The Pencil Cactus 6in, commonly referred to as the milk bush or Euphorbia tirucalli, is a fascinating and adaptable plant that makes a great addition to any indoor garden. Although it's called a cactus, it is actually a succulent shrub known for its unique, elongated stems that resemble unsharpened pencils. This drought-tolerant plant thrives in low-humidity environments and grows beautifully in pots, provided they have drainage holes to prevent excess moisture buildup.