Flowering plants, which only date back 125 million years, are the most successful group of land plants. They evolved from seed plants and diversified into monocots and dicots. Flowers allow for symbiotic partnerships with pollinating insects, aiding genetic diversity and resistance to disease. By the end of the Cretaceous period, half of today’s major flower groups had evolved and accounted for 70% of global plant species.
Although land plants have been around for 470 million years or more, the earliest evidence of flowering plants, in the form of the fossil Archaefuctus liaoningensis, dates back to just 125 million years ago, in the early Cretaceous period. This means that flowers have only existed about a quarter of the time of land plants in general. Fossil evidence of pollen, considered a strong indication of flowering plants, is somewhat older, dated to about 130 million years ago.
The evolution of flowering plants was slow in coming, but today they are the most successful group of land plants, found on every continent except Antarctica and on remote islands. Their sudden appearance and success was so extreme that Charles Darwin called it an “abominable mystery”. Since Darwin’s time, however, more fossils have been found that reveal a series of intermediate steps before full-fledged flowers.
Plant evolution is generally one in which groups that exploit fundamental evolutionary innovations – such as vascular tissue, bark, seeds or flowers – have a tendency to almost completely replace more primitive plants when they really get started. Furthermore, these evolutionary innovations tend to emerge in the most complex plants of the time. As a result, flowering plants evolved from the more sophisticated seed plants, which themselves had replaced most seedless plants some 370 million years ago, during the late Devonian period.
Flowers are a highly successful evolutionary innovation because they allow for a more complex range of interactions with other organisms. This opens up various symbiotic partnerships, particularly with pollinating insects such as bees. The constant exchange of pollen between plants, facilitated by bees, helps these plants remain genetically diverse and resistant to disease or other ailments.
Flowering plants diversified into the two main groups, monocots and dicots, only 5 to 10 million years after their initial evolution. By the end of the Cretaceous, 65.5 million years ago, half of today’s major flower groups had evolved and they accounted for 70% of global plant species. The success of plants during this period had led scientists to speculate that dinosaurs might have gone extinct by eating flowers. This was before scientists came to agree that dinosaurs most likely went extinct as a result of an asteroid impact.
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