Gene tests help solve 'abominable mystery' of flowering plants

Charles Darwin called it an "abominable mystery" and it has perplexed generations of botanists who have tried to explain the sudden and dramatic appearance of flowering plants 130 million years ago.

For tens of millions of years, land plants consisted of mosses, ferns, firs and conifers. But then, the fossil record shows, there was an explosion in a new kind of plant – one with flowers that soon became the most diverse and dominant botanical group.

Now scientists believe they are closer to solving Darwin's mystery with the publication yesterday of two studies showing how today's 400,000 species of flowering plants are related to one another, and, crucially, when they came into existence.

The findings show that all five major groups in the family tree of flowering plants originated within the space of just five million years. The research also points to unusual relationships, such as the close genetic similarity between the two largest groups of flowering plants, the monocots – which include grasses and orchids – and the eudicots, such as the sunflowers, tomatoes and cabbage family.

But it is the relatively sudden evolution of all the flowering plants from a common ancestor – confirmed by the genetic analysis of more than 100 different species – that has amazed the scientists involved.

"Flowering plants today comprise around 400,000 species, so to think that the burst that gave rise to almost all of these plants occurred in less than five million years is pretty amazing – especially when you consider that flowering plants as a group have been around for at least 130 million years," said Pam Soltis of the University of Florida.

Professor Robert Jansen of the University of Texas at Austin said the explosion in diversity of the flowering plants was often referred to as the Big Bang of botany and determining the genetic similarities between plants today was the key to understanding what happened so long ago.

The fossil record shows the first plants to live on land 425 million years ago were mosses. They was followed by ferns, firs, ginkgoes and conifers – along with other varieties – until the flowering plants appeared.

Today, the flowering plants comprise at least 60 per cent of all green plant species. The two studies, published in the Proceedings of the National Academy of Sciences, collectively analysed the DNA of 142 genes from 109 species drawn from all five major groups of flowering plants.

Professor Mark Chase of the Royal Botanic Gardens at Kew said a possible explanation for the success of flowering plants was the evolution of unique cells that could carry water efficiently from the roots to the leaves.

The ability to decipher the complete genome of the chloroplast – the green photosynthetic structure which evolved just once on land plants – led to the latest discovery.