7. Solanum L. (nightshade)

Plants in our species annual or perennial herbs (the stems climbing, twining, and often woody toward the base in S. dulcamara), sometimes with rhizomes or tubers, sometimes armed with prickles. Stems variously erect to loosely ascending or spreading (climbing in S. dulcamara), unbranched or more commonly branched, glabrous or hairy. Leaf blades simple or less commonly 1 or 2 times pinnately deeply lobed to compound, glabrous or variously hairy. Inflorescences mostly axillary or lateral (positioned opposite the leaves), clusters, racemes, or small panicles, rarely of solitary flowers. Flowers variously ascending, spreading, or nodding. Calyces fused to the midpoint or less, bell-shaped to saucer-shaped, rounded to truncate at the base, lacking basal auricles, persistent intact at fruiting (the tips of the lobes sometimes breaking off with age), not or only slightly enlarged, or, if enlarged and closely surrounding all or part of the fruit, then not balloonlike or papery, not angled. Corollas saucer-shaped to broadly bell-shaped, sometimes with the lobes more or less reflexed, usually appearing pleated in bud, white to purple or blue, less commonly cream-colored or yellow. Stamens with short filaments, the anthers fused or merely positioned into a ring, dehiscent longitudinally (in S. lycopersicum) or by terminal pores (these sometimes narrow and slitted), light yellow to orangish yellow, occasionally reddish- or purplish-tinged. Ovary 2(–4)-locular, the style often protruding through the center of the anther ring. Fruits berries (burlike in S. rostratum), more or less juicy, variously shaped, 2(–4)-locular, variously green, yellow, orange, or red, occasionally with lighter mottling, with several to numerous seeds, sometimes with irregularly globose groups of hard granules (composed of stony cells) among the seeds. Seeds various, lacking wings. About 1,500 species, nearly worldwide.

Solanum is the largest genus in the family and is particularly diverse in neotropical regions, where many of the species are shrubs or small trees. It is economically very important, including such food plants as tomatoes, eggplants, and potatoes. Some of the species in the United States are important weeds of crop fields and rangelands. As with most other members of the Solanaceae, plants of Solanum species (other than the edible portions of particular species) contain alkaloids that are poisonous to humans and livestock. The species with prickly stems and leaves also can sometimes cause injuries to the mouthparts and feet of livestock. For a wealth of information on the genus, users of the internet are directed to the excellent Solanaceae Source website (http://www.nhm.ac.uk/research-curation/research/projects/solanaceaesource/).

The unusual morphology of the stamens is an adaptation to buzz pollination (also known as sonication) by certain bees (Buchmann, 1983). This adaptation has evolved independantly in some members of the Solanaceae and in several other plant families, for example, in the shooting star group of Primula (Primulaceae) and in some members of the Ericaceae. A rapid contraction of the indirect flight muscles of the bee causes the anther to vibrate (sonicate), which causes the pollen to be expelled through the apical openings where it can be collected easily by the bee.