western lettuce (also known as head lettuce and round lettuce) is a 1-or 2-year-old herbaceous plant of the genus Lettuce in Compositae, namely Lactuca sativa Linn or Lactuca sativa var. capitata L.. It can grow to .25 to .8 meters high, with hollow stems and milk. Most of the leaves are oblate, ranging from the typical long oval shape to the needle shape to the linear shape.