The plants living on a single rainforest tree can weigh several tonnes
Orchids, bromeliads and ferns perched high in a rainforest canopy never touch soil, drinking from rain, fog and mist instead. These epiphytes use trees only as scaffolding, not food, yet their combined weight on one tree can reach several tonnes, and frogs raise families in the water pools they hold.
An epiphyte, from Greek for upon a plant, grows on another plant, known as its phorophyte, for support alone. That distinguishes it from a parasite, which steals nourishment. Nutrients arrive from rain and dew, from debris collecting around roots, from substances washing off the host, and through nitrogen fixation. The popular label air plant is misleading, since many seaweeds and algae live the same way underwater.
Almost every major plant group has epiphytic members, but flowering plants dominate, with about 24,000 species or 89 percent of land epiphytes. Ferns come next with around 2,800, and roughly a third of all fern species live this way. The Neotropics alone may hold some 15,500 epiphytic vascular plants. Botanists split them into holo-epiphytes such as orchids, which never contact the ground, and hemi-epiphytes such as strangler figs, which start aloft and later send roots down to the soil.
Height has advantages: more light than the forest floor and fewer grazing animals. The cost is water scarcity, so many rely on CAM photosynthesis, a water-saving chemistry used by perhaps half of epiphytic orchids as well as bromeliads such as Tillandsia and some cacti. Collectively they change their surroundings, storing water in the canopy, reducing the amount reaching the soil, and cooling and humidifying the host's crown. Europe has no rooted epiphytic plants beyond the odd fern, but damp western coasts support rich mosses and lichens on trees.
In the sea the cast shifts to algae, sponges, bryozoans and many other organisms settling on seagrasses and seaweeds. Photosynthetic epiphytes can supply 20 to 60 percent of an ecosystem's primary production and feed snails and nudibranchs. Too many, though, block light from their hosts, and surges linked to nitrogen runoff from farms and storm water can damage or kill seagrass beds.
Source: Epiphyte
