Today, the vast majority of the plants in the world are angiosperms (flowering plants). They provide our food and those of the animals we eat, as well as produce the air we breathe and the beauty on which we thrive. Apart from the great conifer forests of the north, non-flowering plants like ferns and horsetails have been reduced to ecological niches. Surprisingly, however, the story of flowers is not one of a new innovation swiftly displacing its inferior predecessors. Instead, there was a long delay between the arrival of the first flower and the conquest of the planet, during which various sorts of non-flowering plants maintained dominance.
Dr Hervé Sauquet of the Royal Botanic Garden Sydney and the Australian Institute of Botanical Science has published in Nature Ecology and Evolution the most comprehensive study yet of the angiosperm family tree. His research confirms what others had suspected, that flowers first appeared at least 140 million years ago, possibly much earlier, and most of the families we know today date back at least 100 million years. Yet the stunning abundance that seems normal to us came much later.
“Fossils are the most important pieces of evidence needed to understand these important evolutionary questions around angiosperm divergence times,” Sauquet said in a statement. “Previous studies of this nature only used 30 to 60 fossil records and we wanted to increase this number significantly and set a higher standard for fossil calibration by documenting every part of the process. We often had to translate records from different languages and do relentless detective work to get centuries-old as well as the latest fossil descriptions in our hands.”
Using this data source, Sauquet concluded that individual angiosperm families took between 37 and 56 million years from their appearance to reach their “crown”, the last common ancestor of existing abundance. For something like a third of their time on Earth, these families failed to bloom into anything close to their potential.
When asked the reason for such a delay, Sauquet told IFLScience that “the short answer is we don't know." The capacity of flowers to be pollinated by insects, a far more efficient intermediary than the wind or other pre-existing methods, has been a big part of flowering plants' success.
“It's possible the first pollinators were not doing such a great job” Sauquet said, and it took a long time for them to develop shapes suited to optimum pollen transfer. However, he admits this is “just an idea.”
The dates at which most angiosperm families diversified are imperfectly established, but many may coincide with the K-P boundary, when non-avian dinosaurs went extinct. Certainly most of the families we know preceded this disaster, and were much more likely to make it through than animals, particularly vertebrates, even if individual species died out.
“It's not clear if the asteroid had a great effect,” Sauquet told IFLScience, but it is possible the huge turnover of life on Earth gave these plants an opportunity they seized, while older lineages declined or went extinct entirely.