When Did Flowering Plants Evolve?
You might think that flowering plants (angiosperms) have been around forever, but they haven't. Though land plants have been around for 470 million years or longer, the earliest evidence of flowering plants, in the form of the fossil Archaefructus liaoningensis, dates to just 125 million years ago, in the early Cretaceous period. This means that flowering plants have only existed for about a quarter of the time of land plants in general. Fossil evidence of pollen, considering indicative of flowering plants, is a bit older, dated to about 130 million years ago.
The evolution of flowering plants was a long time in coming, but today, they are the most successful group of land plants, found on every continent but Antarctica, and on remote islands thousands of miles from the mainland. The abrupt appearance and success of flowering plants was so extreme that Charles Darwin called it an "abominable mystery." However, since Darwin's time, more fossils have been found that reveal a series of intermediate steps before full-fledged flowers.
The evolution of plants is generally one where groups that exploit fundamental evolutionary innovations, such as vascular tissue, bark, seeds, or flowers, have the tendency to almost completely replace more primitive plants when they really get going. Furthermore, these evolutionary innovations tend to emerge in the most complex plants at the time. Accordingly, flowering plants evolved from the most sophisticated seed plants, which themselves had replaced most seedless plants about 370 million years ago, during the late Devonian.
Flowers are a very successful evolutionary innovation because they permit a more complex range of interactions with other organisms, opening up various symbiotic partnerships, especially with pollinating insects such as bees. The constant exchange of pollen between plants, facilitated by bees, helps flowering plants to stay genetically diverse and resistant to disease or other hardship.
Flowering plants diversified into the two main groups, monocots and dicots, just 5-10 million years after they initially evolved. By the end of the Cretaceous, 65.5 million years ago, half of today's main groups of flowering plants had evolved, and they accounted for 70% of global plant species. The success of flowering plants around this time had caused scientists to speculate the the dinosaurs may have gone extinct by eating flowers. This was before scientists came to agree that the dinosaurs went extinct from an asteroid impact.
Written by Michael Anissimov
