Solanum melongena

Solanum melongena is a cultivated to semi-wild herb with large shallowly-lobed leaves with rounded lobes and large white or purple flowers, grown for its large edible white, yellow, or purple fruits. Modern understanding of eggplant origins has its origins in work done by members of Richard Lester’s group at the University of Birmingham (Lester & Hasan 1991). In this scenario ancestors of tropical African S. campylacanthum (groups A and B) gave rise to ancestors of southern African S. lichtensteinii (group D) and northern African S. incanum s.s. (group C). Solanum incanum s.s. is then proposed to have dispersed into Arabia and Asia, possibly aided by man because of the value of its berries for tanning hides (Bitter 1923). The eggplant was likely domesticated in Indo-China from the wild progenitor S. insanum, giving rise to the great variety of cultivars found there, including the more “primitive” prickly S. melongena (group G) and eventually the commercial cultivars (group H). Lester also hypothesized that escape into the wild could have led to the formation of small prickly weeds S. insanum L. (sometimes called S. undatum and S. cumingii, groups E and F, here recognized as S. insanum, see also Knapp et al. 2013). The relationships of the African eggplant relatives are supported by results from molecular phylogenetics (Weese & Bohs 2010; Vorontsova et al. 2013). Early domesticates recorded from 300 BC in India and from 59 BC in China are likely to have been small, globular, and bitter (Wang et al. 2008); the elongated fruit type is not recorded until the 16th century (Daunay & Janick 2007). For an account of cultivation history and early illustrations see Daunay & Janick (2007).

The characters distinguishing S. melongena from the rest of the eggplant clade are mainly those directly associated with cultivation: larger fruit, altered fruit shape and color, and lack of prickles. Like the fruit crop cultivars of S. aethiopicum, it often exhibits fasciation in the flowers with an increase in the number of flower parts up to 8 and straight thick styles not exserted further than 2 mm beyond the anthers. Increased anthocyanin in the stems, leaves and corollas are likely an accidental by-product of selection for fewer prickles, as the loci responsible are located near each other (Doganlar et al. 2002).

Solanum melongena can be distinguished from S. incanum by its lack of prickles or rarely straight prickles (versus curved prickles, rarely straight prickles in S. incanum) and moderate pubescence making the plant green-brown or reddish as herbarium specimens (versus dense pubescence making the plant pale yellow in S. incanum).

Solanum melongena can be distinguished from S. cerasiferum by its obtuse to cordate leaf bases (versus attenuate leaf bases in S. cerasiferum) and rounded leaf lobes (versus rounded to acute leaf lobes in S. cerasiferum). Solanum melongena can be distinguished from S. aethiopicum by its mauve to purple corolla 2.5-5 cm wide and lobed for 1/4-1/3 of the way to the base (versus white corolla 0.8-1.8 cm wide and lobed for ca. 2/3 of the way to the base in S. aethiopicum). Solanum melongena can be distinguished from S. insanum by its lack of prickles or acicular prickles never more than 0.5 mm wide, and restricted to calyces and sometimes also stems and petioles. This division is to a certain extent artificial, but we prefer to maintain the cultivated and wild forms as separate species (see also Peralta et al. 2008 for a similar situation in the cultivated tomato, S. lycopersicum L., and its wild progenitor, S. pimpinellifolium L.); cultivated plants are in a completely different evolutionary environment with different selection pressures than their wild progenitors.