Pitcher plants (Nepenthes sp.) growing on a tree. Pitcher plants are able to grow on soils with very few nutrients because they have evolved the ability to catch and digest insects. The interior of the 'vase' or 'trumpet' is slippery and contains downward-pointing spikes so that once an insect has entered it will be unable to leave, slipping to the bottom. Liquid at the base contains digestive enzymes which digest the insects, providing phosphorus and nitrogen for the plants. Photographed in Bako National Park, Sarawak in Malaysia.