Common Name: Oysternut

General Information

Oysternut is a vigorous, evergreen climbing plant, producing stems 30 metres or more long from a thick, tuberous, deep root system. The stems become woody with age and up to 10cm in diameter, scrambling over the ground and climbing into the surrounding trees where they attach themselves by means of tendrils[, ].
The plant is an important food source in central, eastern and southern Africa, also providing medicines, oil and a polish. It is harvested from the wild and is also often grown commercially for its seed in central and eastern Africa, though it is seldom seen elsewhere in the tropics[, ]. It produces large fruits that can weigh 14 kilos and contain up to 70 seeds[].

Known Hazards

None known

Botanical References

,

Range

Tropical Africa - Tanzania, northern Mozambique.

Habitat

Coastal rain and riverine forest from sea level to 1,100 metres[].

Properties

Weed Potential	Yes
Edibility Rating
Medicinal Rating
Other Uses Rating
Habit	Evergreen Climber
Height	20.00 m
Growth Rate	Fast
Pollinators	Insects
Self-fertile	No
Cultivation Status	Cultivated, Wild

Cultivation Details

Oysternut grows best in lowland, humid tropical areas at elevations up to 1,000 metres[]. It can be cultivated at elevations up to 1,800 metres, though yields start to fall the more the elevation increases above 1,000 metres. It grows best in areas where annual daytime temperatures are within the range 23 - 28°c, but can tolerate 14 - 38°c[]. It prefers a mean annual rainfall in the range 1,500 - 2,000mm, but tolerates 1,200 - 2,500mm[].
Succeeds in full sun and in light shade[]. Tolerant of a wide range of well-drained soils[, ], though a humus-rich, fertile soil gives the best yields[]. Prefers a pH in the range 5.5 - 6, tolerating 5 - 7[]. Plants produce a deep taproot and, once established, are very drought resistant[, , ]. Plants are often trained to grow into trees[]. They greatly dislike exposure to strong or cold winds[].
This species has high weed potential[].
Young plants grow very quickly, producing stems up to 7 metres long in 6 months and 15 metres long in 18 months[].
Flowering normally commences 15 - 18 months after planting out the young plants[]. Female and male plants cannot be distinguished until they flower[].
The fruit takes 5 - 6 months to ripen from flowering[].
When fruits ripen they split open gradually. To attain full flavour, the seeds should be allowed to ripen in the fruit and be collected 7 - 10 days after the fruit begins to split[].
The plant produces up to 30 gourds in its third year and can continue production for another 20 years[, ].
Under good conditions, two harvests per year are possible, and flowers and fruits can be present at the same time[].
Annual seed yields of 3 - 7 tonnes per hectare have been achieved[, ].
The fruits burst when ripe, scattering the seeds[].
Care must be taken when growing these plants to choose sufficiently large trees for them to grow into, since their weight, especially when bearing a crop of fruits, can be enormous[].
A dioecious plant, both male and female forms must be grown if seed is required[]. Generally 12 - 15 males per hectare are sufficient to fertilise a plantation of females[]. There are reports that female plants can produce fruit and seed in the absence of a male plant by a process called apomixis[].

Edible Uses

Seed - raw or cooked[]. A soft but firm texture with an excellent flavour[]. The seed can be used to replace almonds or brazil nuts in confectionery and are also used in a variety of food dishes by local people[]. The seed is usually roasted[]. The seed contains about 30% protein[] and has a high oil content[]. It is irregularly circular in shape, about 4cm in diameter and 12mm thick[]. It is easily extracted from its shell[]. Seeds can be stored in their shells for several years in good condition[].
To remove the bitter principle, whole seeds can be soaked for 8 hours in 3 changes of water. To remove the kernel from the shell, the fibrous husk is first partly cut away, then the shell is cracked and opened using a knife[].

An oil extracted from the seed has a pleasant, slightly sweet flavour[]. It makes a good cooking oil[]. The seed contains up to 61% oil[]. It is important to remove the husk of the seed before extracting the oil since it contains an intensely bitter substance that could contaminate the oil[, ].

Medicinal

The seeds are said to have valuable galactagogue properties and are in great demand amongst native mothers who consume them shortly after the birth of a child as a tonic in order to regain their strength and also to improve the flow of milk[, ].

The oil obtained from the seed is used as medicine for stomach troubles and rheumatism[].

Agroforestry Uses:

Oysternut is part of the rich agroforestry systems of Mount Meru and Mount Kilimanjaro in Tanzania, where it is grown in combination with coffee and banana[].

Other Uses

The oil extracted from the seed can be used to make soap, candles and cosmetics[, , ].

The fibrous husk of the seed is sometimes used for polishing native earthenware pots[].

Propagation

Seed - it has a short viability and is best sown as soon as ripe. Repeated soaking and drying promotes germination[]. The seed can be sown in situ or in containers[]. The drip line of trees is a favoured site for planting in situ[]. When grown in containers, sow 2 - 3 seeds in each container thinning to the strongest plant once they germinate. The seed usually germinates in 7 - 14 days[]. Seedlings grow away quickly and are ready for planting out about 30 days after germinating[].
Layering. Very easy[].
Cuttings. Stemcuttings root in 2 - 3 weeks, and produce shoots 6 - 7 weeks after planting[].

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