Analyses of nuclear and chloroplast genes from a wide range of plants and algae indicate the charophytes are the closest living relatives of land plants. Many species of charophyte algae inhabit shallow waters around the edges of ponds and lakes, where they are subject to occasional drying. In such environments, natural selection favors individual algae that can survive periods when they are not submerged in water. In charophytes, a layer of a durable polymer called sporopollenin prevents exposed zygotes from drying out. A similar chemical adaptation is found in the tough sporopollenin walls that encase the spores of plants. The accumulation of such traits by at least one population of charophyte ancestors probably enabled their descendants to live permanently above the waterline. These evolutionary novelties opened a new frontier: a terrestrial habitat that offered enourmous benefits.