Green Algal Conquest of the Land: Many Conquests, One Victory?

Life on earth originated in a wet world and remained there for millions of years until the first terrestrial invaders made their initial forays into a new and unexploited terrestrial habitat. Although cyanobacteria, and perhaps fungi as well, were important participants in the conquest of the land, it was the evolution green algae into the initial land plants that started amazing evolution and diversification the terrestrial flora and fauna with which we are now familiar. Given the paradigm that life arose in the sea, it is perhaps surprising to find that freshwater green algae – not marine forms – were the successful conquerors, i.e. the algae that gave rise to the land plants. The first land colonizers were, of necessity, primary producers (i.e. food for organisms that arrived or evolved later) and were likely to have been cyanobacteria (blue‐green algae), followed by green algae (at least four separate invasions) and fungi, which also made a successful assault on land together with algae in the form of lichens. The symposium will survey recent studies on these groups and their habitats, and describe how these colonizers changed and were changed by adaptations to the new, dry world. It will explore the question: ‘Why did only one group of terrestrial green algae give rise to the land plants?’ The success of these colonizers is relevant to all subsequent terrestrial life (including ourselves), as well as the search for extraterrestrial life, which, if it exists, is presumed to have begun in an aquatic environment.