In 1867 Schwendener announced to the scientific world his hypothesis that lichen was formed by two separate organisms, a fungus and an alga. At the time his theory was largely rejected, but it was afterwards proven to be factual.- Lichen (Wikipedia)
A lichen (/ˈlaɪkən/ LY-kən, UK also /ˈlɪtʃən/ LITCH-ən) is a composite organism that arises from algae or cyanobacteria living among filaments of multiple fungi species in a mutualistic relationship. Lichens are important actors in nutrient cycling and act as producers which many higher trophic feeders feed on, such as reindeer, gastropods, nematodes, mites, and springtails. Lichens have properties different from those of their component organisms. They come in many colors, sizes, and forms and are sometimes plant-like, but are not plants. They may have tiny, leafless branches (fruticose); flat leaf-like structures (foliose); grow crust-like, adhering tightly to a surface (substrate) like a thick coat of paint (crustose); have a powder-like appearance (leprose); or other growth forms.