Leaf-inhabiting lichens (foliicolous lichens) are characteristic of rainforest jungle habitats. They use the long-lived leaves of angiosperm plants as a surface for growing, and they may also benefit from increased water vapor presence because of leaf evapotranspiration.
Because of poor soils and other conditions, tropical rainforest plants retain their leaves last for several years, providing an ideal substratum for the lichens. As epiphytes, the lichens do not obtain nutrients from the host plant. During wet periods, the lichens are translucent and do not interfere with leaf photosynthesis.
In this semi-dark environment, both plants and lichens have evolved to do photosynthesis in attenuated light conditions. Even the algal hosts of these lichens are unusual, and do optimum photosynthesis under the cover of the jungle canopy.
Little is known about leaf lichens, taxonomically, morphologically, or ecologically. They may participate in multiple symbioses like many of the jungle organisms.
For great closeups of leaf-inhabiting lichens see: