How flowering plants became dominant in ecosystems across globe?

We may generally think that during the whole course of the long history of life, or at least much of it, nature has been ornamented by flowers. This notion, however, is wrong. In fact, flowering plants came very late to the arena of nature, some 290 million years after the first known land plants appeared on the surface of our planet. But how did flowers evolve and rapidly become dominant in ecosystems across the world? This persisting question and the “abominable mystery,” as Charles Darwin once put, seems to have been resolved at last, a new study suggests.

Flowering plants, technically known as angiosperms, presently constitute about 90 percent of all living plant species, including most food crops, and are easily characterized by their flowers, endosperm within their seeds, and the production of fruits that contain the seeds, contrasting with gymnosperms, or non-flowering plants, a group that includes conifers, cycads, and Ginkgo.

As far as paleontological excavations and phylogenetic studies show, the ancestors of angiosperms diverged from gymnosperms in the Triassic Period, from 245 to 202 million years ago (mya), and the first true flowering plants emerged some 160 mya, in the upper Jurassic Period, and became widespread by 120 mya, in the lower Cretaceous Period. They finally managed to replace conifers, which predate them, as the dominant trees from 100 to 60 mya, in the upper Cretaceous Period, and began changing the landscape from muted green to a riot of vibrant color.

A new research, whose results were published in the journal PLOS Biology earlier this week, suggested that the key to the puzzling mystery of incredible success of flowering plants is in their genome size.

To see whether the size of the plant's genetic material, or genome, might be the main driver behind the tremendous success, researchers analyzed data kept by the Royal Botanic Gardens, Kew, on the genome size of hundreds of plants, including angiosperms, gymnosperms, and ferns. They then compared the genome size of these plants with their anatomical features such as the abundance of pores on leaves.

They found that there was “strong evidence” that the success and rapid spread of flowering plants across the globe was down to “genome downsizing.” That is, angiosperms started shrinking the size of their genome, which is contained within the nucleus of the cell, resulting in producing smaller cells.

“It really comes down to a question of cell size and how you can build a small cell and still retain all the attributes that are necessary for life,” said Kevin Simonin from San Francisco State University in California, the United States, who co-authored the study.

The genome-downsizing allows greater carbon dioxide uptake and carbon gain from photosynthesis, a process during which plants employ light energy to turn carbon dioxide and water into glucose and oxygen. The advantage, in turn, helps flowering plants pack more veins and pores into their leaves, maximizing their productivity.

According to Simonin and co-researcher Adam Roddy, genome-downsizing occurred only in the angiosperms, and this was “a necessary prerequisite for rapid growth rates among land plants.”

“The flowering plants are the most important group of plants on Earth and now we finally know why they have been so successful,” they added.

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