Solanaceae is a family of flowering plants that includes a number of important agricultural crops. Many species are toxic plants. The name of the family comes from the Latin Solanum "the nightshade plant", but the further etymology of that word is unclear. Most likely, the name comes from the perceived resemblance that some of the flowers bear to the sun and its rays, and in fact a species of Solanum (Solanum nigrum) is known as the "sunberry". Alternatively, the name has been suggested to originate from the Latin verb solari, meaning "to soothe". This presumably refers to soothing pharmacological properties of some of the psychoactive species of the family.

The family is also informally known as the nightshade or potato family. The family includes Datura, Mandragora (mandrake), Atropa belladonna (deadly nightshade), Lycium barbarum (wolfberry), Physalis philadelphica (tomatillo) , Physalis peruviana (Cape gooseberry flower), Capsicum (chili pepper, bell pepper), Solanum (potato, tomato, eggplant), Nicotiana (tobacco), and Petunia. With the exception of tobacco (Nicotianoideae) and petunia (Petunioideae), most of the economically important genera are contained in the subfamily Solanoideae.

Many members of the Solanaceae family are used by humans, and are important sources of food, spice and medicine. However, Solanaceae species are often rich in alkaloids whose toxicity to humans and animals ranges from mildly irritating to fatal in small quantities.

Description

Plants are herbs, shrubs, trees, or sometimes vines. The flowers are usually actinomorphic. Flower shapes are typically rotate (radiately spreading in one plane with a short tube) or tubular (elongated cylindrical tube), with four or five petals that are usually fused. Leaves are alternate. The fruit has axile placentation and is a berry as in the case of the tomato or wolfberry, or a dehiscent capsule as in Datura. The seeds are usually round and flat, about 2–4 millimetres (0.079–0.16 in) in diameter. The stamens are epipetalous and are typically present in multiples of four or five, most commonly four or eight. The ovary is superior.^[2]

Genetics

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Most Solanaceae members have 12 chromosomes^[3], a number that has increased due to polyploidy. Wild potatoes, of which there are approximately 200, are predominantly diploid (2 * 12 = 24 chromosomes), but triploid (3 * 12 =36 chromosomes), tetraploid (4 * 12 = 48 chromosomes), pentaploid (5 * 12 = 60) and even hexaploid (6 * 12 = 72 chromosome) species or populations exist. The cultivated species Solanum tuberosum has 4 * 12 = 48 chromosomes. Some capsicum species have 2 * 12 = 24 chromosomes, while others have 26 chromosomes.

Alkaloids

Solanaceae is known for having a diverse range of alkaloids. As far as humans are concerned, these alkaloids can be desirable, toxic, or both.

One of the most important groups of these compounds is called the tropane alkaloids. The term "tropane" comes from a genus in which they are found, Atropa (the belladonna genus). Atropa is named after the Greek Fate, Atropos, who cut the thread of life. This nomenclature reflects its toxicity and lethality.

Tropane alkaloids are also found in the Datura, Mandragora, and Brugmansia genera, as well as many others in the Solanaceae family.^[4] Chemically, the molecules of these compounds have a characteristic bicyclic structure and include atropine, scopolamine, and hyoscyamine. Pharmacologically, they are the most powerful known anticholinergics in existence, meaning they inhibit the neurological signals transmitted by the endogenous neurotransmitter, acetylcholine. Symptoms of overdose may include dry mouth, dilated pupils, ataxia, urinary retention, hallucinations, convulsions, coma, and death.

Despite the extreme toxicity of the tropanes, they are useful drugs when administered in extremely small dosages. They can reverse cholinergic poisoning, which can be caused by overexposure to pesticides and chemical warfare agents such as sarin and VX. More commonly, they can halt many types of allergic reactions. Atropine, a commonly used ophthalmological agent, dilates the pupils and thus facilitates examination of the interior of the eye. Scopolamine is used as an antiemetic against motion sickness or for people receiving chemotherapy. Atropine has a stimulant effect on the central nervous system and heart, whereas scopolamine has a sedative effect.

An infamous alkaloid derived from Solanaceae is nicotine. Like the tropanes, its pharmacology acts on cholinergic neurons, but with the opposite effect (it is an agonist as opposed to an antagonist). It has a higher specificity for nicotinic acetylcholine receptors than other ACh proteins. Nicotine occurs naturally in the Nicotiana or tobacco genus.

Another class of toxic substances found in this family are the glycoalkaloids, for example solanine which has occasionally been responsible for poisonings in people who ate berries from species such as Solanum nigrum or Solanum dulcamara, or green potatoes.^[5][6]

The chemical in chili peppers responsible for the burning sensation is capsaicin. Capsaicin affects only mammals, not birds. Pepper seeds can always survive the digestive tract of birds; their fruit becomes brightly colored once its seeds are mature enough to germinate, thereby attracting the attention of birds who then distribute the seeds. Capsaicin extract is used to make pepper spray, a useful deterrent against aggressive mammals.

Selected genera

See also

• List of plants poisonous to equines

References

This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (August 2008)

Further reading

• Hawkes, J. G., Lester, R. N., Skelding, A. D. (1979). The biology and taxonomy of the Solanaceae. Academic Press, London. ISBN 0-12-333150-1. 
• D'Arcy, William G. (1986). Solanacea. Columbia University Press. ISBN 0-231-05780-6. 
• Radford, Albert E. (1986). Fundamentals of Plant Systematics. Harper & Row, Publishers, Inc.. ISBN 0-06-045305-2.