Gnetum (New)

Introduction

Gnetum africanum, commonly known as African joint fir or eru, is a plant species that belongs to the family Gnetaceae and the genus Gnetum. It is one of the several species within the genus Gnetum. The genus comprises approximately 35 species of small trees, shrubs, or most often lianas, found in tropical South and Central America (about 7 species), Africa (2 species), and Asia (about 25 species). They look much like dicotyledonous flowering plants (having opposite leaves with a net venation and cherry-like seeds), although they are gymnosperms. The 2 African species G. africanum and G. buchholzianum, are very similar and have been classified in section Gnetum. They are found in humid tropical forests ranging from Nigeria to Cameroon, the Central African Republic, Gabon, the Democratic Republic of the Congo, and Angola. The two species are quite similar and can only be distinguished by the shape of the leaf and the characteristics of the reproductive structures. In its cultivation zones, Gnetum leaves form a very popular and highly valued vegetable; they are often picked from the wild and sold at local markets, where they are frequently a significant commodity. The plant is highly regarded for its nutritional value, as it is rich in essential nutrients such as vitamins, minerals, and proteins. The leaves of Gnetum africanum are commonly used in traditional African dishes, including soups, stews, and sauces. The plant is highly regarded for its nutritional value, as it is rich in essential nutrients such as vitamins, minerals, and proteins.
In addition to its culinary applications, Gnetum africanum also possesses medicinal properties. It has been traditionally used in African herbal medicine for various purposes, In Nigeria, eru is used for treatment of piles and high blood pressure and also as medicine against enlarged spleen, sore throat and as a purgative. In the Central African Republic, the leaves are eaten to treat nausea and as an antidote to arrow poison made from Periploca nigrescens Afzel. In Cameroon the leaves are chewed to mitigate the effects of drunkenness and they are taken as an enema against constipation and to ease childbirth. They are also used to treat boils and fungal infections on the fingers. The supple stem is sometimes used as rope. Gnetum africanum often commands lower market prices than G. Buchholzianum because of its thinner and paler leaves. Additionally, the leaves are exported to ethnic marketplaces throughout the world. Current harvesting methods are unsustainable, so research is being conducted on economically producing the plant. (Schippers & Besong,, 2004, Mialoundama, 1993).

Species accounts

Both African Gnetum species (Gnetum africanum and Gnetum buchholzianum are dioecious (with plants being either male or female) lianas with two different types of stems. The orthotropic (vertical) ones have small, scale-like leaves and rapidly grow vertically, reaching main branches of a tree where they produce stems with fully developed leaves. The stem continues climbing until it reaches the canopy where it branches into several leafy stems. Female plants often show more vigorous growth with stronger stems than male plants. Eru continues to grow during the dry season and new shoots may develop where the stem has been cut or where side shoots have been removed. Under wild conditions, both species grow and form underground tubers or roots that store plant food reserves. These can remain alive for many years when the vegetation and the Gnetum vines above ground are cleared and the soil surface is laid bare. The distinctly coloured drupe-like seeds are probably dispersed by birds and other animals.

G. africanum leaves are relatively thin, light to pale green, and ovate to oblong in shape. The male catkins are of equal width from the base to their tip. G. buchholzianum leaves are elliptic to oblong in shape, thick and dark green. It produces catkins with a diameter decreasing from the base to the top internode (Schippers, 2004). The dry matter content of fresh Eru leaves is much higher than for other dark or medium green leafy vegetables. This gives a feeling of firmness during preparation, leading some customers to view eru as a meat replacement. Gnetum africanum is threatened with disappearance because of intensive gathering and cultural activities which are destroying the forests that support the plants. Possible adoption into farm systems is a step on the right way to conserving this plant (Orwa et al., 2009, Schippers, 2004).
Ecological requirements
Eru can be found in the rain forest from sea level up to about 1200 m altitude and prefers an annual rainfall of about 3000mm. 
Gnetum africanum and Gnetum buchholzianum thrive in a wide range of habitats, including farm fallows or abandoned farmland, secondary forests, and closed forest. The vines of both Gnetum species climb supporting big and small trees, dead trees, saplings, shrubs, other climbing vines such as rattan palms, and a host of other plant materials in the complex tropical humid forest, where they grow luxuriantly and produce significant quantities of leaf biomass. It is usually found on middle and under-storey trees together with other climbers and frequently forms thickets. It can also be found in riverine forest areas that are otherwise too dry for the species. Gnetum africanum is mainly found at the periphery of primary and secondary forests. Gnetum buchholzianum is primarily found in the forest, especially near openings created by fallen trees (Asaha, 2000, Mialoundama 1993, Shiembo, 1996, Shiembo, 1999, Schippers, 2000).
Agronomic aspects 
Seed germination is slow and irregular; germination periods of 1 year or more are pretty normal. Even so, the germination percentage is very low in a nursery. It is assumed that seeds need pretreatment, such as passing through the intestines of a bird, fruit bat, squirrel, or other animals, before they germinate. Seed is typically found only in the tree canopy. Seed collection is thus far from easy, a reason why eru is hardly cultivated.
The cheapest propagation method available is rooted cutting. Fresh stem cutting is taken, for which a stem with a single pair of leaves is adequate. These cuttings are placed in well-decomposed sawdust as a rooting medium, and care is taken to keep the leaves moist. A mist system is ideal for this purpose, although not essential, and other means of keeping the leaves wet with a fine spray if water can also be used.
Evapotranspiration of the new cuttings should be minimized and it is recommended that the plant bed be covered with fine gauze, nylon net, or a loosely woven piece of cloth. Once rooting has taken place, which may take about a month, the new plantlets should be transferred to a proper growing medium with forest soil. Polythene sleeves filled with soil can be used for this purpose. Once side shoots have developed from the nodes, plants should be given more space to create an adequate flow of air 
After about 6 weeks, the rooted cuttings are transferred to polythene sleeves, bamboo pots, or other containers, where they remain for a further 2-3 months. The soil mixture for these containers consists of 25% sand and some compost, supplemented with forest soil. Field planting occurs at the beginning of the rainy season, preferably next to a young tree or shrub.

Management
Eru is mainly collected from wild stands; farmers often retain it when clearing fields. If cultivated, farmers need to provide support, e.g., by using commercial plantations of rubber trees, oil palm, and other crops. The use of fences was only found to be successful when there is enough shade, and it is generally too expensive. Fully exposed plants do not grow well; their leaves are thin and pale green. In experiments, nutrients, especially nitrogen, have shown a positive effect on growth and rate of leaf development.

Harvest, post-harvest practices

The current method of harvesting, especially for export trade, is by either uprooting whole plants or pulling the stems from the trees. This leads to large-scale destruction of natural stands. Occasionally, trees have to be cut to reach leafy stems in the canopy. This is mainly done during the dry season when the forest is more accessible and where there is little work on the farm. Controlled harvesting in which only side shoots or parts of stems are collected is clearly better than destructive harvesting. After such harvesting, new shoots may develop where a stem has been cut or where side shoots have been removed. Preliminary observation indicates that 3-4 harvests per year are possible, whilst still allowing substantial regrowth. More frequent harvesting will result in thin leaves that are considered inferior. 
The first harvest may take place 6-9 months after planting and the total lifespan of eru is estimated at over 10 years.

Post-harvest practices
Leaflet stems of eru remain fresh for at least a week. Branches collected from the forest are brought to collecting points from where they are sold in the local markets or exported. For this trade, whole leafy stems are packed in large bales. Selection takes place on the size and texture of the leaves, which is mainly dependent on the species. Gnetum buchholzianum is more popular with consumers and expensive because its leaves are generally thicker than those of Gnetum africanum. The fresh leaves are somewhat leathery and are thus tough to eat whole. The leaves are therefore shredded into strips about 2 mm wide. This product can be prepared directly or dried for later use after reconstitution by soaking in water. This shredding process is done by placing several leaves on top of each other and cutting them with a sharp knife. It is a tedious job that is often done before export, mainly to black communities of Nigerian and Cameroonian origin in the U.S. and the U.K. (Schippers and Feeday, 1998).
Gnetum is often eaten as part of a mixture in a groundnut-based stew. It often replaces meat because of its high protein content and is thus much appreciated. To soften the otherwise tough product, people mix Eru with waterleaf, Talinum fruticosum, and these two vegetables are always eaten together.

Value addition, and market value 
Preservation of Gnetum
Chopped well-dried leaves are packaged in containers e.g. in polythene bags and stored in room temperature. They may keep well for about 1 year. The stored leaves are soaked in hot water prior to cooking.
In trade, consignments of Gnetum africanum and Gnetum buchholzianum are often mixed. Traders will pay more for the thick dark green leaves of the latter, but much variation is also caused by growing conditions. Most eru is consumed locally, but intensive trade has developed from Cameroon and more recently also from Gabon and the Central African Republic to meet the large demand in Nigeria. Most eru from Cameroon, Gabon and the Central African Republic is transported to Idenau, a coastal village in Cameroon, and from there by boat to Nigeria. Estimates for the annual export of eru leaves (both species) to Nigeria range between 2500 t and 4000 t. Another major marketing centre is the Koilo Region in Congo. Other marketing centres in Cameroon are Campo near Kribi for export to Gabon and the Mfoundi market in Yaoundé. Dried shredded leaves are exported, mainly from Nigeria to the United States and to a lesser extent from other countries to France and the United Kingdom (Schippers, R.R. & Besong, M.T., 2004).

Nutritional value and complimentary recipes 

Gnetum africanum is rich in fiber (28–37%) and protein (13–18%). The plant is high in carbohydrates -38–44% dry matter. Other values based on 100 g dry weight of leaves indicate: carbohydrates 70 g, of which 40 g is cellulose, protein 16.5 g, lipids 6 g and ash 7 g. The caloric value for G. africanum leaves therefore is much higher than in most vegetables, 248 to 307 kcal/100 g (Ali et al. 2011). The high protein and fat content of eru leaves explain why it is often used as a substitute for meat. The protein of Eru has all eight essential amino acids (isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine). This nutrient composition of Gnetum varies depending on the variety. The nutritional value of Gnetum buchholzianum is often higher than that of Gnetum africanum.

Proximate composition and level of nutrients in Gnetum leaves prepared in different ways

1Data in %. Source: AVRDC & IPGRI, 2006
2 Data in ppm. Source AVRDC & IPGRI, 2006. To convert to %, divide by 10000.
3Chemical composition of G. africanum (% of dry matter), Ali et al. 2011 (Ali, Fadi & Assanta, Mafu & Robert, Carole. (2011). Gnetum africanum: A Wild Food Plant from the African Forest with Many Nutritional and Medicinal Properties. Journal of medicinal food. 14. 1289-97. 10.1089/jmf.2010.0327.)
 4Chemical composition of G. africanum in %. Source: Ali et al. 2011.
RE=retinol equivalents. 
RAE =Retinol activity equivalents. A RAE is defined as 1μg all-trans-retinol, 12μg beta-carotene, or 24μg α-carotene or β-cryptoxanthin.
a Lewis, J. 2019. Codex nutrient reference values. Rome. FAO and WHO
b NHS (refers to saturated fat)
c https://www.hsph.harvard.edu/nutritionsource/water/
d British Heart Foundation
e FDA
f NIH
g Mayo Clinic

Complimentary recipes

1. Fumbwa (Kikongo, Lingala)
(DRC recipe of Gnetum)
Ingredients
1 teaspoonful salt
1 green pepper
4 tablespoonfuls of palm oil
8 tomatoes 
1 magii cube (seasoning)
10 teaspoonfuls peanut butter
2 onions, medium size 
300 g smoked fish
4 cups water

Preparation
Wash leaves and cut them into small pieces
Bring water to boil and then soak the leaves
Wash the leaves 3 times in the hot water
Heat palm oil and add all ingredients at once i.e. tomatoes, peanut butter, flavoring cube and smoked fish
Mix all the ingredients, add salt to taste and then add water
Cook in low fire till the vegetable is soft. This may take up to 2 hours
Serve with manioc or maize fufu. One may also eat with chikwangue

Remarks 
The Bakongo people of west DRC like this vegetable. They have however influenced other communities living in the capital, Kinshasa. Note also that, this preparation requires a lot of peanut butter and cooking because it is coarse.

2. Gnetum africanum with palm oil and peanut. 
Ingredients
•    500 g (or more) of Gnetum africanum, or substitute any other greens: Cassava leaves, collards, kale, turnip greens or similar; or spinach; cleaned, stems removed; and shredded, finely cut, or pounded in a mortar with a pestle 
•    one cup peanuts (or peanut butter) 
•    one or two ripe tomatoes, peeled and chopped (or canned tomato paste, or canned tomato) 
•    one leek (or one onion), finely chopped 
•    one piece of dried, salted, or smoked fish (the size of your hand), bones and skin removed, cleaned, soaked in water, and rinsed 
•    one cup red palm oil

Preparation procedure
•    Place the greens in a large pot. Add enough water to partially cover. Bring to a boil. Reduce heat, (do not cover), and simmer until greens begin to become tender. (Cooking time varies considerably depending on type of greens used.) Add water if pot becomes dry.
•    Grind, chop, or pound peanuts into a fine paste. (Or you can start with natural, sugar-free peanut butter.)
•    When greens are mostly tender and liquid is reduced, add tomatoes (or tomato paste), leek (or onion), and dried fish. Continue to simmer, on low heat, stirring occasionally. Simmer until everything is tender and ready to eat. 
•    Remove a cup of the pot liquid and combine it with the peanut paste in a bowl. Stir to obtain a smooth sauce. Stir the peanut sauce into the greens, and reduce heat to as low as possible. Top with red palm oil and simmer for a few more minutes. 
•    Serve with boiled yams or sweet potatoes and/or cassava tuber, banana leaf or rice. 
Source: http://www.congocookbook.com/c0219.html

Genetic resources
Eru is hardly cultivated at all at present. There is still massive exploitation of the remaining natural stands, which have almost disappeared in Nigeria and are becoming scarce in Cameroon, Gabon, and the Central African Republic. There is an urgent need to collect and preserve the diversity found within the two African Gnetum species, preferably throughout their natural range (AVRDC & IPGRI, 2006.) 

Prospects
Alternatives to destructive harvesting of eru should be found. Once the new methods of propagation and cultivation have been adopted, there will be scope for the development of eru as a new crop, for which there is already high demand and an attractive price could be paid. The diversity found between accessions is considerable, offering scope for improving quality and productivity (AVRDC & IPGRI, 2006).