Earlier origin for flowering plants

Flowering plants may have originated more than 100 million years earlier than previously thought, according to scientists in Switzerland and Germany.

The previously oldest known flowering plant-like pollen dates from the Early Cretaceous period.

But the team described six types of fossil pollen grains from older Middle Triassic core samples that closely resemble these earliest examples.

The research is published in the journal Frontiers in Plant Science.

Flowering plants – also known as angiosperms – are the most numerous and diverse group of seed-producing plants on land.

All seed-producing plants make pollen, with each grain enclosing the developing male cell used in sexual reproduction.

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“That’s why plants developed a very tough and resistant wall of organic matter to protect them,” explained Professor Peter Hochuli from the University of Zurich, Switzerland.

“In the fossil record we find only this protective wall of the pollen grains.”

Based on the increase in abundance and diversity of flowering plants during the Early Cretaceous – approximately 140 million years ago – it has been assumed that they originated in this period.

In the older Triassic samples, Prof Hochuli and his team used confocal laser scanning microscopy to obtain high resolution, three-dimensional images and identified six distinct types of fossilised flowering plant-like pollen based on size, patterning and structure.

“With a few differences…the pollen from the Middle Triassic look exactly the same as the angiosperm pollen from the Early Cretaceous,” explained Prof Hochuli.

Taken with previous reports of pollen in Triassic sediment from the Barents Sea with similar features to these suggests that flowering plants originated over a 100 million years earlier in the Middle Triassic period – circa 243 million years ago.

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I think part of it is a gap in the observation, one finds what is already known”

Prof Peter Hochuli
University of Zurich
“The number of species found in Switzerland and the from the Barents Sea suggest a rather high diversity and that the group might originate from the Early Triassic or the Late Palaeozoic era,” he said.

However, this does leave a period of 100 million years for which there are no records of flowering plant-like pollen.

“I think part of it is a gap in the observation, one finds what is already known. Without my experience from the Barents Sea, I think I would have missed the few tiny grains,” Prof Hochuli told BBC Nature.

As the described pollen grains were rare, making up less than 1% of the pollen count, they cannot tell us much about the period’s climate.

But according to Prof Hochuli: “The accompanying pollen assemblages tell us that during the Middle Triassic the climate was warm/hot and arid in Central Europe/Switzerland and still warm, but more humid in the Barents Sea area.”

In the future they could go on to describe these pollen types as new species. But Prof Hochuli is more interested in finding evidence from other places and from even older sediments, such as the Early Triassic, “that’s our next step”.b