PROTA, Introduction to Vegetables

PROTA 2, 2004. Plant Resources of Tropical Africa. vol. 2. Vegetables. ed. by G.J.H. Grubben & O.A. Denton. Wageningen, PROTA Foundation - Backhuys - CTA. 668 p.

Choice of species

This PROTA 2: Vegetables book describes the cultivated and wild vegetable species of tropical Africa. Some of these are only used as a vegetable, but others have two or more uses. PROTA assigns one primary use and if relevant, one or more secondary uses to all plant species used in Africa. PROTA 2: Vegetables comprises only accounts of species whose primary use is as a vegetable. The primary use of baobab (Adansonia digitata L.) is as a leafy vegetable, and thus it is treated in PROTA 2, but it has several secondary uses, e.g. the fruit is eaten, oil is extracted from the seed, the wood is used for timber and fuel, the bark for fibre, and the bark and fruit for the preparation of medicines. Also cassava (Manihot esculenta Crantz) is quite important as a leafy vegetable, but its primary use is undoubtedly its edible starchy root, and consequently cassava is described in PROTA 8: Carbohydrates.

Species that are used as a vegetable but also have another primary use are listed after the primary use vegetables, and are fully described in other commodity groups. Some important species included in this list are: Ipomoea batatas (L.) Lam., Manihot esculenta Crantz, Parkia biglobosa (Jacq.) R.Br. ex G.Don, Solanum tuberosum L. and Xanthosoma sagittifolium (L.) Schott.

The definition of a vegetable as ‘succulent plant parts consumed as side dish with a starchy staple food’ is simple and clear at first sight. However, it is difficult to unambiguously delineate the commodity group vegetables, and the boundary with other commodity groups is sometimes arbitrary, e.g. that with commodity group spices and condiments. Capsicum pepper (Capsicum annuum L.) is used in fairly large quantities as a vegetable or in small quantities as a spice, depending on the capsaicin content of the fruits. Garlic is another example of a multipurpose plant, sometimes considered primarily a spice or medicinal plant, but treated in the commodity group vegetables.

A few leguminous species grown for their dry seeds can be important vegetables as well, i.e. for the consumption of immature seeds, green pods and/or leaves. Pea (Pisum sativum L.) and cowpea (Vigna unguiculata (L.) Walp.) are included in PROTA 2: Vegetables, but also in PROTA 1: Cereals and pulses. A special group are some Cucurbitaceae, e.g. melon and watermelon, the fruits of which are eaten raw. Because of their annual growth habit and cultivation as field crops these are conventionally included in PROTA 2: Vegetables and not in PROTA 6: Fruits. In addition, several Cucurbitaceae species grown for their dry seed, eaten as side dish or snack are treated as vegetables.

In PROTA 2: Vegetables comprehensive descriptions are given of about 110 important vegetable species. These major vegetables comprise most cultivated species, but also several wild or partly domesticated species. The accounts are presented in a detailed format and illustrated with a line drawing and a distribution map. In addition, accounts of some 170 vegetables of minor importance are given. Because information on these species is often scanty, these accounts are in a simplified format and do not include a drawing or map.

Plant names

Family: Apart from the classic family name, the family name in accordance with the Angiosperm Phylogeny Group (APG) classification is also given where it differs from the classic name.

Synonyms: Only the most commonly used synonyms and those that may cause confusion are mentioned.

Vernacular names: Only names in official languages of regional importance in Africa are included, English, French, Portuguese and Swahili. It is beyond the scope of PROTA to give an extensive account of the names of a species in all languages spoken in its area of distribution. Checking names would require extensive fieldwork by specialists. Although regional forms of Arabic are spoken in several countries in Africa, the number of African plant species that have a name in written, classical Arabic is limited. Arabic names are therefore omitted. Names of plant products are mentioned under the heading ‘Uses’.

Origin and geographic distribution

To avoid long lists of countries in the text, a distribution map is added for major species. The map indicates in which countries a species has been recorded, either wild or planted. It should be realized that for many species these maps are incomplete because they are prepared on the basis of published information, the quantity and quality of which varies greatly from species to species. This is especially the case for wild species which are not or incompletely covered by the regional African floras, and for cultivated species which are only planted on a small scale (e.g. in home gardens). For some countries (e.g. Central African Republic, Chad, Sudan, Angola) there is comparatively little information in the literature. Sometimes they are not covered by recent regional or national floras and although species may be present there, this cannot be demonstrated or confirmed. For some major species, a distribution map has been omitted because there is too little information on distribution.

The assortment of market vegetables in African countries varies largely. In urban areas the 25 most important cultivated vegetables account for up to 90% of the total consumption of 100–150 g/person, whereas vegetables collected from the wild account for less than 5%. In rural areas the variation is greater and more wild vegetables are consumed. Large differences exist not only between urban and rural areas, but also between forest and savanna zones, lowland and highland regions, countries and tribes, and more generally between West, Central, East and Southern Africa and between Anglophone, Francophone and Portuguese-speaking countries. As an illustration of this location-dependent variation a list of the most important market vegetables is presented in Table 1. It shows differences between the West African forest zone (Lagos) and the savanna or Sahel area (Kano), between West Africa (Nigeria) and East Africa (Kenya) and between lowland (Mombasa) and highland (Nairobi). Many temperate-type vegetables are traded in West Africa from the savanna zone to the forest zone, and in East Africa from highland to lowland regions.

Table 1. Availability and relative importance of vegetables in urban markets in Nigeria (West Africa) and Kenya (East Africa)

Scientific name	common name	Nigeria		Kenya
		Lagos	Kano	Nairobi	Mombasa
Abelmoschus caillei	West African okra	+++++	++++	0	0
Abelmoschus esculentus	okra	+++++	+++++	+++	+++++
Adansonia digitata	baobab	++ *	+++++	0	++
Allium cepa	bulb onion, shallot	+++++ *	+++++	+++++	+++++ **
Allium fistulosum	welsh onion	+++	++++	++	+ **
Allium sativum	garlic	+++ *	+++++	++++	+++ **
Amaranthus cruentus	amaranth	+++++	+++++	+++++	+++
Amaranthus dubius	amaranth	++++	++	+	++++
Basella alba	Ceylon spinach	++++	++	+	++
Brassica oleracea	headed cabbage	+++ *	+++++	+++++	+++++ **
Brassica oleracea	cauliflower	+++ *	+++++	++++	+++ **
Brassica oleracea	leaf cabbage	0/+	0/+	+++++	+++ **
Capsicum annuum	chilli pepper	++++	+++++	+++	+++++
Capsicum annuum	bird pepper	++++	+++++	+	++
Capsicum annuum	aromatic hot pepper	+++	+++++	+	++
Capsicum annuum	sweet pepper	++++ *	+++++	++++	++++
Celosia argentea	celosia	+++++	++	0	+
Citrullus lanatus	watermelon	+++	+++++	+++++	+++++
Citrullus lanatus	egusi melon	+++++	+++++	0	0
Cleome gynandra	spiderplant	0	0	++++	+++
Corchorus olitorius	jew’s mallow	+++++	++++	+++	++++
Cucumis melo	melon	+++	++++	+++	+++
Cucumis sativus	cucumber	++++	+++++	+++	+++
Cucurbita maxima	pumpkin	+++	+++++	++++	+++
Cucurbita moschata	musk pumpkin	+++	+++++	+++	+++
Cucurbita pepo	courgette	+++	+++++	+++	+++ **
Daucus carota	carrot	+++ *	+++++	++++	++++ **
Hibiscus sabdariffa	roselle	+++	+++++	0	+
Lactuca sativa	lettuce	++++	+++++	+++++	+++
Lagenaria siceraria	bottle gourd	++	++++	++	++++
Lycopersicon esculentum	tomato	+++++*	+++++	+++++	+++++
Moringa oleifera	drumstick tree	+	+++++	+	+++
Phaseolus vulgaris	French bean	+++	+++++	+++++	++++ **
Raphanus sativus	radish	++	++++	++	+
Solanecio biafrae	worowo	++++	+	0	0
Solanum aethiopicum	garden egg (Gilo Group)	+++++	+++	++	++++
Solanum aethiopicum	ndrowa (Kumba Group)	++	+++++	0	0
Solanum macrocarpon	gboma	++++	++	0	+
Solanum melongena	eggplant	+++	+++++	++++	++++
Solanum spp.	African nightshades	++++	++++	+++++	++++
Talinum triangulare	waterleaf	++++	++	0	0
Telfairia occidentalis	fluted pumpkin	+++++	+++	0	0
Vernonia amygdalina	bitterleaf	+++++	+++	0	0
Vigna unguiculata	cowpea (leaves)	+++	++++	+++	++++

0 absent; + rare; ++ occasional; +++ common; ++++ important; +++++ frequent, large quantities.

* = supply from savanna area, northern Nigeria (shallot and tomato also from southern Nigeria);

** = supply from highland Kenya.

Properties

Vegetables are eaten for their flavour (relishes) and nutritional value. The content of micronutrients (vitamins, minerals) is of major importance, but in many cases also the macronutrients (carbohydrate, protein, fat) contribute considerably to the nutritional value of the meal. The nutrients that are essential components of the diet are listed in the species accounts. The analytical method used to determine the various elements of the nutritional composition considerably influences the values found. For this reason a few standard sources were used wherever possible and the sources are mentioned in the text. These sources are: McCance & Widdowson’s The composition of foods; the USDA Nutrient database for standard reference; FAO Food composition table for use in Africa.

Apart from nutrients, the properties include compounds with possible or proven medicinal value, toxins and other relevant chemical compounds.

Description

A morphological characterization of the species is given. The description is in ‘telegram’ style and uses botanical terms. Providing a description for the general public is difficult as more generally understood terms often lack the accuracy required in a botanical description. A line drawing is added for all major and some lesser-known species to complement and visualize the description.

Management

Descriptions of husbandry methods including fertilizer application, irrigation and pest and disease control measures are given under ‘Management’ and under ‘Diseases and pests’. These reflect actual practices or generalized recommendations, opting for a broad overview but without detailed recommendations adapted to the widely varying local conditions encountered by farmers. Recommendations on chemical control of pests and diseases are merely indicative and local regulations should be given precedence. PROTA will participate in the preparation of derived materials for extension and education, for which the texts in this volume provide a basis, but to which specific local information will be added.

Genetic resources

The genetic diversity of many plant species in Africa is eroding, sometimes at an alarming rate, as a consequence of habitat destruction and overexploitation. The replacement of landraces of cultivated species by modern cultivars marketed by seed companies is another cause of genetic erosion. Reviews are given of possible threats for plant species and of the diversity within species. Information on ex-situ germplasm collections is mostly extracted from publications of the International Plant Genetic Resources Institute.

Breeding

In comparison with other parts of the world, little breeding work aiming specifically at conditions in Africa has been done and few seed companies offer seed of locally adapted cultivars. Large differences exist in the occurrence of landraces, and local production of exotic vegetables, e.g. tomato, carrot and onion, is more based on farm-saved seed in West Africa than in East Africa, where the seed is more often imported. However, French bean seed in West Africa is mostly imported, while in East Africa it is locally produced. Seed of white headed cabbage is almost exclusively imported in all countries. Seed companies offering locally adapted cultivars, either bred in situ or elsewhere in the tropics for comparable conditions, are mentioned. Citing a cultivar does not imply a recommendation.

References

The main objective of the list of references given is to guide readers to additional information; it is not intended to be complete or exhaustive. Authors and editors have selected major and other references; major references are limited to 10 references (5 for minor species), the number of other references is limited to 20 (10 for minor species). The references listed include those used in writing the account. Where data available on the Internet have been used, the website and date are also cited.

Editors

• G.J.H. Grubben, Boeckweijdt Consult, Prins Hendriklaan 24, 1401 AT Bussum, Netherlands
• O.A. Denton, National Horticultural Research Institute, P.M.B. 5432, Idi-Ishin, Ibadan, Nigeria

Associate editors

• C.-M. Messiaen, Bat. B 3, Résidence La Guirlande, 75, rue de Fontcarrade, 34070 Montpellier, France
• R.R. Schippers, De Boeier 7, 3742 GD Baarn, Netherlands

General editors

• R.H.M.J. Lemmens, PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands
• L.P.A. Oyen, PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands

Photo editor

• E. Boer, PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands