A group of plants that live in conditions with extreme water shortages. They come in a wide range of genera and families and many different shapes and sizes and adapt to the environment in a number of ways. In order to minimise transpiration to reduce moisture loss to a minimum, their leaves have been shed or become spines, and even photosynthesis differs somewhat from that of other plants. Their physiological processes have been altered, with their stomata closing for most of the day and opening at night, which is when they capture CO2. They are spread across the arid and semi-arid subtropical areas of the world. Succulents are found on all 5 continents, but cacti are an almost exclusively American family.