American nightshade

Appearance

It grows up to 1–1.5 metres tall and is an annual or short-lived perennial. The leaves are alternate on the branch, and vary greatly in size, up to 10 centimetres long and 7 centimetres broad, with a 4-centimetre petiole and a coarsely wavy or toothed margin.

The flowers are about 1 cm diameter, white or occasionally light purple, with yellow stamens. The fruit is a shiny black berry 5–10 millimetres diameter, containing numerous small seeds.

It is one of the most widespread and morphologically variable species belonging to the section ''Solanum''. It can be confused with other black nightshade species in the ''Solanum nigrum'' complex.

Distribution

The plant is widely naturalised around the Tropical Pacific and Indian Oceans, including Hawaiʻi, Indochina, Madagascar and Africa, possibly via anthropogenic introduction in these locales.

Food

The ripe fruit is cooked into jams and preserves, or eaten raw. In Africa, South America, New Guinea and Oceania the young green shoots of ''Solanum americanum'' are cooked and eaten as greens, after boiling in water. The cooking water used for boiling the leaves is discarded as it contains the soluble alkaloids. In Kenya, Cameroon and Papua New Guinea the leaves are sold as a leaf vegetable in the markets. The leaves are used in a West Indian stew, and it is known as branched Kalaloo. In Mauritus it is cultivated and eaten as a pot-herb and used in bouillon. Experts warn that care should be taken since numerous toxins are reported with levels varying with local conditions and varieties.

Defense

Research indicates the presence of toxic glycoalkaloids and there are warnings to be careful on the use of ''S.americanum'' as herbal medicine and food. The green fruit is particularly poisonous and eating unripe berries has caused the death of children. Ripe berries and foliage may also cause poisoning. This is via high levels of the glycoalkaloids, solanine and solamargine,. Other toxins present in the plant include chaconine, solasonine, solanigrine, gitogenin and traces of saponins, as well as the tropane alkaloids scopolamine , atropine and hyoscyamine.

Significant amounts of solasodine have been found in the green berries. The ripe fruit also contains 0.3-0.45% solasonine, and acetylcholine, and has a cholinesterase-inhibiting effect on human plasma. In Transkei, rural people have a high incidence of esophageal cancer thought to be a result of using ''S.americanum'' as a food. Livestock can also be poisoned by high nitrate levels in the leaves.

Toxicity varies widely depending on the genetic strain and the location conditions, like soil and rainfall. Poisonous plant experts advise: "...unless you are certain that the berries are from an edible strain, leave them alone."

Uses

Extracts from ''S.americanum'' were found to have selective antiviral activity against the herpes simplex type-1 virus .

Methanol extracts of ''S.americanum'' have high antimicrobial activity against ''Escherichia coli'', ''Pseudomonas aeruginosa'', ''Staphylococcus aureus'' and ''Aspergillus niger''. Water based extracts had no antibacterial activity.