More than two thirds of the world's plant species are found in the tropical rainforests: plants that provide shelter and food for rainforest animals as well as taking part in the gas exchanges which provide much of the world's oxygen supply.
Rainforest plants live in a warm humid environment that allows an enormous variation rare in more temperate climates: some like the orchids have beautiful flowers adapted to attract the profusion of forest insects.
Competition at ground level for light and food has lead to evolution of plants which live on the branches of other plants, or even strangle large trees to fight for survival.
The aerial plants often gather nourishment from the air itself using so-called 'air roots'. The humidity of the rainforest encourages such adaptations which would be impossible in most temperate forests with their much drier conditions.
Bromeliads
Bromeliads are related to the pineapple family. Their thick, waxy leaves form a bowl shape in the centre for catching rainwater. Some bromeliads can hold several gallons of water and are miniature ecosystems in themselves providing homes for several creatures including frogs and their tadpoles, salamanders, snails, beetles and mosquito larvae. Those that die decompose and furnish the plant with nutrients. One bromeliad was found to contain several small beetles, crane flies, earwigs, a frog, a cockroach, spiders, fly larvae, a millipede, a scorpion, woodlice and an earthworm!
Buttress roots
Most rainforest soil is very poor with all the nutrients available largely remaining at surface level. Because of this rainforest trees have very shallow roots. Some very tall trees have developed ways of obtaining much needed additional support by forming buttressed roots, which grow out from the base of the trunk sometimes as high as 15 ft above the ground. These extended roots also increase the area over which nutrients can be absorbed from the soil.
Carnivorous plants
Some plants are adapted to obtain nutrients from animal matter. The best known of these is probably the Venus fly trap, but more impressive is the pitcher plant Nepenthes rafflesiana, found in southeast Asia. This plant grows to 30 feet tall and may have pitchers 12 inches in length, usually crammed full of digested insects.
Pitcher plants also eat small mammals and reptiles that attempt to steal the insects from the pitcher.
Epiphytes
Epiphytes, or air plants, grow everywhere but can be found mainly on the branches, trunks, and even the leaves of trees. The name 'epiphyte' comes from the Greek word 'epi' meaning 'upon' and 'phyton' meaning 'plant'. Different types of epiphytes may grow on the same tree, including orchids, cacti, bromeliads, aroids, lichens, mosses and ferns. They begin their life in the canopy from seeds or spores transported there by birds or winds.
Lianas
Ninety per cent of the world's vine species grow in tropical rainforests. Lianas are a type of climbing vine found throughout tropical rainforests. They have thick, woody stems and come in various lengths (up to 3,000 ft) and varying shapes. They begin life on the forest floor but depend on trees for support as they climb upwards towards the sunlight they need for survival. They do this by attaching themselves to trees with sucker roots or tendrils and growing with the young sapling, or they climb by winding themselves round the tree's trunk.
When they reach the top of the canopy they often spread to other trees or wrap themselves around other lianas. This network of vines gives support against strong winds to the shallow-rooted, top-heavy trees. However, when one tree falls several others may be pulled down also.
Lianas include rattan palms, philodendron and Strychnos toxifera (from which the deadly poison strychnine is obtained). Rattans, the Asian lianas, have thorny stems and can reach heights of 650 feet (200 m). They are used to make a variety of things including baskets, ropes and wicker furniture.
Orchids
Orchids comprise one of the most abundant and varied of flowering plant families. There are over 20,000 known species and orchids are especially common in moist tropical regions. Although temperate orchids usually grow in the soil, tropical orchids are more often epiphytes which grow non-parasitically on trees.
Orchid flowers vary considerably in shape color and size, although they share a common pattern of three petals and three petal-like sepals. The lower petal has a very distinctive appearance.
Saprophytes
Saprophytes are the organisms that act as the rainforests decomposers, competing with the heavy rainfall which constantly washes away nutrients on the forest floors. Some fungi, called mycorrhizals, are examples of plant life that carry out this function. Decomposers work extremely efficiently and, together with the warmth and wetness which helps accelerate decomposition, can often break down dead animals and vegetation within 24 hours. Decomposition in montane forests, which are colder and less humid, however, can sometimes take up to six weeks.
Many saprotrophs are so small, called microbes, that they cannot be seen with the naked eye. Other decomposers, which include insects, grubs, snails, slugs, beetles and ants, aid in recycling valuable nutrients from dead organic matter which is then released back into the soil to be reabsorbed rapidly by plants and trees. Decayed matter contains essential nutrients like iron, calcium, potassium and phosphorous all of which are necessary to promote healthy rainforest growth. Thus decomposers must work continuously to release these and other elements into the soil.
Stilt or prop roots
Mangrove rainforest trees require a different kind of support system. Mangroves grow in wet, muddy soil at the water's edge which can be subject to tides and flooding. As a means of support they develop several aerial pitchfork-like extensions from the trunk which grow downwards and anchor themselves in the soil trapping sediment which helps to stabilize the tree.
Strangler fig
Most stranglers are members of the fig family. In Spanish they are known as matapalo - 'killer tree'. The seed of the strangler fig starts life as an epiphyte high in the trees, borne by birds and monkeys which eat the fig fruit. The seedling fig sends down long roots to the ground from where it begins to surround the host tree. It grows quickly and eventually suffocates the host: when the host tree dies it leaves an enormous upright strangler with a hollow core.
By using an adult tree as its host, the strangler fig avoids competition for light and nutrients at ground level.
