Most of Norfolk’s arable fields are filled with a small and predictable set of crops: wheat, barley, sugar beet, potatoes and oilseed rape. Sometimes, however, a surprise awaits for the observant.
A few weeks ago my friend Sarah met up with some other friends for a walk at Stonebridge in Norfolk and noticed a strange crop growing in a large field by the side of the A1075. The plants had flowers like potatoes but the leaves were spiny and divided. She asked me if I knew what it was, and sent me a couple of photographs.
The mystery crop turned out to be Sticky Nightshade, Solanum sisymbriifolium. Around the same time I found the plant growing in Cambridge Botanic Garden and then last week Sarah drove me out to Stonebridge so I could take my own photographs.
Sticky Nightshade, Solanum sisymbriifolium is a native of South America: Brazil, Argentina, Uruguay and Paraguay. It is a member of the family Solanaceae and its white flowers (with a hint of purple or blue) are very similar to those of the potato (also a Solanum). Later in life, fruits form, which look like small, bright red tomatoes. These form inside a husk, like the tomatillo, Physalis philadelphica. The plant is an annual herb or small shrub and grows about a metre tall. Its stems and leaves are very prickly, with orange-brown spines. The leaves are sticky, and the fruits are slightly sticky too. The English name Sticky Nightshade is very appropriate.
Sticky Nightshade’s leaves are divided and the name sisymbriifolium refers to their resemblance to the leaves of the mustard genus Sisymbrium. (The commonest British species of Sisymbrium is Hedge Mustard, Sisymbrium officinale.)
Other names for the plant include Fire-and-Ice plant, Litchi Tomato, Morelle de Balbis and Dense-Thorned Bitter Apple. (Morelle de Balbis is named after Giambattista Balbis, an Italian botanist from Turin.) The Global Invasive Species Database lists synonyms for the scientific name and names in various languages. The Rob’s Plants website has some great photos of the plant.
Potato Cyst Nematodes (PCN) are a damaging pest of potatoes, causing damage to the roots and reducing yields, often with no symptoms above ground, although in severe attacks plants can be stunted and have yellow leaves (chlorosis). Crop rotation and the use of partially resistant potato varieties can help to restrict the damage. (Read more on the DEFRA and Potato Council websites.)
Sticky Nightshade is grown as a trap crop for potato cyst nematodes. If Solanum sisymbriifolium is planted in a field infested with PCN, the nematode eggs hatch and the nematodes try to feed on the roots, but these are poisonous to the nematodes, which die. The nematode lifecycle is broken and an ordinary potato crop can be planted in the field. In the UK the plant is marketed as ‘DeCyst’ or ‘Foil-sis’ (reference).
(As an aside, research is also being carried out on the use of brassicas with high levels of glucosinolates to control potato cyst nematodes. When these crops, such as Indian mustard, are ploughed into the soil the glucosinolates break down into isothiocyanates, which are toxic to potato cyst nematodes.)
Solanum sisymbriifolium contains the poisonous alkaloid solasodine. This can be used as a precursor to build other chemicals, such as steroidal compounds used in contraceptive pills. It may also be useful as an anticonvulsant.
Regardless of its various uses, there is no denying that Sticky Nightshade is a very pretty and fascinating plant in its own right.