It's more than a plant with stickers. To a botanist it is a plant that has certain characteristics that place it in the family of plants known as the Cactaceae . A unique feature of cacti are areoles, small areas on the stem which contain spines. Areoles are also the places where flowers, new stems, or roots arise. A cactus is a perennial, that is it can live for many years.
Most cacti are without leaves.
The stem is fleshy or succulent and contains water-storing tissue. These features allow the plant to withstand periods of drought, which is a common occurrence in the habitats where cacti grow. All cacti can be called succulents, but not all succulents are cacti. In addition to the Cactaceae , succulents occur in the lily, milkweed, daisy, stonecrop, and about 45 other plant families. T he vast majority of cacti live in desert and semi-desert habitats.