Ferns and bromeliads have evolved unusual ways of storing water in the rainforest environment.
The roots of many epiphytic ferns bind fallen leaves and other debris together. They gradually decompose to a peaty material that can hold a great deal of water
Some of these ferns, such as the bird's nest fern, Asplenium nidus, of Southeast Asia, and its close African relative, Asplenium africanum, have a rosette of long strap-shaped leaves forming a cup within which litter can gather.
Others, such as Drynaria, have two kinds of leaves. Some are tall, green and produce the plant's reproductive units, the spores. Others are short, stiff, brown and oak-leaf-shaped and help to trap litter.
The platycerium, or staghorn fern, also has two types of leaves.
Some of the leaves are upright and forked repeatedly like horns. The others are almost circular and remain flat against the trunk of the supporting tree, lying one on top of the other and forming a mass of peaty material.
Bromeliads
Some bromeliads root in the ground like other plants.
Others, including the pineapple, have a normal but rather restricted root system supplemented by extra roots that grow from the stem and absorb water and nutrients that accumulate among the leaf bases.
The third group of bromeliads includes the tank-epiphytes.
Small roots anchor the tank-epiphyte to its supporting branch. The leaf bases are broad and pressed tightly together to form a water-holding tank, or cup. The tank's capacity ranges from less than half a pint up to 12 gallons or more.
Tank-epiphytes absorb water from their built-in reservoir through umbrella-shaped scales, trichomes, which stand in a little hollow in the leaf surface.
When wet, they expand and let water into the hollow below the umbrella rim. On drying, the leaf shrinks and pulls down the umbrella, sealing off the hollow and preventing water loss from the delicate absorbing cells at its base.
Many other things besides water accumulate in the tank - rotting leaves, old flowers and the droppings of animals and birds that feed and drink at the tank.
This debris releases nutrients that are absorbed by the plant. The nutrients also support a thriving miniature ecosystem.
The material is decomposed by bacteria and protozoa. Larger protozoa, tiny crustaceans and mosquito larvae, prey on these and are in turn food for dragonfly larvae.
The insects that visit the water are prey for birds, salamanders and frogs.
Some bromeliad frogs may spend their entire lives in the tank of a bromeliad.
Some bromeliads have fleshy fruits with seeds surrounded by a sticky pulp that may help to glue the seedling in position until it grows enough roots to attach itself.
Bromeliads are often pollinated by hummingbirds.
Bromeliad flowers are usually bright and attractive or surrounded by striking petal-like bracts. The flowers make them attractive houseplants.