The pencil cactus, otherwise known as a 'milk bush' or euphorbia tirucalli, is a variety of cacti known for its signature, vertical pencil-like branches that grow in a candelabra pattern.

One more comment: Some plants that are called "cactus" belong to a different or related group of plants, such as succulents or euphorbia. We've included them in our list, however, because they're ...