A lichen is a composite organism that arises from algae or cyanobacteria living among filaments of multiple fungi species in a mutualistic relationship. 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 flat leaf-like structures grow crust-like, adhering tightly to a surface (substrate) like a thick coat of paint have a powder-like appearance or other growth forms.