Although algae is usually an aquatic plant, some species can receive free of the water and develop terrestrially on the bark, stems and leaves of trees. Algae most commonly develop trees in moist tropical climates, but many species can develop trees also in temperate subtropical climates.
Trentepohlia
Trentepohlia is a genus of algae that includes about 40 species that frequently grow on trees in tropical and humid subtropical climates. This algae is free-living and terrestrial, and in temperate climates it is most frequently found growing on the bark of trees ; in wetter tropical climates, it may also develop on leaf surfaces. Most species contain an orange pigment that conceals the green colour of their chlorophyll; the algae grows in long filaments, and colonies of the algae seem as brightly coloured orange mounds on the tree bark.
Cephaleuros
Algae of the Cephaleuros genus, together with Trentepohlia, are part of the order Trentepohliales. Like Trentepohlia, Cephaleuros are terrestrial species; they only require water to germinate, therefore they are well-adapted to living on trees instead of in an aquatic environment. Cephaleuros species, like Trentepohlia, contain a orange pigment, and they vary in color from yellow-green to orange. Some species of Cephaleuros may cause blurred red spots on tree leaves, and the infection may be known as “red rust”
Stomatochroon
Stomatochroon is just another part of Trentepohliales, but it differs from Trentepohlia and Cephaleuros in that it grows not to the surface of bark or leaves, but inside the leaf itself in the chambers beneath the pores, or stomata, on the leaf surface. The algae is visible only as it sends up an enlarged “central mobile” that endeavors through the stoma.
Phycopeltis and Physolinum
These two genera are also part of Trentepohliales. The species within these genera typically develop on the surface of leaves, but in humid areas where moist surfaces are common, they can develop everywhere, even on tree permeable and bark objects.
Lichen
Lichen is a structure that commonly grows on trees; it’s due to a symbiotic relationship between fungi and algae. The fungus provides a construction that collects water and nutrients that the algae takes advantage of ; the algae in turn uses its chlorophyll to produce food for both the fungus. Species of the Trentepohlia genus are commonly found in lichens.