The Arid House

All the plants in the Arid House are adapted to drought. Many take up water rapidly and store it in their succulent stems and leaves during infrequent periods of rainfall. Some of these plants use 'crassulacean acid metabolism' (CAM) – a particularly efficient form of photosynthesis in which their pores (stomata) remain closed during the day to reduce water loss. At night, these pores then open to absorb carbon dioxide. Rainfall triggers flowering in arid plant communities. Mass flowerings often coincide with the migration of pollinating birds. Other species flower at dusk when pollinating bats emerge, for example cacti such as Cereus uruguayanuswhich can be seen growing in the Arid House. The most prominent plants in the Arid House are the giant euphorbia, and next to it, a similar-sized cactus which stand over six metres tall in the centre. These plants evolved on the continents of Africa and North America respectively. Because they both evolved adaptations to survive arid conditions, they look very similar, even though they are unrelated – an example of convergent evolution.