A nut is defined as a "hard and indehiscent 1-seeded fruit" (Jackson, 1926). For the purpose of this survey, the definition has been stretched to include fruits with more than 1 seed and even, in one case, (Pangium), a berry, but one in which the seed is large, oily, and is treated like the kernel of a nut.
The kernel of an edible nut is the seed; it may include endosperm, usually oily or starchy, or it may be an embryo only. It often contains a large amount of fat, making it a concentrated energy food, and is usually a useful source of protein, vitamins and minerals. The seeds of plants often contain toxic substances; some seeds, used as food, are poisonous in various degrees, and must be processed in some way to make them safe to eat.
Trees require little care, so nut-bearing trees are an asset to village people. Some nuts have potential as exports, but no trade has developed so far.
The coconut, Cocos nucifera, is, for the present, ignored. It has its specialists and a very extensive literature. Breadfruit, Artocarpus communis, J.R. and G. Forst., is no more a nut than Pangium, but its seed could be regarded as one. However, discussion of this genus, with Parartocarpus, can hardly be confined to a short paper. Only woody plants are considered here; the peanut, Arachis hypogaea L., is therefore excluded.The following plants (arranged in family order, following Hutchinson, 1959) are discussed:
|Pandanus jiulianettii Martelli||Family||Pandanaceae|
|Inocarpus fagifer (Parkinson) Fosberg||"||Leguminosae|
|Castanopsis acuminatissima(Bl.) A.DC.||"||Fagaceae|
|Pangium edule Reinw.||"||Flacourtiaceae|
|Finschia chloroxantha Diel;||"||Proteaceae|
|Macadamia integrifolia Maiden and Betche||"||Proteaceae|
|Aleurites moluccana (L.) Willd.||"||Euphorbiaceae|
|Omphalea gageana Pax and Hoffm.||"||Euphorbiaceae|
|Terminalia catappa L.||"||Combretaceae|
|Terminalia impediens Coode||"||Combretaceae|
|Terminalia kaernbachii Warb.||"||Combretaceae|
|Canarium indicum L.||"||Burseraceae|
|Canarium kaniense Lautb.||"||Burseraceae|
|Anacardium occidentale L.||"||Anacardiaceae|
Pandanus jiulianettii Martelli
Tree 10-30 m high, branched, with large prop-roots; trunk diameter to 30 cm. Leaves strap-like, to 3 m long x 10 cm broad, with upward directed prickles along the margins and midrib. Flowers dioecious, male or female on separate trees. Male flowers whitish in dense spikes, soon withering; no perianth, stamens numerous. Female flowers in dense heads; no perianth, ovary 1-celled and containing 1 ovule, surmounted by a flat stigma. In fruit the heads (syncarps) are ellipsoid, 30-35 cm long, 25-30 cm in diameter, on a stout stalk. The individual fruits (drupes) are up to 10 cm long, 1.5 cm across; when ripe, they separate from one another easily. The weight of a mature head, with stalk, is recorded as 16 kg (Bowers, 1963).
The kernel (seed) consists mainly of oily endosperm, with a small embryo. When fresh, it has a flavour resembling coconut, but sweeter. It becomes rancid rather quickly, without treatment. In highland houses, the nuts are stored above the fireplace. Presumably some drying takes place, which would slow down deterioration.
The species is endemic to New Guinea, and is found throughout the mainland. In cultivation, it is reported from 1500 to 2500 m. Wild plants occur in the higher part of this range; their nuts are not (or very little) used. There are intermediate forms, with useful kernels which are, however, hard to extract. These plants are preserved, and sometimes transplanted to more convenient positions, but not given further care. Superior plants are carefully tended. These also are variable, and some have nuts with a 'soft' shell which is easily broken in the fingers.
Pandanus is important to highland people, from both nutritional and cultural viewpoints. In addition, trunks and prop roots are used in building, and leaves as thatch. Those of P. jiulianettii are considered to be superior to most in the 'karuka' group, at least in the Western Highlands (Bowers, 1963).
Pandanus conoideus Lamk, a 'marita', is much cultivated, but its fruit cannot be considered as a nut, since it is the endocarp, outside the pyrene (stone) which is used as food.
Inocarpus fagifer (Parkinson) Fosberg [Aila (P), Tahitian Chestnut (E)]
Tree, to 30 m, but most specimens seen are from 10-20 m; trunk usually fluted; branches somewhat pendulous. Leaves simple, alternate, more or less oblong, rather large, 10-40 cm long. Flowers bisexual, white, small, in simple or branched spikes from the axils; calyx 2-3 lobed, petals 5, alike, joined at the base, 1-1.5 cm long. Fruit indehiscent, irregularly flattened - ellipsoid, often ribbed, yellowish-orange when ripe, 6-10 cm long, 5-10 cm wide, to 4.5 cm thick; one-seeded. Seed to 7 cm long, 5-7 cm wide, about 3 cm thick.
The seed is eaten after roasting or boiling. An analysis of the seeds gave 7% of fat, 10% protein, 80% non-nitrogenous substances (which would be mainly starch) and 2.5% ash (Burkill, 1966). According to the same source the seed is best eaten slightly before maturity.
The tree is cultivated throughout the coastal regions of Malesia and on the Pacific Islands. It may be found throughout Papua New Guinea at low altitudes, mainly near the sea or along large rivers. Wild populations occur, and another species, I. papuanus Kostermans, has been described; its seed is much smaller than that of I. fagifer and it does not seem to be used at all. The fruit is dispersed by bats, which gnaw the pericarp. The seed is often damaged by insect larvae.
Castanopsis acuminatissima (BI.) A.DC.
A tree to 35 m tall, often with numerous coppice shoots about the base. Leaves simple, alternate, ovate-lanceolate to elliptic, acuminate, 5-15 cm long, dark shining green above, brownish or silvery beneath. Flowers separately male and female, monoecious (both sexes on the same tree). Male flowers very small (to 2 mm long), light brown or cream coloured, in slender spikes (catkins) 5-10 cm long. Female flowers greenish, scattered on an axis to 10 cm long. The nut, as it develops, is enclosed in a rough, woody cupule. At maturity the nut is ovoid, pointed, brown, slightly hairy, about 1.5 cm long, and emergent from the cupule for about half its length. The single seed is composed mainly of 2 large cotyledons.
The kernel is eaten, at least in some areas; there are not many reports. The nut is small; entire, it weighs less than 1 g, the kernel less than ½ g. At Okapa, Eastern Highlands, it was recorded as "eaten raw or cooked in bamboo" (Hamilton, 1956). From Pomio, East New Britain, it was reported that the seeds were commonly eaten after boiling, and that some children, against the advice of their elders, persistently ate raw kernels; this seemed to lead to mouth ulcers, emaciation and anaemia (Baalen, 1960). These effects could be due to the presence of tannins, often found in members of the family Fagaceae.
C. acuminatissima occurs from India to China and Taiwan, throughout Malesia to New Britain. In Papua New Guinea it is widespread, often common, in mountain forest from 500 to 2500 m. The wood, which is durable in its habitat, and splits easily, is used for building and fencing.
Pangium edule Reinw.
Smallish to large trees, specimens to 40 m are recorded; usually buttressed, with a dense crown. Leaves large, 10-40 cm long, ovate cordate, dark green, shining above. The tree is polygamous-dioecious; male and female inflorescences are on different trees, but a male inflorescence may have one or more flowers (the highest ones) bisexual, so 'male' trees also bear fruit. Male flowers in short racemes; petals 5-8, pale green, about 2 cm long, stamens 20 or more. Female flowers usually solitary, the petals somewhat larger than in the male flowers; staminodes (sterile stamens) few or up to 20. Fruit ellipsoid or more or less pear-shaped, 15-25 cm long, with a brownish, rather rough surface. Seeds up to 20, closely-packed, irregularly triangular-ovoid, mostly 4-6 x 2-3 cm, enclosed in a white fleshy aril. The seed-coat is hard and ribbed; it is greyish when fresh and darkens when weathered. The white flesh of the kernel consists mainly of oily endosperm.
The whole tree is rich in hydrocyanic acid, and is therefore extremely poisonous; a few fresh leaves in a jar make an effective killing-bottle for insects. The fresh leaves or seeds, or oil from the seeds are used as insecticide and antiseptic, and to preserve meat (Slewner, 1954). The oil from the seeds is used for cooking, lighting and for making soap. The flesh of the seeds is widely used as food, but must be carefully processed, by roasting, washing in water, underground storage, etc., before its final preparation as food. The seed-coats are used as rattles in sing-sings.
The tree occurs throughout Malesia, the Bismarck Archipelago and the Solomons, and in the New Hebrides and other Pacific islands, in forest, or preserved on cleared land, sometimes semi-cultivated. In Papua New Guinea it is found from sea level to 1000 m.
Finschia chloroxantha Diels
Tree to 30 m tall, but 5 m specimens have been seen flowering and 1.0-40 cm long, parchment-like or somewhat leathery. Flowers bisexual, light golden yellow, in racemes from the axils or from leafless branches.
A tree in full flower can be spectacular. Fruit more or less compressed globose, 3-5.5 x 2.5-4.5 cm, yellow at maturity, soon turning black; exocarp thin, fleshy, endocarp hard, woody. Seeds 2, flattened, circular in outline; cotyledons thick, fleshy.
The seeds are eaten after cooking, and are apparently widely used, throughout the range of the species. A single seed (rather a small specimen) was found to weigh just over 3 g.
The species occurs throughout New Guinea and the Solomons, on the Aru Islands and in the New Hebrides; it is also reported from Palau Island, Micronesia. In Papua New Guinea it is widespread, from low altitudes to above 1800 m. It is sometimes planted near villages.
Macadamia integrifolia Maiden and Betche [Queensland nut]
A tree forming a dense, rounded crown, 20 m or more tall. Leaves lanceolate with toothed margins, to 30 cm long, solitary, paired or in whorls of 3. Flowers bisexual, in racemes to 30 cm long, off-white. Fruit about 2.5 cm across, the leathery exocarp dividing into 2 valves at maturity; nuts spherical, brown, shining, about 2 cm across. The kernel is white, pleasant-tasting, and may be eaten raw or cooked.
A native of Australia, the species has been cultivated commercially, there and in the Hawaiian Islands. The shell is fairly thick and very hard, but a 'soft-shelled' variety was developed in Hawaii and is now available in Australia. The tree could not be expected to thrive in Papua New Guinea at low altitudes, but should do well between 500 and 1500 m. A specimen was seen in 1950, in the Hube area of the Finschhafen subdistrict, Morobe Province, at an altitude of about 1000 m. The ground underneath the tree was littered with broken shells, and the nut was praised by the local people; "like coconut". Nevertheless, it has been very little planted.
Aleurites moluccana (L.) Willd. [Candle nut]
Tree, to 30 m tall. Leaves alternate, often crowded near the branch-tips, variable in shape and size, from small and lanceolate to large, broad and lobed; when young, densely greyish-hairy, the hairs falling from the upper surface as the leaf ages, so that mature leaves are dark green above, greyish green beneath. Flowers small, white, in dense terminal panicles, separately male and female, monoecious (both male and female flowers on the same tree). Fruit to 5 cm across, fleshy, enclosing a single nut. Nut irregularly globose, ridged at one end, about 3 cm across. Shell 3 mm thick, very hard; kernel white, soft, oily, weighing up to 5 g in local specimens.
The nuts contain a moderately poisonous toxalbumen (Burkill, 1966) and may produce severe vomiting and diarrhoea if eaten raw, though they are sometimes eaten without ill-effects (Everist, 1974). In Papua New Guinea they are usually roasted before eating. In Hawaii they are roasted, powdered and mixed with salt and chilli as a relish (Neal, 1965). The oil from the seed is a drying oil, but slower to set than linseed oil; it is the main oil for paint in China (Burkill, 1966). The nuts, threaded on a skewer of bamboo or wood, will burn like a candle, hence the name.
A. moluccana is native in the Moluccas, New Guinea and Australia, and naturalised elsewhere. It is cultivated throughout Malesia to India and China, and in the Pacific. In Papua New Guinea, it occurs from low altitudes to about 2000m.
Omphalea gageana Pax and Hoffm.
A large woody vine, high-climbing; red sticky exudate from the wood when cut. Leaves alternate; juvenile leaves deeply 5-10 lobed; adult leaves simple, elliptic to ovate, 7-20 cm long, the tips blunt or acuminate; 2 small glands at the base of the petiole. Inflorescence a panicle, with linear leaflike bracts to 5 cm long; these are characteristic. A monoecious species; flowers separately male and female, but on the same plant, the male flowers on lateral parts of the panicle, the female flowers more or less central; all flowers small, yellowish green. Fruit slightly broader than long, about 6 x 5 cm, with 3 rounded lobes; pericarp thick, fleshy. Seeds, 3, irregularly flattened-orbicular, about 2.5 x 1.5 cm, covered, when fresh, with a cream-coloured aril; seed-coat 1-1.5 mm thick, hard, ridged, brown; kernel white, consisting of copious endosperm surrounding 2 broad, thin cotyledons.
The kernel is eaten after cooking, either alone or as a relish with other food. A single kernel, fresh, weighs about 3 g.
The genus Omphalea occurs in America, Africa, Asia and Malesia; O. gageana is endemic to New, Guinea, so far as is known. There are not many collections, probably because the vine is usually inaccessible in the forest canopy; it seems common enough in the Lae area, and is said to be much-used in the Milne Bay Province. Most reports are from low altitudes, but it is known from Okapa (Eastern Highlands) at about 1800 m.
Terminalia catappa L.
Tree to 40 m, but usually much less; branches in whorls, more or less horizontal. Leaves obovate, fairly large, to 25 x 15 cm; the old leaves turn light brown or red, and a few red leaves can usually be seen in the crown. Flowers bisexual in small terminal spikes, white or cream coloured, about 3 mm long. Fruit flattened-ellipsoid, 5-7 x 3-4 cm, usually surrounded by a ridge or flange; pericarp fibrous, rather spongy, the inner part hardened to a stone around the seed. Seed white, mainly, composed of the leafy, coiled cotyledons.
The kernel is edible, but is not much used; it is very small, about ¾ g, and not easy to extract. It yields an oil said to compare with almond oil (Brown, 1951), but commercial production seems unlikely.
T. catappa occurs naturally from tropical Asia to Australia and Polynesia, and is now planted throughout the tropics. It is found in most coastal regions of Papua New Guinea, as a beach tree, and planted in towns and villages.
Terminalia impediens Coode
Tree to 40 m tall; branches in younger trees horizontal, in whorls, finally making a spreading crown with heavy branches; twigs thick. Leaves clustered at twig-tips, obovate, mostly about 20 cm long, 10 cm wide, sometimes with reddish-brown hairs beneath. Flowers about 7 mm long, bisexual, whitish green, in spikes. Fruit red or purplish-red when ripe, ellipsoid, about 8 x 5 cm, the outer part fleshy-fibrous, the inner part a thick woody stone, which splits on germination into 2 unequal parts. Seed about 5 x 1 cm, spindle-shaped, mainly composed of 2 coiled, leaf-like cotyledons.
The kernel is edible. It has a pleasant taste and can be eaten raw; the weight, fresh, varies from 1 to 1½ g. The fruits may be left until the outer fibrous covering has rotted away; the stones then are not difficult to break.
The tree is endemic to New Guinea and has been reported mainly from the north western part of Papua New Guinea, the Sepik, Madang and Morobe Provinces, with a few collections from the Central and Gulf Provinces. It occurs in lowland forest; there is no evidence that it is cultivated, but trees are preserved when land is cleared for gardening. In the forest, trees can be located by the stones from the fruit, which lie on the ground for a long time before they decay.
Terminalia kaernbachii Warb. [Okari]
Trees similar in appearance to T. impediens. Leaves clustered at the twig-tips, obovate, 20 x 10 cm more or less, with persistent reddish-brown hairs beneath. Flowers in erect spikes, usually densely hairy. Fruit ellipsoid, somewhat flattened, about 10 x 7 x 5 cm, red or purplish-red when ripe, outer part fleshy-fibrous, inner part a thick woody stone, which splits into two almost equal parts at germination. Seed to 8 x 2 cm, with 3-4 coiled, leaflike cotyledons.
The kernel is of high quality, and sought after as a food. It appears that the tree has a long history of cultivation and selection; smaller kernels weigh only l½ g, other up to 15 g. The flavour may be improved by light roasting, with salt; this may also improve the keeping quality. The nuts could certainly be sold overseas if they could be exported in good condition, but at present the production is barely sufficient for local needs.
The species is endemic to New Guinea; records of wild specimens are known, from lowland forest in the southeastern part of Papua New Guinea (Coode, 1978). It is preserved in garden land, and cultivated near villages. It has also been planted in Australia and Sri Lanka, and possibly in America.
Canarium indicum L. [Galip]
Tree to 40 m tall, buttressed. Leaves alternate, compound, with 3-8 pairs of leaflets and a terminal leaflet; leaflets 7-35 x 3½-16 cm, often acuminate; persistent stipules at the base of the petiole, varying in shape, 4 cm long x 1½ x 3 cm wide, or much larger, margin more or less fringed. Dioecious, flowers male or female on separate trees; inflorescence a terminal panicle; petals 3, free, creamy-yellow, in male flowers about 1 cm long, in female flowers to 1.5 cm long, hairy. Ovary 3-celled, but usually only one seed develops. Fruit blackish purple when ripe, ovoid, round to slightly triangular in cross-section, to 6 cm long x 3 cm across. The fleshy endocarp dries and splits to expose the nut, to 5.5 cm long, 2 cm across, brown, smooth, rounded triangular in section with more or less acute ribs at base and apex. Seed 1, the other ovary-cells flattened; endosperm absent, cotyledons lobed.
The kernel is of high quality, and may be eaten raw or lightly roasted. Average specimens weigh about 3 g. One analysis shows the main constituents as 72% fat, 13.5% protein, 7% starch; the seed-coat should not be eaten, as it carries some substance producing diarrhoea (Burkill, 1966). The nut is important as an item of diet for village people, and can find a ready sale in towns. As with okari, the production of galip does not really meet local demand. It could have export potential, but the kernels become rancid rather quickly. The nuts of cultivated races vary in size and quality; the species would no doubt repay investigation and selection.
C. indicum is native to the Moluccas, New Guinea, the Bismarck Archipelago, the Solomon Islands and the New Hebrides, and is cultivated in eastern Malaysia and the Pacific. In Papua New Guinea it is widespread in lowland forests and improved races are cultivated, particularly in the Bismarck Archipelago and the Madang Province.
The name C. indicum appears in literature as occurring in western Malesia, but the species there has been separated as C. vulgare Leenhouts; on the ground that Linnaeus used a mixed collection as the type. In C. indicum the stipules have toothed or fringed margins, and remain in place until the leaves age; in C. vulgare the stipules have entire margins and fall early, and the trees are more slender in all their parts (Leenhouts, 1959).
There is a lengthy discussion in Burkill (1966) under the name Canarium commune L. This is an illegitimate name, published later than C. indicum L., for the same material. As used by Burkill it applies both to C. indicum and C. vulgare.
Canarium kaniense Lauterbach
Tree to 40 m, sometimes with buttresses. Leaves similar to those of C. indicum, leaflets acuminate; stipules not long-persistent, elliptic to obovate, 1-8 x ½ to 4 cm, the margins toothed or fringed. Flowers a little larger than in C. indicum. Fruit ovoid, 5-6 x 3-4 cm, blue-black when ripe. Nut 4-5 cm long, sharply triangular, 2-2½ cm across.
The species is endemic to New Guinea, so far only collected in the eastern part, at altitudes from sea level to 1000 m. The variety globigerum Leenhouts has globose fruits about 5 cm across, the nut rounded-triangular in the basal part, sharply angled near the tip. The kernel is oily with a pleasant taste. The tree is apparently cultivated in the Northern and Morobe Provinces.
Anacardium occidentale L. [Cashew nut]
A small, branching tree. Leaves alternate obovate, 6-15 x 4-7 cm, dark green, leathery. Flowers in spreading panicles, polygamous, with male and bisexual flowers on the same tree. Petals pink, 1-1.5 cm long; stamens 7-10, one longer than the others; ovary 1-celled. Fruit a kidney-shaped nut, about 2.5 cm long, borne on a pedicel which at maturity is about 5 cm long, fleshy, yellowish and edible. Seed about 2 cm long, oily.
The kernel, which is soft, with a pleasant flavour, is a major article of commerce in some countries. The skin of the nut contains phenolic compounds which may cause blistering of the skin; individuals vary in their susceptibility and seem to become sensitised by successive contacts. The irritant substances are volatile and are removed by roasting the nuts before processing; the fumes may cause inflammation of mucous membranes. The 'cashew-apple', the succulent fruit-stalk, may be eaten fresh, in preserves, or used for making wine or vinegar. It causes irritation of the throat in susceptible people.
The cashew nut is native to tropical America. It is now widely cultivated throughout the tropics, and industries have developed in Africa (at least in primary production) and India (where the nuts are processed). The tree does well in the more fertile areas of lowland Papua New Guinea, but no sort of industry has developed.
The nut-like fruits of several other wild trees are used in Papua New Guinea, e.g. Heritiera littoralis Dryand., along foreshores, Elaeocarpus womersleyi Weibel in mid-mountain regions, and the seeds of Sterculia schumanniana (Laut.) Mildb. in the lowlands. However, they do not show much potential for improvement. The list could no doubt be expanded considerably. There are also nuts overseas which could be introduced, including the Brazil nut and its allies. Some attention to selection and propagation of indigenous species, and introduction of desirable exotics, could considerably increase this valuable food resource.
Note: Clark et al. (1951) examined the fat of Okari nuts. Air-dried kernels contained about 70% fat (cf. galip), 12% protein and 10% "N-free extract". Tannin content of the fruits was found to be negligible.
The fat was pale yellow (darker from damaged kernels) with a melting point of 32°C. The main fatty acids were palmitic, 37%, stearic, 7-8%, oleic, 34% and linoleic, 15% (expressed as glycerides).
DATE: January 1982
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