The Pencil Cactus (Euphorbia tirucalli) — also commonly called milk bush due to its thick, white sap — is native to semi-arid tropical regions of Africa and India. In the wild, the Pencil Cactus can grow up to 30 feet tall and well over 6 feet indoors. This stem succulent is not a true cactus and photosynthesizes in its stems, not through the small leaves that appear at the end of its new growth (which are inconsequential to the plant’s health). The plants have slender, slightly toothed stems without any foliage growth. The name derives from the branches, which are about the diameter of a pencil. When new branches sprout, the end of the branch can be tinted slightly pink and tiny leaves may appear. These leaves will disappear once the branch matures. The pencil cactus needs high levels of light and moderately low moisture. It is an excellent houseplant and provides an interesting silhouette. The pencil cactus prefers bright, full sun. A sunny windowsill is a perfect location for this plant. It thrives with mild, warm temperatures, ranging from 65 F to 70 F. Temperatures around the plant should not drop below 50 F.