(I) The algal ancestors of plants may have carpeted moist fringes of lakes or coastal salt marshes over 500 million years ago. (II) Both groups have similar microscopic structures for making their cellulose cell walls and a similar mechanism for forming the cell plate that divides the cytoplasm during cell division. (III) These shallow-water habitats were subject to occasional drying, and natural selection would have favoured algae that could survive periodic droughts. (IV) Some species accumulated adaptations that enabled them to live permanently above the water line. (V) The modern-day green alga Coleochaete may resemble an early plant ancestor, and it grows at the edges of lakes as disk-like, multicellular colonies.