Metroxylon rumphii Mart.

Metroxylon sagu is a palm tree, without leaf sheaths; boles have a diameter of 35-60 cm and reach a height of 6-16 m. Starch is stored in the central parenchyma of the bole. Under prolonged flooding conditions, it forms pneumatophores. The true sago palm is a pinnate-leaved tree. Healthy palms carry about 24 leaves or fronds. Each month a new frond appears out of the growing point, and the oldest dies. Sago palm is also hapaxanthic; each bole heralds the end of its life cycle by developing a huge branched terminal inflorescence with a large quantity of fruit. The trunk decays after the formation of the fruit and 1 or more suckers from the trunk take over. The generic name is from the Greek ‘metro’ (the pith of the tree), and ‘xylon’ (wood), referring to the large amount of internal pith.

Sago palm is hapaxanthic, that is, it flowers only once during its life; after fruiting, the leaves senesce and the plant dies completely. There are hermaphroditic and male flowers. The palm can be classified as a nearly complete obligatory cross-breeder, with easy vegetative multiplication. The vegetative growth phase lasts for at least 8 years before the tree flowers.

Clay soils with a high organic-matter content give best results.

Occurring in the hot humid tropics of Southeast Asia and Oceania, sago palm dominates mainly in permanent or seasonal lowland freshwater swamps, preferably on mineral soils with a pH higher than 4.5. Ideally, groundwater should be within 50 cm of the soil surface. Mixed with upland trees, it can also be found on dry soils, where it grows even taller.

M. sagu is indigenous to Indonesia (where it is now probably only cultivated), New Guinea and the Solomon Islands, among other places. It was probably introduced into some of the islands such as Rotuma and Samoa by aboriginals, and more recently into other islands.

M. sagu propagates itself both vegetatively and sexually. Propagation of cultivated stands occurs only vegetatively, through suckers, mostly growing from the lowest leaf axils, because the palm is harvested before flowering. The suckers have the advantage of being readily available and of producing homogeneous offspring, which allows selection. The palm also propagates itself sexually at the end of its life cycle. The inflorescence may contain up to 850 000 fruits. The seed germinates only under wet conditions. A rosette grows from the seed, out of which a new bole and new suckers may be formed.

Farmers plant relatively small and quick-maturing varieties on clay soils high in organic matter at 7 x 7 m, giving about 200 stumps/ha. In the 2nd year of trunk formation, about 100 suckers/ha (which developed in the 1st year) should be selected for starch production. Harvesting for maximum starch per trunk should be timed to coincide with the onset of fruit formation. Once the tree is planted, it produces a regular succession of suckers from the lowest part of the trunk, forming a cluster of various stages of development. Suckering is regulated by pruning, so that each cluster palm produces 1 bole every 18 months.

Pests and diseases have not seriously affected sago palm, but with increasing intensity of cultivation they are likely to increase. Some pests recorded include the hispid beetle (Botronyopa grandis), whose larvae feed on young tissues of the unopened spear at the central base of the crown; termites, which may become a pest on peat soils containing undecomposed vegetative matter; and the red-striped palm weevil (Rhynchosporus spp.), whose eggs may be deposited on young plants with exposed injured tissues. The larvae burrow into these tissues.

The species has been classified as recalcitrant. If suckers are not planted directly, they are kept for 2-3 months in a well-shaded nursery. This is also done if suckers are to be transported any distance.

Reclamation: Sago palm has been planted in buffer zones as a method of rehabilitating degraded lands, for instance the coastal plains of Indonesia where thousands of hectares of land had been abandoned. Soil improver: The waste from pith processing is used as a fertilizer.

Food: The boles of sago palm have always been used to obtain starch as a staple food for humans. Hot water is poured over the slightly sour wet starch and stirred. The resulting gluelike mass is eaten with fish and vegetable dishes, for example. The growing point and the young leaves around it may be used as a vegetable, the palm heart or cabbage. Grubs, especially of Rhynchosporus spp., may grow in decaying trunks, and sago growers consider them a delicacy. Fodder: Ground pith is sometimes used as an animal feed, especially for pigs, and when dried, for horses and chickens. Fuel: Dextrose sugar extract from sago palm starch can be processed to yield power ethanol. The cortex of the trunk is also used for firing in paper mills. The bark may be used as a domestic fuel after drying. Fibre: Processing of the pith to yield starch produces a fibre. The leaves also yield a fibre, which may be used for mats. Other products: The rice-straw mushroom (Volvaria volvacea) is cultivated on waste from sago extraction, the frond rachis is often used for fastening between horizontal posts in walls, and the bark may be used as a flooring material.