The true sago palm (Metroxylon sagu Rottboell) is a tree with a trunk or bole which stores large quantities of starch, used by the plant as food for flowering and fruiting. Sago starch is a staple food for Southeast Asia, and the palm grown in all areas of the developing world. Historic period trade routes spread the sago from its origins in New Guinea or the Moluccas from the south Pacific islands westward to Melanesia and Indonesia, Mayasia and Thailand. Today, the sago palm is also grown commercially in plantations, and it has been described (Karim et al) as an underutilized food palm with the potential for much more human use.
Based on the presence of clusters of sago plants around Kelabit settlements in the highlands of Sarawak Island, Borneo, archaeologists suggest that sago may have been cultivated at least as long ago as 1700-1500 cal BP.
New Dates for Sago
A study published in 2013 (Yang et al.) on archaeological investigations at the site of Xincun on the southern coast of China suggests that sago use and cultivation likely occurred in the Neolithic period by at least 4,500 years ago. Xincun is a settlement located on top of a coastal sand dune, near a freshwater lagoon. AMS dates indicate a date between 3500 and 2470 BC. Starch grains and phytoliths identified as coming from a variety of palms, including sago, were recovered from a dozen pestles, grinders and pounders recovered from Xincun. Based on the amount of material recovered from Xincun, Yang et al. suggest that the sago-eaters may have managed sago plants near their settlements.
If the scholars are correct, that pushes the date of domestication for sago to approximately 5,000 years ago. The notion that sago may have predated rice agriculture in tropical areas is not new to Yang et al., (see Barker and Richards), but it is the first evidence supporting the long-term use of sago palm starch.
Metroxylon's Characteristics
Botanists recognize between five and nine species of the sago palm; local growers in Papua New Guinea recognize between 5 and 15. M. sagu is a pinnate-leaved palm which is native to the hot humid tropics of southeast Asia and Oceania. The adult palms have a spiny trunk or bole with diameters averaging between 35-60 centimeters (14-24 inches), and the tree to heights between 6 and 16 meters (20-52 feet). Healthy palms have approximately 24 leaves; the more leaves the palm carries, the larger the trunk diameter. Each frond grows to 5-8 m (16-26 ft) long, with 100-200 leaflets, some of which grow to 150 cm (59 in) long and up to 10 cm (4 in) wide.
Many palm varieties store starch in their trunk, but the sago palm can accumulate up to several hundred kilograms, and survives being repeatedly harvested. The bark is extremely hard, but the pith, once it's been cracked open, is easier to grate than any other starch crop such as cassava. The flour can be stored dried or wet, and it can keep for as long as a month.
Propagation and Extraction
During its life, the sago palm produces suckers, which develop into other boles, so that as an adult, the plant consists of several starch-producing boles. At the end of its life, approximately 5-15 years later, the plant produces a large amount of fruits, and the main bole decays, allowing one of the other boles to continue.
When the palms are considered to be fell-ripe at about 10 years of age, the trunk of the tree is cracked open with an axe. The bole is removed, and typically the top with the leaves attached is left behind. The bole is split into two halves, and the pith removed using an adze or bushknife. The removed pith is repeatedly mixed with water and the starch allowed to stream away, leaving the fibrous material behind. Starch is caught in a vessel and the excess water runs out until the starch settles on the bottom of the vessel. Coppiced and managed, sago palms can be harvested for many years before the palm dies.
Uses for the Sago Palm
The most common food use for the sago palm is pouring hot water over the flour and eating the gluey mass with a spoon. The starch is sometimes rolled in a basket of sago leaves and placed in hot ashes; or baked in ceramic pots or made into cookies or mixed with fish and vegetables. Sago pearls are small particles of wet starch which are heated in a pan until the exteriors are gelatinized, and then cooked in coconut milk and topped off with sugar. Finally, as with other palms, the palm heart itself is often used as a vegetable.
Other uses of the sago palm include using the leaves for thatching or mats, the rachis for horizontal posts in buildings, the trunk cortex for use in fuel for cooking, and the processed pith for use as animal feed and fertilizer. Commercial uses for the starch include human (bread) and animal food, in making paper and textiles, as a biodegradable filler in plastics, and for the production of ethanol. Starch derivatives are used in the paper industry, adhesives, and medicines.
Habitat and Cultivation
Throughout SE Asia there are vast wild stands of M. sagu, estimated in 2009 at 2 million hectares, and about 14,000 hectares of cultivated sago. Semi-cultivated stands are those which have been planted from suckers near villages, and then tended by cleaning and pruning. Yields on semi-cultivated stands range between 150-400 kg of dry starch. Roughly 150-160 hours of work are needed to produce enough starch for one person for a full year, working out to about 6,000 kcal/hour/person. Cultivar changes are minor, although some no longer produce suckers, and must be replanted when they die.
The best habitat for the swamp sago is the moderately wet, seasonally flooded parts of a swamp: too wet and the sago won't grow. In wild stands, sago plants dominate but compete with one another for space. The drier the land, the more starch is produced in a sago; but in these locations they compete with dicoytledonous trees for available light.
Sources
This glossary entry is a part of the About.com guide to the Plant Domestication, and the Dictionary of Archaeology.
Barker G, and Richards MB. 2013. Foraging-Farming Transitions in Island Southeast Asia. Journal of Archaeological Method and Theory 20(2):256-280.
Barton H. 2012. The reversed fortunes of sago and rice, Oryza sativa, in the rainforests of Sarawak, Borneo. Quaternary International 249(0):96-104.
Ellen RF. 2006. Local knowledge and management of sago palm (Metroxylon sagu Rottboell) diversity in south central Seram, Maluku, Eastern Indonesia. Journal of Ethnobiology 26(2):258-298.
Flach M. 1997. The sago palm. Metroxylon sagu Rottb. Rome, Italy: International Plant Genetic Resources Institute.
Karim AA, Pei-Lang Tie A, Manan DMA, and Zaidul ISM. 2009. Starch from the Sago (Metroxylon sagu) Palm Tree--properties, prospects, and challenges as a new industrial source for food and other uses. Comprehensive Reviews in Food Science and Food Safety 7:215-228.
Kjær A, Barfod AS, Asmussen CB, and Seberg O. 2004. Investigation of Genetic and Morphological Variation in the Sago Palm (Metroxylon sagu; Arecaceae) in Papua New Guinea. Annals of Botany 94(1):109-117.
Yang X, Barton HJ, Wan Z, Li Q, Ma Z, Li M, Zhang D, and Wei J. 2013. Sago-type Palms Were an Important Plant Food Prior to Rice in Southern Subtropical China. PLoS ONE 8(5):e63148.
