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Diversity of African vegetable Solanum Species
lisations there. They also spread westwards through the then green savanna habitats
of the Sahara and Sudan 5,000 or more years ago, thus developing and culminating
in the great sub-Saharan African empires of Ghana, Kanem-Bornu, Mali and Songhay
in the 9th to 16th centuries (DAVIDSON 1972). As it spread, new grains indigenous
to Africa were domesticated and integrated into this agricultural system, and likewise
many new vegetables were added. How much indigenous agriculture had been developed
previously in Africa is very uncertain, especially for root crops such as yams
and other vegetables in the hot and humid areas where no archaeological remains
survive (HARLAN et al. 1976, HAWKES 1983).
For most of Africa, crops have been grown traditionally in mixed cultivation in gardens
or in small fields, the women farmers carefully maintaining their own genetic
resources from one season to the next (LESTER et al. 1990). This has produced land
races or primitive cultivars adapted to local conditions and preferences, and with
great diversity across Africa. European taxonomists, unaware of domestication processes,
have distinguished these as very many different species. In the case of Solanum,
these reduce to just four cultigens, namely S. scabrum Mill., S. melongena L.,
S. macrocarpon L. and S. aethiopicum L., together with their related wild species.
These are very distinct taxa, and although hybrids between S. melongena, S. macrocarpon
and S. aethiopicum are possible, they have low fertility (DAUNAY et al. 1991).
These three species are the brinjal, gboma and scarlet eggplants, respectively
(LESTER 1986). Here, as elsewhere, crossability is not congruent with either phenetic
or molecular similarities. S. melongena crosses more easily with S. aethiopicum yet it
is more similar to S. macrocarpon in many morphological characters. Likewise S.
melongena crosses easily with S. cerasiferum Dunal and with S. sessilistellatum Bitter
to produce fertile F1 hybrids (DAUNAY et al. 1998), yet it is distant from them according
to AFLP analyses of DNA. In this treatment we use the morphological species
concept (based on phenetic discontinuities), as applied in the new “Mansfeld’s
Encyclopedia” (LESTER and HAWKES 2001), which is the most useful for herbarium
taxonomists, rather than the biological species concept (based on reproductive isolation),
which may be more useful for plant breeders. The present treatment has to be
brief, but for more extensive treatments of this subject, we recommend the publications
of FAO (1988), DAUNAY et al. (2001a), SCHIPPERS (2000) and LESTER and
HAWKES (2001), which also treats potatoes and other Solanum crops introduced into
Africa from South America.
The four African vegetable Solanum species
1. Solanum scabrum Mill., etc. – Black Nightshades
Solanum nigrum L., the black nightshade, type species of Solanum L. subgenus Solanum
section Solanum, is a well known Eurasian weed, but its name is often misap-
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