A lichen (/ˈlaɪkən/ LY-kən, also UK: /ˈlɪtʃən/ LICH-ən) is a composite organism that arises from algae or cyanobacteria living among filaments of multiple fungi species in a mutualistic relationship.[4] Lichens have properties different from those of their component organisms. They come in many colors, sizes, and forms and are sometimes plant-like, but lichens are not plants. They may have tiny, leafless branches (fruticose); flat leaf-like structures (foliose); crust-like, adhering tightly to a surface (substrate) like a thick coat of paint (crustose);[5] a powder-like appearance (leprose); or other growth forms.[6]
nounRust is an iron oxide, a usually reddish-brown oxide formed by the reaction of iron and oxygen in the catalytic presence of water or air moisture. Rust consists of hydrous iron(III) oxides (Fe2O3·nH2O) and iron(III) oxide-hydroxide (FeO(OH), Fe(OH)3), and is typically associated with the corrosion of refined iron.
noun