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Contrary to its name, the pencil cactus plant is not really a cactus. It is actually a member of the Euphorbiaceae family of succulents. The name pencil cactus came from the plant's characteristic thin spindles, which are used to store water to help the plant survive the arid desert climate. This plant goes by many names, including milk bush plant, petroleum plant, and Indian tree spurge. Cacti and succulents enthusiasts usually collect it for ornamental purposes.
The pencil cactus is a tropical plant that originated in parts of Asia and Africa. The plant was brought to western countries by collectors who prized the plant's unique appearance. When exposed to the sun, its normally green stems often gain a red orange color. This gave the plant the nickname "firestick."
Growing a pencil cactus often requires relatively little maintenance. Watering it a few times a month is enough for it to grow. The grower must ensure that the plant will not be overwatered. Succulents naturally absorb and retain large amounts of liquid, giving them a high risk of drowning.
Just like most houseplants, pencil cacti need sufficient light for them to grow properly. If no natural light is available, a strong artificial light may be used instead. Pencil cacti are fast growers. If left untrimmed, they can grow from 15 to 30 feet (4.572 to 9.144 m) in height. Adequate space must be reserved if the grower wants the plant to grow to its full size.
The stems can be pruned to control the desired size and shape of the plants. Unlike regular plants, the grower should wear gloves and other skin protection before pruning the pencil cactus. This is because whenever the plant's stems are cut or bruised, they emit a caustic white sap as a form of self defense. This is where the name "milk bush" came from.
When the sap comes into contact with the skin, it can lead to irritation or allergic reactions. The effect can range from mild rashes to anaphylactic shock. One characteristic of the pencil cactus is that it produces more sap compared to other succulents of the Euphorbiaceae family. This, together with its numerous stems, increases the chance of contact with the sap during pruning.
Growers should always check if they will have extreme allergic reactions to the plant's sap before they grow it. Children and pets are more susceptible to the sap's effect. Careful considerations must be taken as to where the plant will be placed should the grower decide to cultivate it.