One of the reasons they are trending right now is because they are a succulent. They store water in their stems and roots and can live up to a year without rain. It can be difficult to grow a barrel cactus indoors. Without adequate lighting, your plant will become spindly over time and lose its color. These cacti grow in the very typical shapes of paddles or mostly round shapes. The most popular cacti from Madagascar are small shrubs, with thick succulent leaves. These leaves can be found in different forms and shapes.