Succulents are plants that have specialized to survive drought and harsh environmental conditions by storing water in their fleshy tissues. They have many distinctive and unusual shapes which never cease to amaze me. Cacti (Cactaceae) are a specific family of succulents that's have areoles, pad-like buds from which spines, flowers, and shoots grow.
This page contains 12 galleries with over 150 photos of succulents and cacti.