 Lettuce is very easy to grow , and as such has been a significant source of sales for many seed companies . Tracing the history of many varieties is complicated by the practice of many companies , particularly in the US , of changing a variety 's name from year to year . This was done for several reasons , the most prominent being to boost sales by promoting a " new " variety or to prevent customers from knowing that the variety had been developed by a competing seed company . Documentation from the late 19th century shows between 65 and 140 distinct varieties of lettuce , depending on the amount of variation allowed between types – a distinct difference from the 1 @,@ 100 named lettuce varieties on the market at the time . Names also often changed significantly from country to country . Although most lettuce grown today is used as a vegetable , a minor amount is used in the production of tobacco @-@ free cigarettes ; however , domestic lettuce 's wild relatives produce a leaf that visually more closely resembles tobacco . 
