Growth of Lichens

Starvation is a condition necessary for the growth of lichens. When moisture is overly abundant, the alga outgrows the fungus. When nutrients are in generous supply, the fungus outgrows the alga. Either of the preceding two conditions is ruinous to the association. Many species grow very slowly. In the laboratory, it can take one year to obtain a lichen one millimeter in diameter. There are forms that grow much more rapidly, however.