Although most species of plants on Earth have flowers, the evolutionary origin of flowers themselves are shrouded in mystery. Flowers are the sexual organs of more than 360,000 species of plants alive today, all derived from a single common ancestor in the distant past.
This ancestral plant, alive sometime between 250 and 140 million years ago, produced the first flowers at a time when the planet was warmer, and richer in oxygen and greenhouse gases than today. A time when dinosaurs roamed primeval landscapes.
But despite the fact dinosaurs went extinct 65 million years ago we have a better idea of what an Iguanodon looked like than of how the ancestral flower was built.
This is partly because these first flowers left no traces. Flowers are fragile structures that only in the luckiest of circumstances can be transformed into fossils.
And, as no fossil has been found dating back 140 million or more years, scientists have only had a limited sense of what the ultimate ancestor would have looked like. Until now.
A major new study by an international team of botanists has achieved the best reconstruction to date of this ancestral flower. The research, published in Nature Communications, relies not so much on fossils as on studying the characteristics of 800 of its living descendant species.
By comparing the similarities and differences among related flowering plants, it is possible to infer the characteristics of their recent ancestors.
For example, because all orchid species have flowers in which one half is the mirror image of the other (bilateral symmetry), we can suppose that their ancestor must have had bilateral flowers.
By comparing those recent ancestors to each other it is then possible to go a step further back in time, and so on, until eventually we reach the base of the flowering plants’ family tree.
So what did it look like?
In some respects, the original flower resembles a modern magnolia: it has multiple, undifferentiated “petals” (technically tepals), arranged in concentric rings.
At its centre there are multiple rows of sexual organs including pollen-producing stamens and ovule-bearing ovaries.
It is hard to resist the temptation to imagine ancient pollinators crawling in this flower, collecting pollen grains while unknowingly helping the plant to produce seeds.
A controversial sex life
The new study helps to settle the controversy about whether early flowers had separate sexes, or whether both male and female reproductive organs were combined in the same flower.
Previous evidence pointed to different answers. On the one hand, one of the earliest diverging lineages of flowering plants, represented nowadays only by a rare shrub from the Pacific island of New Caledonia called Amborella, has flowers that are either male or female.
On the other, most modern species combine both sexes in the same flower.