The identifying characteristics of a succulent plant are that their stems, roots and leaves have evolved to retain water with great efficiency. To this end, many succulents have spines or leaves that are fleshy.
Types of succulents include kalanchoe; sedum; aloe; agave and cacti. Cacti are a special type of succulent because they have structures called areoles, which are bumps on the skin of the plant. If the cactus has spines, they grow out of these areoles.
Other succulent plants are types of cereus; crassula; hen and chicks; echeveria and yucca.
Some succulents have leaves that are covered with a layer of wax. The leaves may also be narrow. Other succulents have leaves that are ribbed and can expand when the plant takes up a quantity of water. Some plants do without leaves at all and develop needles or hairs. Succulents also have very small pores to keep water from evaporating. Since many succulents are desert plants, most do best in warm climates. However, some succulents, such as certain types of agave, are surprisingly cold tolerant.
Many types of succulents are also excellent houseplants. They aren't grown in the usual loamy potting soil but in soil that is formulated for them. This soil is chunky and drains quickly.