Types of cylinder leaf stems often regardless of section, such as general stems up to 2 meters, only one section has been upward, while belong to many kinds of flat section of the stem. Though you cannot return (opuntia brasilnsis) with flat stems, but the high lignification of main stem, flat form the stem just young branch. The cylindrical leaves no obvious kinds of opuntia, lignification main stem does not exist or is not obvious. Without those kinds of leaf photosynthetic due to its function mainly borne by the stem, so stem green under normal circumstances, the lignification.