Although most plants on Earth have flowers, the evolutionary origin of the flowers themselves remains a mystery. Flowers are the sexual organs of more than 360,000 species of plants that survive today, all derived from a common ancestor of the distant past. This ancient plant lived between 250 million and 140 million years ago, and it produced its first flowers when the earth was warmer and oxygen and greenhouse gases were abundant than it is now. At that time dinosaurs wandered in the pristine landscape.
But although dinosaurs went extinct 65 million years ago, it seems that we know more about what dinosaurs looked like than the ancestors of flowers.
Part of the reason is that these initial flowers did not leave any traces. Flowers are fragile structures that can only be fossilized in the most fortunate cases. And, with no fossils found 140 million years ago or earlier, scientists have only limited knowledge of what the flowers' final ancestors looked like, until now.
A major new study by an international team of botanists has reconstructed this ancient flower to date. The study, published in the journal Nature Communications, looked not so much on fossils as it looked at the characteristics of 800 extant offspring species.
By comparing the similarities and differences of related flowering plants, the characteristics of their ancestors can be inferred. For example, because half of the flowers of all orchids are mirror images of the other half (bilateral symmetry), we can assume that their ancestors must have had bilateral flowers. By comparing these recent ancestors with each other, it is possible to go back further into the past. And so cycle until we finally reach the very bottom of the flowering plant family tree.
Magnolia flowers
What does it look like?
In some ways, the original flower resembled a modern magnolia flower: it had multiple undifferentiated "petals" (technically called flower covers), arranged in concentric rings. In its center there are multiple rows of reproductive organs, including pollen-producing stamens and ovary that produce ovules. It's hard to resist the temptation to imagine ancient pollinators crawling through this flower, collecting pollen grains while unwittingly helping plants produce seeds.
The new study helps resolve controversies about whether early flowers have different sexes, or whether male and female reproductive organs are combined in the same flower. Previous evidence points to a different answer. On the one hand, one of the earliest branching branches of flowering plants, today represents only a rare shrub, from the Pacific island of New Caledonia, called the interlobite plum, with flowers of male or female nature. On the other hand, most modern species are male-female in the same flower.
Interlobite plum
The authors of this study solved this problem and showed that the ancestors of the flowers were hermaphrodites. This means that early-flowering plants can breed both males and females at the same time. When colonizing new environments, combined genders are advantageous because individuals can be their own partners. In fact, many plant species colonize distant oceanic islands often with hermaphrodites. Perhaps the combination of the sexes helps plants that flower early to win the competition.
The devil is in the details
Although they bear obvious similarities with some modern flowers, their ultimate ancestors have some surprising wonders. For example, botanists have long believed that the flower parts of early flowers were arranged in a spiral around the center of the flower, which can be seen in modern species such as the octagon.
aniseed
However, the new reconstruction strongly suggests that the organs of the early flowers were not spirally arranged, but instead a series of concentric circles or "rotations," like most modern plants. However, early flowers had more rotunded inflorescences, suggesting that flowers became simpler over time. Paradoxically, this simpler structure may have given modern plants a more stable basis on which to evolve and accomplish more complex tasks, such as complex interactions with certain insects, such as orchids, or "flower heads" made up of dozens or hundreds of simpler flowers, such as the sunflower family.
Although we now have a good understanding of what the earliest flower might have looked like, we still know very little about how the flower was formed. The detailed steps that led to its evolution are unclear. Perhaps we will have to wait for the discovery of fossils of new flowers from 250 million to 140 million years ago before we can understand the origins of the most diverse sex structures on Earth.