The pencil cactus is a large plant native to Africa and India. The plant is ideal for sunny warm spots indoors or greenhouse growing. Care of pencil cactus is minimal. Euphorbia tirucalli, or pencil cactus, is a tropical plant that may become 30 feet (9 m.) tall in habitat. The stems are slender and slightly toothed with no obvious foliage. The branches are the diameter of a pencil, which give rise to the name. The new growth on the end may be tinged pink and have tiny leaves which disappear as the branch matures.