Evolutionary History of Plants

Evolutionary History Of Plants

The evolution of plants has resulted in increasing levels of complexity, from the earliest algal mats, through bryophytes, lycopods, ferns to the complex gymnosperms and angiosperms of today. While many of the groups which appeared earlier continue to thrive, especially in the environments in which they evolved, for a time each new grade of organisation became more "successful" than its predecessors.

In the Ordovician period, around 450 million years ago, the first land plants appeared. These began to diversify in the late Silurian Period, around 420 million years ago, and the results of their diversification are displayed in remarkable detail in an early Devonian fossil assemblage from the Rhynie chert. This chert preserved early plants in cellular detail, petrified in volcanic springs.

By the middle of the Devonian Period, most of the features recognised in plants today are present, including roots, leaves and secondary wood; and, by late Devonian times, seeds had evolved. Late Devonian plants had thereby reached a degree of sophistication that allowed them to form forests of tall trees.

Evolutionary innovation continued into the Carboniferous period and is still ongoing today. Most plant groups were relatively unscathed by the Permo-Triassic extinction event, although the structures of communities changed. This may have set the scene for the appearance of the flowering plants in the Triassic (~200 million years ago), and their later diversification in the Cretaceous and Tertiary. The latest major group of plants to evolve were the grasses, which became important in the mid Tertiary, from around 40 million years ago. The grasses, as well as many other groups, evolved new mechanisms of metabolism to survive the low CO₂ and warm, dry conditions of the tropics over the last 10 million years.