Atuna (PROSEA)
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Introduction |
Atuna Raf.
- Protologue: Sylva tellur.: 153 (1838).
- Family: Chrysobalanaceae
- Chromosome number: x= unknown; 2n= unknown
Vernacular names
- Merbatu (trade name).
Origin and geographic distribution
Atuna comprises 8 species which occur in southern India, Thailand and throughout the Malesian region (except for the Lesser Sunda Islands) towards Fiji and Samoa. In Malesia 5 species occur. The genus is very rare in Java and Sulawesi.
Uses
The wood of Atuna is used for house building (beams and rafters), posts and poles (temporary), and especially for salt-water piling and other marine constructions. It is also suitable for parquet flooring and railway sleepers. It provides good fuelwood and good-quality charcoal.
In Ambon a dish called "koku koku" is prepared from the mashed seeds of A. racemosa subsp. excelsa mixed with fish, ginger, onions, chillies and lime juice. In the Solomon Islands pounded seeds of the same species are used to caulk boats and to waterproof bottles made from gourds; the uses of the oil extracted from the seeds include to scent coconut oil and for hairdressing. The bark and pounded seeds are used medicinally against diarrhoea. In Fiji the leaves are used to thatch the outside walls of houses.
Production and international trade
Atuna wood is most likely traded in mixed consignments of medium-weight hardwood or together with that of the genera Maranthes and Parinari as "merbatu". Supplies are, however, limited.
Properties
Atuna yields a medium-weight to heavy hardwood with a density of 685-1000 kg/m3 at 15% moisture content. Heartwood pale brown to red-brown, not clearly demarcated from the paler to white sapwood; grain straight, occasionally interlocked; texture rather fine; wood sometimes fairly indistinctly streaked. Growth rings indistinct, occasionally locally marked by darker zones containing reduced amounts of vessels and parenchyma; vessels medium-sized to very large, almost exclusively solitary; parenchyma abundant, banded in narrow bands; rays fine, visible with a hand lens; ripple marks absent.
The wood seasons with little degrade. It is hard and fairly strong and is very difficult to cut and saw due to its high silica content, but can easily be split for firewood. It is non-durable in contact with the ground or when exposed to the weather, is not resistant to termites, but is fairly resistant to marine borer attack in salt-water. The sapwood is non-susceptible to Lyctus.
See also the table on microscopic wood anatomy.
Botany
- Small to large trees up to 45 m tall; bole up to 100 cm in diameter, fluted at base or with short buttresses; bark surface smooth, often lenticellate, becoming cracked or patchy, with adherent scales, grey, grey-green or black, often with white mottles, inner bark fibrous, hard and gritty, orange-brown or red-brown to purplish, without exudate.
- Leaves alternate, simple, entire, almost glabrous, the veins usually papillose below; stipules keeled, caducous.
- Inflorescence an axillary raceme or contracted panicle.
- Flowers bisexual, zygomorphic, with an obconical to cylindrical receptacle and 5 unequal sepals; petals 5, white; stamens 10-20, filaments free and inserted unilaterally on the margin of the disk; ovary inserted at or near the top of the receptacle, 2-locular with a single ovule in each cell, style 1, emerging from the base of the ovary.
- Fruit a fairly large, hard drupe, crustaceously warty, splitting irregularly to reveal the fibrous interior; cotyledons strongly ruminate.
- Seedling with hypogeal germination; cotyledons not emergent; hypocotyl not developed; all leaves alternate.
The ultimate shoots show a complicated system of divaricate branching. The fruits are dispersed by ocean currents, by a scatter-hoarding squirrel and possibly by wild pigs. A. racemosa subsp. racemosa has been observed to flower in January in Java and to fruit in February in Sumatra.
The family Chrysobalanaceae has sometimes been treated as a subfamily of the Rosaceae. Atuna is closely related to the pantropical genus Parinari. A. racemosa has been divided into 2 subspecies: subsp. racemosa is found throughout the range of the species except for Java, whereas subsp. excelsa (Jack) Prance occurs in Peninsular Malaysia, Sumatra, Java, Borneo, and North Sulawesi.
Ecology
Atuna is found as an understorey or canopy tree in well-drained evergreen lowland and hill forest, often in mixed dipterocarp forest, up to 800 m altitude. A. racemosa subsp. racemosa is also found along rivers, in freshwater or brackish swamps and even in mangrove forest. A. cordata is locally common in hill forest on ultrabasic rock up to 1200 m altitude.
Silviculture
Atuna can be propagated by seed. About 280 dry fruits/kg have been counted for A. racemosa subsp. racemosa.
Genetic resources and breeding
There are no records of conservation of Atuna species, except for a few specimens in botanical gardens. Deforestation may easily endanger those species with a narrow geographical distribution.
Prospects
As Atuna timber is resistant to marine borers, especially when pressure-treated with appropriate preservatives, it will probably continue to be used for marine constructions.
Literature
162, 163, 198, 261, 267, 341, 405, 431, 436, 615, 621, 632, 829, 861, 903, 904, 934, 974, 1048, 1221.
