Cactus or Cacti show a wide variety of growth habits, which are difficult to divide into clear, simple categories. They can be tree-like (arborescent), meaning they typically have a single more-or-less woody trunk topped by several to many branches. In the genus Pereskia, the branches are covered with leaves, so the species of this genus may not be recognized as cacti. In most other cacti, the branches are more typically cactus-like, bare of leaves and bark, and covered with spines, as in Pachycereus pringlei or the larger opuntias. Some cacti may become tree-sized but without branches, such as larger specimens of Echinocactus platyacanthus. Cacti may also be described as shrubby, with several stems coming from the ground or from branches very low down, such as in Stenocereus thurberi.