Plant surfaces, like any other surface, provides potential habitats to fungi. We have already mentioned the growth of lichens on tree trunks, branches and twigs; of yeasts on leaves and fruits and in the nectaries of flowers (which, though fluid, are external to the plant); and of rhizomorphs of such pathogens as Armillaria, ‘scrambling’ over the surface of potential hosts. Fungi that live on the surfaces of plants are called epiphytes. Some show special adaptations to the plant surface, which is a challenging environment, being dry, waxy and exposed to direct sunlight. So epiphytes are often pigmented (particularly melanised) to protect them from UV radiation, and some can digest lipids sufficiently to use the waxy layer covering the leaf epidermis. The yeast form usually has a short life cycle, which enables yeast epiphytes to multiply even if favourable conditions last only a short time.
Updated December 17, 2016