Thursday, May 7, 2009

The Evolution of Plants

Spring is that time of year when we tend to focus on plants. After a long, cold, bleak winter, we appreciate the greenery, flowers, fragrance and unbridled growth of spring. What better time to consider the natural history of plants?

Life evolved in the sea, some 3.6 billion years ago; for most of that time, plants and animals remained in the oceans, not yet equipped to colonize the land. Then, during the Silurian Period (about 420 million years ago), plants ventured onto the continental shores, nourished by the waves and tides. Over the eons, as they evolved stems, root systems and leaves, plants diversified and spread across the landscape, their seeds dispersed by wind, water and primitive animals. Ferns and the first tree-like plants appeared in the Devonian Period (about 375 MYA) while conifers evolved during the Pennsylvanian Period, some 300 MYA.

Flowering plants graced the scene during the Jurassic Period, about 180 MYA, cross-pollinated by the wind or by flying insects that first appeared back in the Mississippian Period (325 MYA); social bees would not appear until the Cretaceous (some 80 MYA). Broad leaf trees also evolved during the Cretaceous (the reign of Tyrannosaurus rex) but grasses would not appear until the Eocene-Oligocene (about 40 MYA), drawing small, woodland mammals onto the nutritious plains and triggering the age of Tertiary megafauna.