Solanum sisymbriifolium is a plant that behaves as a weed and grows in disturbed areas, but is also found in undisturbed habitats at low densities.

It is a herb or small shrub, and can grow to about 1m tall.

The leaves are highly dissected and both sides are covered with sharp prickles. These are sometimes called spines or thorns, but technically they are prickles as they are outgrowths of the epidermis and not modified branches (spines).

In addition to the large prickles, Solanum sisymbriifolium has a covering of sticky hairs that are barely visible to the naked eye and give the plant its common name of viscid nightshade.

The flowers are large and white, sometimes tinged with purple, with 5 yellow anthers held in the centre.

Fruits are enclosed by the prickly calyx, until they are ripe, when they turn bright red and the calyx peels back to expose the fruit to birds and other animals which eat it and disperse the seeds.

Solanum sisymbriifolium was commonly grown in European botanical gardens as early as the eighteenth century - it was described by the French botanist Jean Baptiste Larmarck, who is better known for his theory of evolution that was based on the inheritance of acquired features.

For a long time this species was known in botanic gardens as Solanum balbisii, named for Giambattista Balbis, an Italian botanist from Turin, who originally called this species Solanum decurrens.

Both names were coined later than Solanum sisymbriifolium, and are considered synonyms. See Solanaceae Source for all the synonyms of Solanum sisymbriifolium

Lamarck described his plant from collections made near Buenos Aires, Argentina by Philibert Commerson, who was the French royal botanist and physician, and Louis Antoine de Bougainville’s assistant on his voyage around the world (1766–1768). Commerson’s assistant on the voyage was later found to be a woman, Jeanne Baré - she was the first woman to circumnavigate the globe.

Putting Solanum sisymbriifolium to use in disease control

Solanum sisymbriifolium is considered a problem weed in cattle pastures in southern South America, but in Europe it is being developed for use as a trap crop for potato cyst nematode (PCN). Also known as potato eel worm, this is a serious potato pest in the northern hemisphere.

PCN is a notifiable disease of potatoes in Scotland and has been the subject or recent EU directives for plant health.

It is used as a trap crop in the following way:

  • initially, a field of Solanum sisymbriifolium is planted in an infested potato growing area
  • the nematode eggs in the soil hatch out and try to feed on the poisonous roots of the trap crop Solanum sisymbriifolium
  • the nematodes die, leaving the soil nematode-free so another potato crop can be planted

In the UK the plant is marketed as DeCyst or Foil-sis. 

Greenvale - DecystThe weedy nature of Solanum sisymbriifolium means care must be taken to prevent spread, but its use is likely to reduce the need for chemical control of this devastating potato disease.