Solanum aethiopicum L.

Solanum aethiopicum is a widespread vegetable crop, and includes all cultivated forms derived from S. anguivi. Solanum aethiopicum can be identified and distinguished from S. anguivi by a combination of the following characters: annual herbaceous habit, usually a lack of stellate indumentum, smaller and more entire leaves, 1-2 flowers per inflorescence, short and thick pedicels, more than 5 perianth lobes, ovary enlarged even at anthesis, fruit over 1 cm in diameter and with more than two locules, not detaching easily from the pedicels, immature fruit striped and/or not green when immature, and seeds over 2.5 mm long. Cultivars used as leaf vegetables are easily recognizable by their thin membranous leaves and dark red-brown, almost black color when dried; these may have up to 10 small flowers. Cultivars used as fruit crops have larger, often ellipsoid or flattened berries and 1-2 flowers per inflorescence. Precise limits of this species are difficult to specify due to the wide variety of infrequently occurring characters. Stellate indumentum is one such infrequently occurring character. Approximately 90% S. aethiopicum specimens we have seen are glabrous but some cultivars used for fruit (Gilo group) exhibit a variety of stellate indumentum types. Prickly forms of S. aethiopicum have been recorded from European botanical gardens (Lester and Niakan 1986), but are not known in Africa.

Our knowledge of S. aethiopicum is largely due to the research program carried out by Richard Lester’s group: crossing studies by Pearce (1975) and Omidiji (1975, 1979, 1982) followed by numerical taxonomy, protein electrophoresis, and further crossing studies by Niakan (1980) and Lester and Niakan (1986) have demonstrated that S. aethiopicum, S. gilo, S. integrifolium, and S. olivare are all interfertile cultivated races of S. anguivi. The cultivars have been separated into four groups: the Gilo group (with stellate hairs and large, fleshy, variably shaped fruits), the Shum group (leaf vegetable with no stellate hairs of prickles, small fruits ca. 2 cm in diameter, common in Africa), the Kumba group (edible leaves that are almost glabrous as well as sweet flattened and deeply-grooved [fascinated] fruits), and the Aculeatum Group (prickly plants, flattened and deeply furrowed fruit, common in European botanical gardens but not known in Africa). Solanum anguivi was maintained as a distinct wild to semicultivated species due to its largely distinct morphology, lack of wild intermediates, and a probable selective pressure against new hybrids between S. aethiopicum and S. anguivi. For a comprehensive account of the taxonomic history and an overview of different cultivars see Lester and Niakan (1986). We follow the circumscription of Richard Lester and place the unarmed Solanum distichum and its synonyms in S. anguivi.

The epithet “scabrum” was used by several authors for S. aethiopicum; all of these names post-date S. scabrum Mill. (an unarmed hexaploid species of the Morelloid clade from Africa) and so are illegitimate. No specimens were cited in the description of Jacquin’s S. scabrum and we have lectotypified this name with the plate that accompanies the protologue. Solanum scabrum Zucc. is usually cited as having been published in J. J. Roemer’s Collecteana (1806, in December), but Zuccagni’s own preprint of the same material (Zuccagni 1806, earlier in the year) was distributed earlier so the place of publication of this name should be as cited as above (Roemer 1806; Stafleu and Cowan 1983).

In his 1813 thesis, Dunal based most of his infraspecific taxa in S. aethiopicum on pre-Linnaean descriptions and plates and seems not to have seen specimens to which he could refer these taxa; two of his varieties had polynomial names (“α Inerme; floribus albis; baccis rubris” and “β Inerme; floribus violaceis, baccis albis aut purpureis”) and are thus not validly published (see Names not validly published). Solanum aethiopicum var. aculeatum was described as “γ Aculeatum. An Species diversa?” (Dunal 1813), and several pre-Linnaean sources were cited. We have chosen the illustration in Morison’s Plantarum Historia Universalis Oxoniensis (1699) as the lectotype of this name as it is the only element cited by Dunal in the protologue that clearly illustrates a prickly plant.

Tenore (1855) attempted to make sense of the variation in S. aethiopicum and to treat the names coined by Dunal and others. He classified plants according to their fruit shape, lobulation and color, and provided illustrations of the taxa he recognized, including his new species described in 1850 (Tenore 1850). Unfortunately these lovely illustrations cannot be used as lectotypes, as they do not accompany the original protologues.

Pailleux and Bois (1890, 1892) described unusual vegetables cultivated in France. We have been unable to locate any specimens associated with their work, but the description of S. pierreanum was accompanied by a plate which we have seen in a tracing done by G. Bitter at GOET (see Vorontsova & Knapp 2010). We have lectotypified S. olivare using the illustration that accompanies the protologue, but have not seen the original description of S. pierreanum and so leave that name untypified. Both these names are probably better treated as horticultural variants.