Solanaceae
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| Missing image Brugmansia_lg.jpg A flowering Brugmansia x insignis from the US Botanic Garden | ||||||||||
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Acnistus
Families of Flowering Plants (http://biodiversity.uno.edu/delta/angio/www/solanace.htm) |
The nightshades (Family Solanaceae) are a family of dicots, many of which are edible, while others are considered poisonous. The etymology of the family is unclear; it has been suggested it originates from the Latin word "solari," meaning soothing. This would presumably refer to alleged soothing pharmacological properties of some of the psychoactive species found in the family. It is more likely, however, that the name comes from the perceived resemblance that some of the flowers bear to the sun and its rays. The taxon is also sometimes informally referred to as the potato family. The family includes the datura or Jimson weed, eggplant, mandrake, deadly nightshade or belladonna, capsicum (paprika, chilli pepper), potato, tobacco, tomato, and petunia. The Solanaceae family is characteristically ethnobotanical, that is, extensively utilized by humans. It is an important source of food, spice, and medicine. However, Solanaceae species are often rich in alkaloidal glucosides that can range in their toxicity to humans and animals from mildly irritating to fatal in small quantities.
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Synonyms and common names
Nightshade is any member of the genus Solanum, of which the potato (S. tuberosum) and eggplant (S. melongena and S. esculentum) are part. "Shade" does not refer to the blockage of light, but actually descends from the German word "schade," meaning destruction or damage (attributed to the toxic/fatal effects characteristic of many Solanaceae species). The name Nightshade, or informally, potato, is also extended to the family Solanaceae.
Botanical Characteristics
Flowers are typically conical or funnelform with five petals, usually fused. The leaves are alternate with a clammy surface. Solanaceous plants produce a fruit that is either a berry, as in the case of the tomato, or a dehiscent (breaks open upon drying, or dehiscing, releasing the seeds) capsule as in the case of Datura and chili peppers. The seeds are usually round and flat, being 2-4 millimeters in diameter. Stamens are usually present in multiples of four (most commonly four or eight). Ovaries are inferior. The hypogynus gynoecium is a syncarp located obliquely in relation to the median.
Alkaloids
The Solanaceae are known for possessing a diverse range of alkaloidal glucosides, or simply alkaloids. These nitrogenous chemicals are thought to have evolved for the purpose of discouraging animals from herbivory. For humans these alkaloids can sometimes be desirable, toxic, or both.
One of the best known groups of these compounds are called the tropane alkaloids. The name comes from a genus in which they are found, Atropa or belladonna. The name comes from the Greek fate, Atropos, who cut the thread of life. Clearly, these compounds have long been known to be highly toxic. Tropane alkaloids are also found in the Datura, Mandragora, and Brugmansia genera, as well as many others. The compounds characteristically have a bicyclic structure and include atropine, scopolamine, and hyoscamine. Pharmacologically, they are the most powerful known anticholinergics, meaning they inhibit the neurological signals transmitted by the endogenous neurotransmitter, acetyl choline. Symptoms of poisoning include dry-mouth, hallucinations, dilated pupils, ataxia, urinary retention, convulsions, coma, and death. Despite the toxicity of the tropanes, they are important drugs when administered in appropriate (and 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. Scopolamine is a commonly used opthamalic agent for dilating the pupils to facilitate exploration of the eye. They can also be used as antiemetics in people prone to motion sickness or receiving chemotherapy. Atropine has a stimulant effect on the central nervous system whereas scopolamine has a sedative effect. It should be noted that cocaine is also considered a tropane alkaloid due to its structural resemblance to the aforementioned compounds, but its pharmacology is radically different and it does not occur in the Solanaceae family.
The most famous and controversial alkaloid from this family 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). Its effects are well known. Nicotine occurs naturally in the Nicotiana or Tobacco genus.
Capsaicin is structurally unrelated to nicotine or the tropanes, and is found in the Capsicum genus, which includes Tabasco peppers and habaneros. The compound is not toxic to animals. However, it stimulates specific pain receptors, those which sense heat, in the oral mucosa as well as many other epithelial tissues, causing a sensation of burning. It is used in high concentration as a deterrent in pepper sprays, and sought after for many culinary dishes for its "spiciness." It is thought that the reason one would deliberately induce pain while eating is the rewarding release of endorphins it has been shown to induce.
Nutritional importance
The most important species of this family for the global diet is the potato or Solanum tuberosum. Although this plant is generally considered toxic, swollen parts of the roots known as tubers generally possess no toxicity, but rather a copious store of carbohydrates that both the plant and humans can use to obtain energy. However, the tubers may become toxic if allowed to sprout. Green areas on a potato indicate new growth, which may indicate the presence of solanine, a glycoalkaloid compound with antibiotic properties that can be poisonous in sufficient quantities. In many genera, the fruits are the desirable item:Tomatoes, eggplants, and peppers fall into this category.
Solanaceae Network - pictures of plants (http://www.solanaceae.net/index.php)
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