Epiphytes

Epiphytes are plants that grow on other plants for mechanical support, but do not absorb nutrients from their hosts.  Ferns, bromeliads, and cacti are all epiphytes, but the most common and one of the most beautiful epiphytes of the tropical rainforest  is the orchid.  It is estimated that there are over  20,000 species of orchid in the rainforests.  A single tree may have 300 different species of orchid on it as well as 2000 epiphyte plants.  There are more than 50 thousand species of epiphytes in the world's rainforests. These epiphytes also add up to 45% of the nutrient total of the canopy.

   Epiphytes are unique, because they do not harm the host they grow on.  All epiphytes need nitrogen, nutrients, and minerals to survive, but they all acquire them in different ways.  For example, the bowl shape of an epiphyte called bird's nest fern catches leaves, bird droppings, and other organic matter the falls from above in a miniature compost heap.  The bird's nest fern is unique because its roots grow inward to absorb the collected nutrients.
   Some epiphytes, called bromeliads, have upturned leaves shaped like tanks which they use to collect water.  A single bromeliad can collect up to 25 gallons (100 liters) of water.  These tanks of water also make ideal breeding sites and hiding places for many animals including salamanders, lizards, tree snakes, insect larva, and crabs.  Animals like monkeys and birds, that rarely visit the forest floor, acquire most of their drinking water from bromeliads.  Other bromeliads, called "air plants" or aerophytes, absorb their nutrients straight from the air.  With the help of hair-like scales called trichome cells, the air plants take in water particles from the humid air and nutrients from airborne dust.

   Epiphytes also help trees they live on, by increasing the humidity of the tropical rainforests, which makes it easier for the tropical rainforests to absorb nitrogen from the air.  However, sometimes the epiphytes grow too densely on tree branches, causing the branch or even the entire tree to come crashing down. Sometimes epiphytes can grow to be 1/3 the total weight of the tree they live on.   Many trees have smooth bark or shed their bark in order to discourage excessive epiphyte growth.  Sometimes rough barked trees contain toxins in their bark to control epiphyte growth.