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Solanum tuberosum

Nightshade Family [Solanaceae]

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15th June 2009, Arable Fields, Martin Mere, Lancs. Photo: © RWD
A crop of purple-flowered potatoes growing in a field. Variety unknown.

15th June 2009, Arable Fields, Martin Mere, Lancs. Photo: © RWD
A crop of white-flowered potatoes growing in a field. Variety unknown.

15th June 2009, Arable Fields, Martin Mere, Lancs. Photo: © RWD
A lone young plant. Many more leaves than flowers.

15th June 2009, Arable Fields, Martin Mere, Lancs. Photo: © RWD
About eight or so flowering stems sprout from the tallest shoots, each one bearing a five-pointed flower with a central column of five yellow anthers. Flowering stems are hairy.

15th June 2009, Arable Fields, Martin Mere, Lancs. Photo: © RWD
Leaves in opposite pairs along the length of a stem.

15th June 2009, Arable Fields, Martin Mere, Lancs. Photo: © RWD
the petals are fused into one which has five shallow points. The sepals behind are also fused, but have five longer points. Hairy stems.

15th June 2009, Arable Fields, Martin Mere, Lancs. Photo: © RWD
This aberrant specimen appears to have six fused petals and six yellow anthers. Flowers tend to droop downwards.

15th June 2009, Arable Fields, Martin Mere, Lancs. Photo: © RWD
The petals have hairs on the periphery at the points.

15th June 2009, Arable Fields, Martin Mere, Lancs. Photo: © RWD
Lanceolate leaves in opposite pairs, some terminal leaflets much larger than the rest. Conspicuous veins sunken on rippled surface.

13th Sept 2012, home, kitchen. Photo: © RWD
Here's one I made earlier, a potato left to sprout for 2 months. The solanines are most concentrated in the sprouting parts. This specimen is an extreme example and should be thrown away in its entirety and not eaten, even if the sprouting parts are surgically removed with a kitchen knife. It could, however, be planted instead where it will grow many more tubers. This specimen was left on the kitchen table exposed to light and warmth; constant evaporation seems to have limited the length of the sprouting shoots in favour of number. If left to sprout in a cool dark fridge, the sprouting shoots are much fewer in number but much longer in length.

Not to be confused with : Duck-Potato [a plant with similar name but of differing Family]

Some similarities to : Tomato but that has yellow petalled flowers which are narrower and cut deeper than those of Pototo.

The flower has superficial resemblance to those of: Aqualegia (Columbine which are also purple, droop downwards, and have five pointed petals, but otherwise the plant is totally different.

Uniquely identifiable characteristics

Distinguishing Feature :

Potatoes are grown as the main staple diet for folk in the UK. According to the BBC Radio program 'Farming Today', potatoes are the third most important staple crop in the World (although it was not made clear if this is by nutritional value, by weight of crop, or by area planted or whether by some other unknown criteria). Locally it is grown in Ireland, Lancashire and Cheshire as well as other areas such as Lincolnshire. The flowers have five petals and five yellow stamens that generally congregate as one to protrude rudely from the centre of the flower. The petals are either white or pale purple, but other varieties exist with pink, red and blue petals. There are two basic types that are commonly cultivated; those with pinkish skins, and those with white skins. The potatoes with white skins tend to have white petalled flowers, whereas those with pinkish skins tend to have flowers with coloured petals. There are many other types of Potato, including Purple Potato, which seems to be extinct in the UK. When left to grow without being harvested, the flowers will produce small green poisonous tomato-like fruits which contain up to 300 seeds. Potatoes can be grown from these seeds, or vegetatively by re-planting sprouting tubers. Paradoxically, so-called 'seed-potatoes' are tubers intended to be planted for vegetative propagation!

Just recently a potato has been bred with a deep beetroot or purple coloured tuber called 'Purple Majesty', which is sold by a well known UK supermarket. The deep purple coloration is throughout the bulk of the tuber, not just on the surface. There are about 5000 other varieties of potato in the World, many non-white.

The potato has been bred so as to minimise the poisonous alkaloids within the tubers called collectively Solanines, but this is not necessarily so for any other part of the plant such as the leaves, stems or flowers or berries, which still tend to be deadly poisonous. (No one eats potato leaves as salad!).

However, the edible tubers (called 'potatoes') do contain residual amounts of solanines, with a particularly high concentration in and around any sprouting parts, which is why any sprouting shoots should always be removed before cooking. If the tubers, once lifted from the ground, are exposed to light or sunlight, they will turn green on the exposed side. The green is just chlorophyll, but wherever any green parts form, the solanine concentration around that area soars very high, making them particularly poisonous. Any green parts of potatoes should be removed before cooking. Although some insubstantial proportion of the solanine content is destroyed on cooking, much still remains. Eating green potatoes kills! Potatoes are, after all, a member of the Nightshade Family, which includes Deadly Nightshade.

The potato plant produces tubers on its extensive roots as an energy store for the coming winter months when photosynthesis is at a minimum. The tubers are almost wholly carbohydrates; starch, which is not a single compound, but a mixture of polysaccharides; polymerised amylose sugar units (glycosides).

Potato is one of the few plants capable of converting the inorganic chloride ion (as found, for example, in common salt, NaCl) into organic chlorine. Other plants capable of this are Yellow Star-Thistle, Common Valerian and many plants in the Pea Family (Fabaceae)). Potatoes can release small amounts of Methyl Chloride CH3Cl, gas (an organocloride) into the atmosphere after harvesting, providing it had access to a source of inorganic chloride, which most do. (These are quite separate from the organochlorine residues found in plants as a result of organochloride pesticides sprayed onto them). See Organochlorides in plants on the Chameleon page.


The glycoalkaloid poisons α-solanine and α-chaconine are to be found in the nightshade family of plants, the (Solanaceae), in particular in potatoes (Solanum tuberosum), tomatoes (Solanum lycopersicum or Lycopersicon esculentum), egg plant (aubergines) (Solanum melongena), Sweet and hot peppers (Capsicum species) Thorn-Apple (Datura stramonium), Apple-of-Peru (Nicandra physalodes), Black Nightshade (Solanum nigrum) and Bittersweet (Solanum dulcamara). It is present in small quantities throughout potato tubers, especially in the sprouting shoots, but a lot more is synthesized by the potato if the tuber is exposed to sunlight, where the exposed parts become green (with harmless chlorophyll). It is in and near the green parts where the highest concentration of solanine is to be found. Solanine is not rendered safe by boiling, much still remains, but deep frying at 170 Celsius does destroy most of the solanine. Normally, potatoes contain poisonous solanines at concentrations between 20mg and 150mg per kilogram of raw potato, but when turned green on exposure to sunlight may contain as much as 1000mg/kg, mostly just under the skin (the shoots contain even higher amounts). Solanine adds an un-pleasant bitterness to the flavour of potatoes when its concentration exceeds 200mg/kg, so potato poisoning is now rare, especially as cooks are now more aware of the dangers of greening or sprouting potatoes.

Solanine has, amongst many other effects, a choline esterase inhibitor function and thus affects the central nervous system. The symptoms of solanine poisoning are nausea, vomiting, diarrhoea, stomach cramps, burning of the throat, heart arrhythmia, dizziness, and in severe cases hallucinations, loss of feeling, paralysis, jaundice, hypothermia and death. It causes apoptosis in cells; the cells commit suicide. Ingested concentrations of solanines of between 2mg and 5mg per kilogram of body weight will cause severe poisoning, possibly fatal.


Demissidine, as a glycoalkaloid with glycosides attached [which are not shown here], is found in significant concentrations in the skins of un-ripe potatoes. It is reported to inhibit the enzyme cholinesterase and is also a suspected teratogenic substance, inducing gross abnormalities and birth defects in newborns (such as two heads). It modifies DNA. It has been shown to have anti-bacterial properties, such as activity against Staphylococcus aureus, the bacteria responsible for MRSA. In comparison to the solanines above, Demissidine lacks the double bond in the steroid entity, and also a methyl group on the piperidine group (top right).


Calystegines are poly-hydroxylated nortropane alkaloids, derived from Tropane but without the methyl group on the nitrogen atom. These two are found in potatoes, Tomatoes, Sweet and Chili Peppers, Eggplants, Sweet Potatoes, Mulberries and Cabbage and are potent glycosidase inhibitors. They were first reported in plants of the Bindweed Family (Convolulaceae) but are most ubiquitous in the Nightshade Family (Solanaceae). The major proportion of these alkaloids are synthesized within the roots, and the largest increase in production was observed in tubers that have suppressed sucrose synthase activity. Increases in calystegines seems to be linked with sucrose availability.

Calystegines are not destroyed by cooking and are stable enough to be found in processed potato products such as dried mash potato. Storage of potato tubers at 5°C increases the 4-O-α-D-galactoside of Calystegine B2 and Calystegine A3.

The inhibition of mammalian β-glucosidase and α-galactoside activities raises the possibility of toxicity in humans when large quantities of these plants are consumed.

Other Calystegines are to be found within Apple-of-Peru, Danish Scurvygrass and other plants.

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Solanum tuberosum

Nightshade Family [Solanaceae]

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