The Trinity lettuce is a hybrid of three differently coloured varieties - lollo biondo, lollo rosso and red oak leaf.
The lettuce, grown in a 14-acre glasshouse in Cranleigh, Surrey, retails at 99p. It is stocked in 360 stores with weekly volumes at 5,600 head.
Meanwhile, Sainsbury has begun to sell fair trade avocados in 150 stores.
The avocados, all grown on a single 6,000ha farm in South Africa, are a green skin variety called Feurte, said to have a light texture and taste.
A fairtrade two-pack retails at £1.89. JS’s non-fairtrade medium avocados sell for 79p each.