Many species of charophycean 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 through periods when they are not completely submerged in water. A layer of sporopollenin prevents exposed charophycean zygotes from drying out until they are in water again. This chemical adaptation may have been the precursor to the tough spore walls so important to the terrestrial survival of plants. Such adaptations accumulated by at leastbone population of charophyceans enabled their descendants-the first plants-to live