Fossilized pollen grains discovered in Switzerland. Hochuli et al/Frontiers in Plant Science

April showers bring May flowers nowadays, but hundreds of millions of years ago, they didn’t. Flowering plants didn’t arise until dinosaurs roamed the Earth -- though according to new research, they popped up 100 million years earlier than we thought.

At some point, a group of ancient plants that would eventually give rise to flowering plants diverged from a larger group called gymnosperms, whose modern representatives include pine trees, cycads and other seed-bearing plants that don’t have flowers or fruit. But drawing up the timeline for flower evolution has proved difficult. It’s hard enough to find fossilized dinosaur bones; it’s even harder to find a rich fossil record of plants from hundreds of millions of years ago.

To look for ancient flowers and their ancestors, scientists typically search for the signs of ancient pollen grains (leaves and seeds are much more susceptible to the forces of nature and time). To date, the most complete collection of fossilized flower pollen dates back to the Early Cretaceous, about 140 million years ago, so that’s about when scientists peg the origin of flowering plants, also known as angiosperms.

Now, geologist Susanne Feist-Burkhardt and University of Zurich paleontologist Peter Hochuli say they’ve found six different kinds of fossilized grains that look like pollen from the earliest known flowering plants, dating back to the Middle Triassic period. They reported their find in the journal Frontiers in Plant Science on Tuesday.

Based on their examinations of the fossilized grains with powerful microscopes, the researchers say the pollen appears to belong to an ancient genus of plants called Afropollis. Furthermore, the plants seem to be related to pollen that Hochuli and Feist-Burkhardt found in samples taken from the Barents Sea, 3,000 kilometers (1,864 miles) south of the site of the current study. Altogether, the evidence implies that flowering plants may have arisen in the Early Triassic -- between 252 and 247 million years ago.

At the time that these plants flourished, Switzerland was a subtropical region, but it was much drier than the ancient Barents Sea area. The presence of pollen grains in both regions suggests that ancient flowering plants were adaptable organisms.

“Since this group produced a wide variety of … pollen grains and could adapt to various environments, we expect that they may be found in other areas and in other … environmental contexts,” the authors wrote.

SOURCE: Hochuli et al. “Angiosperm-like pollen and Afropollis from the Middle Triassic (Anisian) of the Germanic Basin (Northern Switzerland).” Frontiers in Plant Science published online 1 October 2013.