Acanthosicyos horridus (PROTA)

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Acanthosicyos horridus Welw. ex Hook.f.




Protologue: Benth. & Hook.f., Gen. pl. 1(3): 824 (1867).
Family: Cucurbitaceae

Synonyms

Vernacular names

Nara, nara bush, nara melon (En). Nara, melon nara (Fr). Nara (Po).

Origin and geographic distribution

Acanthosicyos horridus is endemic to the Namib Desert of the south-west coast of Africa and occurs from southern Angola, through Namibia to South Africa (north-western Namaqualand). The distribution of nara is limited to the coastal part of the Namib Desert where it grows exclusively in the sand dunes of mostly dry river beds where subsurface water is available. Before the introduction of maize into southern Africa, nara was a traditional staple food. Archeological evidence indicates that it has been a staple food for at least 8000 years, and was transported and perhaps even traded that long ago. It has not been domesticated and attempts to introduce it elsewhere have not been successful.

Uses

The seeds of nara, known as butter-nuts or butterpips, are eaten either fresh or roasted as a snack food, or ground into flour for cooking with other dishes. They are a good substitute for almonds, and have been exported to bakeries in Cape Town for use in confectionery. In Namibia ripe fruits, which are sweet and juicy and about 900 g in weight, are either eaten raw and relished for their high water content, or made into a traditional preserve, the dried fruit pulp being made into flat cakes. Nara is also eaten as a famine food.

Young stem tips are browsed by livestock. The bitter roots have medicinal value. Either chewed or made into a decoction, they are used to treat nausea, stomach-ache, venereal diseases, kidney problems, arteriosclerosis and chest pains. The crushed root mixed with fat is used to heal wounds. Oil from the raw or boiled seeds is used as a skin moisturizer and to protect the skin from sunburn.

Production and international trade

There is no commercial production of nara fruits. Trade in seeds between Namibia and South Africa has been reported, but no statistics are available.

Properties

The composition of the seeds per 100 g edible portion is: water 5.3 g, energy 2709 kJ (647 kcal), protein 30.7 g, fat 57.0 g, carbohydrate 2.3 g, crude fibre 1.3 g, Ca 100 mg, Mg 363 mg , Fe 4.0 mg, Zn 5.5 mg, niacin 2.2 mg. The composition of fresh fruits per 100 g edible portion is: water 84 g, energy 231 kJ (55 kcal), protein 1.4 g, fat 0.3 g, carbohydrate 11.7 g, fibre 1.0 g, Ca 21.4 mg, Mg 19.0 mg, P 22.4 mg, Fe 0.5 mg, Zn 0.6 mg, carotene 0.12 mg, thiamin 0.01 mg, riboflavin 0.02 mg, niacin 0.75 mg (Van den Eynden, V., Vernemmen, P. & Van Damme, P., 1992). The ripe fruits are aromatic and the pulp is rich in sugars. The fruit pulp and plant sap contain a non-volatile enzyme which curdles milk. A high percentage of the seed-oil is made up of polyunsaturated fatty acids, with a linoleic acid content of 53%.

Green unripe fruits contain varying amounts of highly oxygenated tetracyclic triterpenoids, called cucurbitacins. Cucurbitacins B and D have been identified as the primary source of bitterness, together with traces of cucurbitacins G and H. These compounds cause a burning sensation in the mouth. As the fruits ripen they rapidly lose their bitterness under the influence of the enzyme elaterase. The same four cucurbitacins are found in higher concentrations in the dried root. The bitter principles occur as aglycones in the fruits, but as glycosides in the roots. The LD50 of cucurbitacin B administered intraperitoneally to mice is 1 mg/kg, and this dose produces pulmonary oedema. The fruit juice contains germination inhibitors, which act to a large extent by an osmotic stress factor. The starches are of an unusually small size, which renders them suitable in the production of biodegradable plastics.

Description

Perennial, dioecious, strongly branched shrub up to 1 m tall and 15(–40) m in diameter, with a very long, woody taproot; stem longitudinally grooved, pale yellowish to pale green, spiny; spines in pairs, 2–3 cm long. Leaves reduced to minute scales, apparently absent. Flowers unisexual, regular, 5-merous, sessile or shortly stalked in spine axils; calyx campanulate, with ovate lobes, greyish hairy; corolla deeply lobed, lobes broadly ovate, c. 1 cm long, fleshy, pale yellow or pale green; male flowers solitary or fasciculate, with 3–5 stamens; female flowers solitary, with 5 elongate staminodes and inferior, ovoid ovary densely covered with oblong-conical, 2–2.5 mm long, soft spines, style columnar, with 3–5 two-horned flat or capitate stigmas. Fruit a subglobose berry up to 20 cm in diameter, covered with spiny protuberances, ripening from green to pale yellow or pale orange-yellow, many-seeded. Seeds embedded in yellow to orange-yellow pulp, oblong or ovoid, 12–16 mm × 7–11 mm × 5–7 mm, cream-coloured, hard with a thick testa.

Other botanical information

Acanthosicyos comprises 2 species and is placed in the tribe Benincaseae, together with important genera including Benincasa, Citrullus, Coccinea, Lagenaria and Praecitrullus. Acanthosicyos naudinianus (Sond.) C.Jeffrey differs notably from Acanthosicyos horridus in its creeping, annual, leafy stems.

Growth and development

Nara is able to survive in a hyper-arid desert climate because of its woody taproot that grows deep into the sand allowing it to reach subterranean water. It can survive in years without any rainfall and in some areas it is the only plant species found. A single nara shrub can cover an area of up to 1500 m2. Nearly 40% of the plant’s aboveground biomass is made up of spines, the rest of stems. In the absence of leaves, photosynthesis takes place in these spines and stems. The dense lattice-like growth of older stems serves to catch and bind windblown sand, acting as a dune stabilizer and thus the plant builds up its own dune micro-ecosystem. Male plants produce more flowers than the female ones and may flower nearly all year long, with a decline in flower production during early winter (May–July). Female plants flower from August–April, and their fruits mature from December–May. Having sticky pollen, nara is probably pollinated by insects. Germination has been reported by local inhabitants to occur only after rain. The age of mature fruiting nara plants may exceed 100 years.

Ecology

The coastal Namib Desert where nara is found receives extremely low and variable amounts of rainfall, the annual average not exceeding 100 mm, and in some years there is no rain at all. Precipitation is augmented by the frequent occurrence of fog. The distribution of nara roughly approximates the inland limits of the fog belt. Temperatures along the coast are fairly constant, the minimum averaging 16°C and the maximum 21°C. Due to the constantly shifting dunes, soil formation does not occur, thus presenting a nutrient-poor plant environment. The mineral composition of the dune sands is quartz, feldspar and garnet. Sands underneath nara plants are exceptionally low in nitrogen and phosphorus content. Other plants sometimes found growing in association with nara are the dune grass Stipagrostis sabulicola (Pilg.) De Winter, and the leaf succulent Trianthema hereroensis Schinz. Nara plays an important ecological role in the Namib Desert, providing shelter, food and water for many species of invertebrates, reptiles, mammals and birds, some of which are endemic and depend entirely on nara for their survival.

Propagation and planting

The 1000-seed weight of nara is about 300 g. Seeds germinate easily, but plants seldom flourish in cultivation.

Management

Nara fruits are collected from wild plant populations. They are neither cultivated nor domesticated. Attempts to domesticate the nara bush have been unsuccessful for reasons relating to its very specific habitat requirements. Each family of the Topnaar people of the Lower Kuiseb Valley near Walvis Bay, Namibia owns a number of nara bushes, which are considered private property, but not including the land they grow on. Harvesting is only allowed from the plants owned by the family concerned.

Diseases and pests

Harvesting

At the time nara fruits begin to ripen (from December onwards) many Topnaar families move to the nara fields to harvest and process the fruits. The harvesting can last until May.

Yield

Handling after harvest

The Topnaar people process the nara fruits into a preserve. Ripe fruits are collected and either buried in the soil or left in the sun for softening, after which they are peeled and then boiled until the seeds become loose. The pulp is allowed to thicken and turns into a dark orange colour. After separating the seeds, the thick remaining pulp is poured out and allowed to dry in the sun. It solidifies in a few days, forming flat leathery cakes, called ‘goa-garibeb’, which are then cut into strips or rolled up for storage. These fruity rolls have good keeping quality and can be chewed or added to porridge for the remainder of the year. The seeds are sieved from the boiled fruit flesh, dried in the sun and stored for eating, grinding into a flour, or sale to traders. Raw seeds are separated from the fruit pulp by rubbing them in the sand.

Genetic resources

Over the past 20 years there has been a reduction of possibly as much as one third in the size of the nara populations being harvested by the Topnaar along the Kuiseb River. The construction of a flood-retaining dam coupled with dune encroachment has stopped the flow of surface water. However, there are uninhabited areas along the coastal Namib Desert where nara still occurs abundantly. Germplasm of Acanthosicyos horridus is held at the National Plant Genetic Resources Centre, Windhoek, Namibia.

Prospects

Although today nara does not play as intrinsic a role in the lives of the Topnaar people as it did before, it remains an important part of their tradition and culture. Its protection should be a high priority to ensure human survival in the Namib Desert and for combating desert encroachment. Research is being undertaken in Namibia on the germination and possible cultivation of Acanthosicyos horridus to explore its cost-effectiveness as a crop. Namibian scientists are currently working with the Topnaar to sustain and improve the existing nara fields. There may be further potential in the seed trade, and marketing skills and techniques could enable the Topnaar to see a better income from the sale of nara seeds.

Major references

  • Craven, P. & Marais, C., 1986. Namib flora. Swakopmund to the giant Welwitschia via Goanikontes. Gamsberg Macmillan Publishers, Windhoek, Namibia. 128 pp.
  • Hylands, P.J. & Magd, M.S., 1986. Cucurbitacins from Acanthosicyos horridus. Phytochemistry 25(7): 1681–1684.
  • Jeffrey, C., 1980. A review of the Cucurbitaceae. Botanical Journal of the Linnean Society 81: 233–247.
  • SEPASAL, 2002. Acanthosicyos horridus. [Internet] Survey of Economic Plants for Arid and Semi-Arid Lands (SEPASAL) database. Royal Botanic Gardens, Kew, Richmond, United Kingdom. http://www.rbgkew.org.uk/ ceb/sepasal/acantho.htm. 28 February 2002.
  • Van Damme, P., 1998. Wild plants as food security in Namibia and Senegal. In: Bruins, H.J. & Lithwick, H. (Editors). The arid frontier: interactive management of environment and development. Kluwer Academic Publishers, Dordrecht, Netherlands. pp. 229–247.
  • Van den Eynden, V., Vernemmen, P. & Van Damme, P., 1992. The ethnobotany of the Topnaar. University of Gent, Belgium. 145 pp.
  • Wehmeyer, A.S., 1986. Edible wild plants of southern Africa. Data on the nutrient contents of over 300 species. Scientia, Pretoria, South Africa. 52 pp.

Other references

  • Botha, F.C. & Grobbelaar, N., 1981. Germination inhibitors in the fruits of some indigenous species of the Cucurbitaceae. South African Journal of Science 77(2): 79–81.
  • Enslin, P.R., 1954. Bitter principles of the Cucurbitaceae. I. Observations on the chemistry of cucurbitacin A. Journal of the Science of Food and Agriculture 5: 410–416.
  • Enslin, P.R., Joubert, F.J. & Rehm, S., 1956. Bitter principles of the Cucurbitaceae. III. Elaterase, an active enzyme for the hydrolysis of bitter principle glycosides. Journal of the Science of Food and Agriculture 7: 646–655.
  • Enslin, P.R., & Rehm, S., 1958. The distribution and biogenesis of the cucurbitacins in relation to the taxonomy of the Cucurbitaceae. Proceedings of the Linnean Society of London 169(3): 230–238.
  • Enslin, P.R., Rehm, S. & Rivett, D.E.A., 1957. Bitter principles of the Cucurbitaceae. VI. The isolation and characterization of six new crystalline bitter principles. Journal of the Science of Food and Agriculture 8: 673–678.
  • Klopatek, J.M. & Stock, W.D., 1994. Partitioning of nutrients in Acanthosicyos horridus, a keystone endemic species in the Namib Desert. Journal of Arid Environments 26(3): 233–240.
  • Meeuse, A.D.J., 1962. The Cucurbitaceae of southern Africa. Bothalia 8(1): 1–112.
  • Sandelowsky, B.H., 1990. Acanthosicyos horridus, a multipurpose plant of the Namib Desert in southwestern Africa. In: Bates, D.M., Robinson, R.W. & Jeffrey, C. (Editors). Biology and utilization of the Cucurbitaceae. Cornell University Press, New York, United States. pp. 349–355.
  • Sandelowsky, B.H. & Cambry, R.G., 1988. Namibia yesterday, today and tomorrow. In: Whitehead, E.E., Hutchinson, C.F., Timmermann, B.N. & Varady, R.G. (Editors). Arid lands today and tomorrow. Proceedings of the international research and development conference, October 1985, Tucson, Arizona. Westview Press, Boulder, United States. pp. 1121–1125.
  • Schrire, B.D., 1987. Cucurbitaceae, orthographic ambiguity clarified. Bothalia 17(2): 181.
  • Versfeld, W. & Britten, G.F., 1915. Notes on the chemistry of the Naras (Acanthosicyos horrida Hook.). Report of the South African Association for the Advancement of Science 12: 232–238.
  • Watt, J.M. & Breyer-Brandwijk, M.G., 1962. The medicinal and poisonous plants of southern and eastern Africa. 2nd Edition. E. and S. Livingstone, London, United Kingdom. 1457 pp.

Sources of illustration

  • Sandelowsky, B.H., 1990. Acanthosicyos horridus, a multipurpose plant of the Namib Desert in southwestern Africa. In: Bates, D.M., Robinson, R.W. & Jeffrey, C. (Editors). Biology and utilization of the Cucurbitaceae. Cornell University Press, New York, United States. pp. 349–355.

Author(s)

  • M.H. Wilkins-Ellert

4246 W. Flying Diamond, Tucson, Arizona 85742, United States

Correct citation of this article

Wilkins-Ellert, M.H., 2004. Acanthosicyos horridus Welw. ex Hook.f. [Internet] Record from PROTA4U. Grubben, G.J.H. & Denton, O.A. (Editors). PROTA (Plant Resources of Tropical Africa / Ressources végétales de l’Afrique tropicale), Wageningen, Netherlands. <http://www.prota4u.org/search.asp>.

Accessed 1 December 2017.