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Plants & People: The Intersection of Botany and Human Experience

Irvingia Gabonensis seedling

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Irvingia Gabonensis: The Untapped Diversity of Dika Plant Irvingia gabonensis is a multipurpose, undomesticated fruit tree native to West and Central Africa. Belonging to the family of Irvingiaceae, this evergreen tree species can grow to a height of 40 meters and attain a diameter of about 120 centimeters. The tree produces mango-like fruits that are well known for their nutritious kernels. Even though the fruit of this plant is also referred to as the African bush mango, the plant has no connection to the actual mango fruit. The dika tree can be found in the dry and wet tropical zones such as Nigeria, Angola, Uganda, Congo, Cameroon, Ghana, Togo, and Benin. It is also known to grow in farmland areas, semi-deciduous forests, and gallery forests. Despite its obscurity on the international level, this species should hardly be considered a minor resource. Almost all parts of the plant have a use from its fruit to its bark. Additionally, it serves as a main source of food and income for indigenous groups in Africa such as the Baka tribe from Central Africa. Due to how prized this plant species is, the dika plant is left untouched by the indigenous people when forests are cleared. Once domesticated, the plant can potentially be used to treat the high levels of malnutrition in Africa. Yet, with increasing local and regional demand for the plant’s kernels, the African bush mango has been facing intense exploitation. Additionally, the disappearance of local wildlife such as elephants are affecting the plant’s dispersal. As a result, the I. gabonensis plant has been classified as a highly endangered species. By Ian Morris and Nikhitha Nair #dika
Nomenclatural History
This is an interesting species with many, many, many names. Just a few can be seen below.
Indigenous Names (people/country: local name)
Hausa: Agbalo; Nigeria: oro, oba, abesebuo, goron biri, moupiki, muiba, eniok, andok; Ibo: ogbono (kernels); Afemai (Edo State of Nigeria): ogi (fruit of I. gabonensis); Yoruba: apon; Cameroon: andok; Batanga (language in prime dika country near Kribi, Cameroon): mbumbwe’bo, nja’a; Congo: meba, mueba; Cwondo: Aadok; Ny: Abisibou; Kiaka: Aiya iyon; Mvae: Ando; Bulu (or Boulou): Ando’o; Bolon, Fang, Gabon: Andok; Temne: An-Gbere; Akyé: Bè; Mende: Boboi; Bateke: Boubwé; Dogose: Bwiba bambale.
Common Names (people/country: local name)
Sierra Leone: bobo; Côte d’Ivoire: boboru, wanini; English: bush mango, wild mango, dika, dika nut; French: manguier sauvage, chocolatier
Linnaean binomial
Irvingia barteri Hook.f, Irvingia caerulea Tiegh., Irvingia duparquetii Tiegh., Irvingia erecta Tiegh., Irvingia fusca Tiegh., Irvingia griffonii Tiegh., Irvingia hookeriana Tiegh., Irvingia laeta Tiegh., Irvingia pauciflora Tiegh., Irvingia platycarpa Tiegh., Irvingia tenuifolia Hook.f., Irvingia velutina Tiegh.
Evolutionary History
Locally, the different irvingia fruits are often referred to as payo in general. There are differences among them, but there is not much historical information on the evolution of these species. However, it is known now that these relatives speciated in “diversity ‘hot spots” (Lowe et al., 2000). These are zones in which there is high genetic diversity within these similar species.

This range is mainly contained to west-Central Africa. Countries included are Ghana, Nigeria, Cameroon, and Gabon being the main locations in which they are found (Leaky, 2017). However, in Cameroon is thought to be where this center of genetic diversity originates from (Leaky, 2017).
This is thought to be caused by the Pleistocene refugia dynamics. In simpler terms, there has not been a large influence of climate change since the Pleistocene era.

This means there has been a relatively constant environment, leading to species having relatively similar attributes due to them being the best adaptations for fitness (Lowe et al., 2000). They are varied just slightly enough to allow for niche partitioning and stable distribution. The main difference between our species and those that are closely related to it is that Irvingia gabonensis fruit is sweet and fleshy, while its relatives’ fruits are bitter and inedible (PROTA4U, 2017).
Ecology & Life History
This species is an important food source for many animals in the forest. The mammals of central Africa find this to be extremely nutritious. These mammals include a diversity of species including forest elephants, squirrels, red forest pigs, etc (Ainge & Brown, 2001). This is due to the kernels of the fruit being high in nutrients such as lipids and fats. Gorillas find the fruit itself to be their favorite part of the plant. Lastly, bees thoroughly enjoy the nectar of the flower and find it necessary in their production of honey (Ainge & Brown, 2001).

That being said, insects are the most important pollinator of this plant. The plant itself flowers twice a year, so there is plenty of time for pollination season. There are two obvious peaks of flowering, the height of the dry season in January, and the wet season in October (Ainge & Brown, 2001).

However, the fruiting time of this plant is less variable, with there being a range of fruiting twice a year, in accordance with the flowering times, all the way to slowing down to fruiting once every two years (Ainge & Brown, 2001). However, the trees begin flowering after reaching maturity. This usually takes about ten to fifteen years, but sometimes they can begin to bloom as early as six years old (Ainge & Brown, 2001).

Morphological Description of Vegetative Attributes
In general, this species is very large. They grow up to 40 meters tall, and have a meter wide buttresses that grow to nearly 3 meters high (PROTA4U, 2017). The bark is scaly and heartwood soft, with both being a green-yellow to gray. Also, the inner bark is fibrous and of an intense yellow (PROTA4U, 2017). Not only are there different textures throughout the wood, it is also quite dense, making them prone to shrinkage.The leaves themselves are simple, elliptical, leathery, thin, pinnately veined, and alternate up the stem (PROTA4U, 2017).

There is a possibility that they can be propagated vegetatively, especially for those that want to create communities of trees with favorable phenotypes (ie bigger fruits) (Leakey, 2017). However, there are limits on the age of the actual cuttings able to propagate. This is because while juvenile cuttings tend to be able to grow and provide a large amount of fruits, when the shoots are already mature, it is harder for them to mature even more into full trees and provide a similar amount of fruits as the juvenile cuttings (Leakey, 2017).
Morphological Description of Reproductive Attributes
The most essential parts of the reproductive attributes are the fruit, the kernal, and the nut. The nut encloses the kernel in a thin shell. This kernel is mostly made up of the endosperm, which of course contains most of the reproductive nutrition. It is soft, so it needs to be contained by the nut to protect it. Lastly, the fruit surrounds the entirety of it, with its fibrous flesh being tightly coated by its skin (Ainge & Brown, 2001).
Like stated before, the fruit of Irvingia gabonensis is sweet and fleshy, especially when compared to its most closely related taxa, Irvingia wombulus. This cousin actually used to be considered the same species until relatively recently, mainly due to its distinctive bitter fruit (Leakey, 2017). Something to note is that it is impossible to predict the size of kernels from the size of the fruits, as there is no correlation between them (Leakey, 2017). This makes it hard for the future of cultivation, as it is hard to choose between desired phenotypes because they are both agriculturally important. Future research is needed to explore these relationships to see if there is any correlation in hopes of eventually domestication of this species.
Expanding on the nutritiousness of the fruit, it is known to be a very good source of many minerals, such as vitamin C (Ainge & Brown, 2001). As aforementioned, it is popular with the wild life as they have adapted to obtaining many of their supplements from this fruit. Similarly, the composition of the seeds are known to be full of lipids and fatty acids. In fact, it is thought that this part of the tree is the most valuable in terms of nutrition. They are highly thought of when it comes to being an oil seed (Ainge & Brown, 2001). In general, these species provide many essential nutrients necessary for all animals, including humans, to thrive.
Cultivation + Domestication Potential

At present, the African bush mango is considered to be in the early stages of domestication. All species of Irvingiaceae occur naturally in the forests of West and Central Africa. Typically, African farmers prefer to maintain adult bush mango trees already growing on their lands or in forest areas (Ainge & Brown 2001). Yet, if they choose to directly plant I. gabonensis, its seeds will take at least fourteen days to germinate; additionally, if the seed is directly extracted from the fruit, it must be dried for two days before planting (Ainge & Brown 2001). It takes around ten years for this Irvingia species to even start producing fruit(Ainge & Brown). Thus, it has been recognized that if the Irvingia gabonensis was to be domesticated and farmers want to gain a faster financial return from this plant, more efficient methods of propagation are needed. Some propagation methods that have been looked into include cuttings, marcotting, and bud grafting (Ainge & Brown 2001).
Historical Accounts
Even though historically many indigenous tribes in West and Central Africa have interacted with the ogbono plant, it has been heavily linked to the Baka tribe of Central Africa. The Baka are an indigenous group who inhabit the tropical forests of south-eastern Cameroon, northern Republic of the Congo, northern Gabon, and southwest of the Central African Republic; they mainly survive on hunting, gathering, and fishing (Schulman 2016). Given that more than 50% of the Baka’s daily caloric intake comes from eight Irvingia species including Irvingia gabonensis during fruiting season, Irvingia gabonensis is an important Baka food source (Gallois et al., 2020).
Additionally, Irvingia gabonensis has been documented to play a major role in Baka well being and culture. Since the hunting of large mammals such as elephants, gorillas, and chimpanzees is now prohibited by law in Central Africa, collecting bush mangoes is the main reason why the Baka continue to stay in their traditional forest camps for longer periods of time; time spent in these forest camps is necessary for the transfer of ecological knowledge as children of the Baka get to directly interact with their environment and can benefit from the storytelling taking place in these camps at night (Gallois et al., 2020).
The sale of Irvingia fruits is also a major source of income and empowerment for the Baka community. The trading of dika kernels is the only major transaction in which this group directly receives money; the sale of the other two main traded goods, cacao and timber, provides money to the Nzimé tribe, who then share the proceeds with the Baka (Gallois et al., 2020). Furthermore, cacao and timber are principally managed by men; so for women, particularly single women, their income primarily comes from dika kernel collection (Toda & Yasuoka 2020). I. gabonensis is also a convenient cash income source for schoolchildren. As the fruiting season from July to August coincides with the vacation period, children staying in town to go to school will return to the village and spend time selling dika kernels (Toda & Yasuoka 2020).

Current Uses and Consumption of the Dika Plant
Seed Prized for its versatility and high price, dika seeds are traded all across Africa. It was calculated in 1980, the cost of dika kernels collected from a single dika tree was the equivalent of three hundred US dollars (National Research Council 2006). The seed itself can be consumed raw or roasted; however, it is typically pounded into a paste called “dika butter” which has a similar texture to that of peanut butter (National Research Council 2006). In Nigeria, this paste is commonly used as a soup thickening agent (Onyekwelu & Stimm, 2014). In Central Africa, the seed is processed to create Dika bread, Dika cake, and Gabon chocolate (Onyekwelu & Stimm, 2014). Outside of food, the oils from the Dika seed are used in soap making, cosmetics, and pharmaceuticals (Onyekwelu & Stimm, 2014).

Fruit The fruit of the Irvingia gabonensis resembles a mango and can be eaten fresh (Onyekwelu & Stimm, 2014). It can also be processed into jellies, jams, juices, and sometimes wine (Onyekwelu & Stimm, 2014). The fruit pulp is also used to prepare black dye for cloth (Obidike 2021).
Leaves The leaves of the ogbono plant can be boiled for tea or taken as an extract to reduce fever; it is also used as food for livestock (Onyekwelu & Stimm, 2014).
Bark The bark of the plant has many medicinal applications. Shavings of the bark can be consumed to treat diarrhea, hernias, yellow fever, and dysentery; it can also be boiled to relieve toothache (National Research Council 2006).
Nutritional Value
The popularity of the African bush mango plant in West and Central Africa is also due to the nutritional benefits it can provide. The kernel of the plant is found to be rich in vitamins and minerals such as calcium, iron, phosphorus, and sodium (McPherson 2021). Additionally, it has high levels of protein and oil, including six out of the eight essential amino acids (National Research Council 2006). Even though most of the nutritional value of this plant comes from its seed, the fruit of the plant also provides more vitamin C than oranges and lots of carotenoid antioxidants (McPherson 2021).
Human Experience
Due to the nutritional and cultural value of the Irvingia gabonensis plant, it has been the focus of several development initiatives. In 1996, I. gabonensis was noted to be a priority species for domestication and already village-level nurseries are being created for dika plants in Nigeria and Cameroon (National Research Council 2006). If successfully domesticated, one potential use of the African Bush Mango plant would be to reduce levels of chronic malnutrition. As noted before, the kernels of the African Bush mango are high in oil and protein. These characteristics would make it a great dietary supplement in Central and West Africa where marasmus and kwashiorkor is common among babies (National Research Council 2006).
However, access to the Irvingiaceae population is being challenged by social and ecological pressures such as unsustainable harvesting and disappearance of wildlife. The increasing demand for Dika kernels nowadays has led to unsustainable gathering methods such as felling trees (Gallois et al., 2020). Additionally the decrease in large mammals like elephants in African forests threatens the spread of dika seeds; it has been found that it takes longer for the ogbono plant to germinate when it is not passed through an elephant gut (Gallois et al., 2020). Due to their mobility, the Baka tribe might take over the role of being the main dispersers of dika seeds in forest areas; yet, they won’t be as sufficient as the local wildlife are in maintaining the dika plant population (Gallois et al., 2020). Therefore, conservation efforts should be made in the future to keep this cultural and ecological keystone species alive.

References
Ainge, L., & Brown, N. (2001). IRVINGIA GABONENSIS & IRVINGIA WOMBOLU - A State of Knowledge Report undertaken for The Central African Regional Program for the Environment.
Gallois, S., Andel, T., Heger, T., & Sonké, B. (2020). Comparing Apples and Pears: the Hidden Diversity of Central African Bush Mangoes (Irvingiaceae). Retrieved May 28, 2022, from https://www.researchgate.net/publication/342789634_Comparing_Apples_and_Pears_the_
Hidden_Diversity_of_Central_African_Bush_Mangoes_Irvingiaceae
Leakey, R. R. B. (2017). Quantitative descriptors of variation in the fruits and seeds of Irvingia gabonensis. Multifunctional Agriculture, 227–233. https://doi.org/10.1016/b978-0-12-805356-0.00021-0
Lowe, A. J., Gillies, A. C., Wilson, J., & Dawson, I. K. (2000). Conservation genetics of Bush Mango from Central/West Africa: Implications from random amplified polymorphic DNA analysis. Molecular Ecology, 9(7), 831–841. https://doi.org/10.1046/j.1365-294x.2000.00936.x
McPherson, G. (2021, June 22). African mango: Nutrients, benefits, and downsides. Healthline. Retrieved May 28, 2022, from https://www.healthline.com/nutrition/african-mango#the-fruit
National Research Council. (2006). Lost Crops of Africa: Volume II: Vegetables. 6 Dika | Lost Crops of Africa: Volume II: Vegetables |The National Academies Press. Retrieved May 28, 2022, from https://nap.nationalacademies.org/read/11763/chapter/8
Obidike, J. (2021, November 1). Ogbono (African Mango): 6 Amazing Benefits, Nutrition, and Side Effects. Healthful Wonders. Retrieved May 28, 2022, from https://www.healthfulwonders.com/ogbono-african-mango-benefits-nutrition-side-effects/
Onyekwelu, J., & Stimm, B. (2014). Irvingia Gabonensis. Retrieved May 28, 2022, from https://onlinelibrary.wiley.com/doi/abs/10.1002/9783527678518.ehg2006012

PROTA4U. (2017). Irvingia gabonensis (Aubry-Lecomte ex O'Rorke) Baill. PROTA4U. Retrieved May 25, 2022, from https://www.prota4u.org/database/protav8.asp?g=psk&p=Irvingia+gabonensis
Toda, M., & Yasuoka, H. (2020, March). Unreflective promotion of the non-timber forest product trade undermines the quality of life of the baka: Implications of the IRVINGIA gabonensis kernel trade in southeast Cameroon. 1Library. Retrieved May 28, 2022, from https://1library.net/document/zl1x77ry-unreflective-promotion-undermines-implications-irvingia-gabonensis-southeast-cameroon.html