Ordovician marine Charophyceae and insights into land plant derivations.

The emergence of land plants was a pivotal development in Earth history. It has been postulated that the evolutionary transition from freshwater streptophyte algae to land plants, or the canalization of plant meiosis, was completed during the Middle Ordovician (460 Ma). However, the absence of undisputed streptophyte algal fossils (for example, Charophyceae) earlier than the late Silurian (425 Ma) has obscured this link between streptophyte algae and land plants. Here we describe a marine Charophyceae fossil, Tarimochara miraclensis gen. et sp. nov., from early and middle Katian (Late Ordovician, ~453-449 Ma) marine limestones in northwestern China. This discovery demonstrates that at least some species of Charophyceae inhabited shallow normal marine environments at that time. Moreover, these early Charophyceae show that some key morphological innovations associated with an evolutionary transition between streptophyte algae and land plants had occurred before the early Katian. This provides crucial evidence relevant to the origins of land plants.