Researchers map ’super-tree’ of flowering plants, solving Darwin’s "abominable mystery"

The secret of how flowering plants evolved into one of the Earth’s most dominant and diverse groups of organisms is revealed in study led by researchers from the Royal Botanic Gardens, Kew and Imperial College London.

Described by Charles Darwin as an “abominable mystery”, the team publish the first complete evolutionary ’super-tree’ of relationships among all families of flowering plants in current edition of the Proceedings of the National Academy of Science.

Using a combination of DNA sequence data and statistical techniques for analysing biodiversity, the team concludes that Darwin’s suspicion that there is not a simple explanation for the large biodiversity of flowering plants was correct.

Dr Tim Barraclough of Imperial’s Department of Biological Sciences and the Royal Botanic Gardens, Kew, says:

“The idea that key evolutionary innovations drive an organism’s ability to diversify has been popular with evolutionary biologists for the past 10 years or so. But there’s a growing consensus that pinning the success of any group on a single innovation, such as insect fertilisation in the case of flowering plants, is too simplistic.”

“Instead, the diversity of flowering plant families is the result of interaction between existing biological traits and the environment in which the plant grows. Effectively biodiversity depends on being the right plant in the right place at the right time.”

“For example, grasses appear to be very successful because they have a suite of traits that allows them to thrive in cooler and drier environments. Their form of growth also makes them resistant to fire. But the same traits would not confer abundance and diversity in warmer, wetter environments.”

In a letter to Joseph Hooker, Kew’s first Director, in 1879, Darwin outlined his “abominable mystery” of flowering plants’ rapid diversification. Darwin described his own efforts to identify a single cause as “wretchedly poor”.

Subsequent attempts to understand this diversity have been revolutionized by the recent advent of molecular phylogenetics, which uses DNA sequence analysis to map evolutionary relationships. Using this technique, the team were able to compile the wealth of data from over 40 previous large-scale DNA studies on flowering plants into one super-tree.

“Even a decade ago, researchers said it was impossible to build a complete tree of flowering plant families. But recent advances in molecular phylogenetics have heralded a new era in analysing biodiversity,” explains Dr Vincent Savolainen of the Royal Botanic Gardens, Kew.

“Our examination of the top 10 major shifts in diversification, which include the grass family and the pea family, indicates they cannot easily be attributed to the action of a few key innovations.”

Dr Savolainen added: “The new super-tree will be a unique resource for future studies on plant diversity, ranging from biodiversity, gene evolution and ecological studies. It represents a major step towards the ’Tree of Life’, an international effort to recover the evolutionary relationships of all 1.5 million known species on Earth.”

Dr Tim Barraclough and Professor Mark Chase are Royal Society University Research Fellows.