin praemorse. Male inflorescence single, 90-200 cm x 80 cm; peduncle 50 cm x 10 cm; rachillas 60-70, slender, 60 cm long. Female inflorescence similar to the male one. Fruit globose, 4-4.5 cm in diameter, blackish green.

In a humid environment (in litter or about 2 cm underground) seed may start to germinate. In 2-3 months time, a narrow tubular cotyledonary sheath, 2-5 cm long, bearing an embryo, develops laterally from the seed and grows down vertically into the ground. The size of the cotyledon depends on the species, shrubs having a short and small one, tree species a larger one. Later on, a radicle arises from the terminal part of the cotyledon and grows down vertically, followed by 4- 10 adventitious roots which arise radially around the radicle. From the base of the radicle a plumule grows up to the soil surface and the first obovate seedling leaves may appear aboveground after 3-6 months. The stem never branches. Inflorescences arise from every node on the stem of mature plants. Of the 22 species in Arenga, in 17 species (including four of the five described here) growth of the stem is terminated by the reproductive phase, flowering taking place from the top downwards, after which the tree dies (hapaxanthic type); in 5 species (including Arenga obtusifolia described here) flowering starts at the base of the mature stem, proceeding upwards continuously, not followed by the death of the tree (pleonanthic type).

Of the 22 described species in the genus Arenga, 10 species and one subspecies are endemics. The endemics are usually shrubs, consisting of small and rare populations.
In Arenga tremula 2 subspecies are distinguished:
- subsp. tremula: leaf blade with about 60 upright leaflets on each side, the leaflets in groups of 2-5; male inflorescence single or multiple; petals of male flower ellipsoid, 8-10 mm x 6 mm; anthers 3-4 mm long. Occurring in the Philippines.
- subsp. longistamina Mogea: leaf blade with about 28 leaflets on either side which are arranged in one plane and not in groups; male inflorescence always single; petals of male flower oblongoid, 9-12 mm x 5 mm; anthers 6-7 mm long. Occurring in Hainan, Taiwan and the Ryukyu Islands.

Arenga palms are found mainly in primary per-humid tropical forest, rarely in secondary forest, from sea-level up to 1700 m altitude. Arenga microcarpa and Arenga obtusifolia occur up to 700 m altitude, Arenga tremula is restricted to the lowlands, Arenga undulatifolia occurs up to 1500 m and Arenga westerhoutii up to 1400 m altitude.

Hardly any specific information on agronomic aspects is available for the Arenga species considered here. Most probably, these practices will be similar to those for Arenga pinnata. On the Talaud Islands, an annual production of starch of 1.5 t/ha has been reported for Arenga microcarpa from village gardens.

There are no Arenga germplasm collections or breeding programmes. In Indonesia, a living collection of 11 Arenga species is available in the Bogor Botanical Gardens.

Because most Arenga species are useful for sugar, starch and thatch production, and potentially have ornamental value, they deserve much more scientific attention. Germplasm collection is needed urgently as many species have become very rare.

Mogea, J.P., (in press). Revision of the genus Arenga. Reinwardtia 11.
Sihombing, D.A. et al., 1980. Case study sagu baruk di pulau Sangihe Besar, Kabupaten Sangihe Talaud [Case study on 'sagu baruk' in Great Sangihe Island, Sangihe Talaud district]. Inspeksi Dinas Pertanian Rakyat Manado, Manado, Sulawesi, Indonesia. Mimeographed. 41 pp.
Tomlinson, P.B., 1960. Seedling leaves in palms and their morphological significance. Journal of the Arnold Arboretum 41: 414- 428.
Uhl, N.W. & Dransfield, J., 1987. Genera palmarum. The L.H. Bailey Hortorium and The International Palm Society. Allen Press, Lawrence, Kansas, United States. pp. 312-314.

J.P. Mogea & J.S. Siemonsma

Mogea, J.P. & Siemonsma, J.S., 1996. Arenga Labill.. In: Flach, M. & Rumawas, F. (Editors): Plant Resources of South-East Asia No 9: Plants yielding non-seed carbohydrates. PROSEA Foundation, Bogor, Indonesia. Database record: prota4u.org/prosea