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Rapid Burst Of Flowering Plants Set Stage For Other Species

lanceolata is one of more than 70,000 species of flowering plants in
the rosid clade, which a new University of Florida study shows radiated
rapidly about 90 million years ago. This radiation set the stage for
the diversification of other plant and animal species. (Credit: Walter
Judd/University of Florida)
ScienceDaily (Feb. 19, 2009) — A new University of Florida study based on DNA 
analysis from living
flowering plants shows that the ancestors of most modern trees
diversified extremely rapidly 90 million years ago, ultimately leading
to the formation of forests that supported similar evolutionary bursts
in animals and other plants.
This burst of speciation over a 5-million-year span was one of three
major radiations of flowering plants, known as angiosperms. The study
focuses on diversification in the rosid clade, a group with a common
ancestor that now accounts for one-third of the world's flowering
plants. The forests that resulted provided the habitat that supported
later evolutionary diversifications for amphibians, ants, placental
mammals and ferns.
"Shortly after the angiosperm-dominated forests diversified, we see
this amazing diversification in other lineages, so they basically set
the habitat for all kinds of new things to arise," said Pamela Soltis,
study co-author and curator of molecular systematics and evolutionary
genetics at UF's Florida Museum of Natural History. "Associated with
some of the subsequent radiations is even the diversification of the
The study appearing online in next week's Proceedings of the
National Academy of Sciences is the first to show the evolutionary
relationships of these plants and provide evidence for their rapid
emergence and diversification.
Because the diversification happened so quickly, at least in
evolutionary terms, molecular methods were needed to sort out the
branches of the rosid clade's phylogenetic tree, a sort of family tree
based on genetic relationships. Only after sequencing many thousands of
DNA base pairs are genetic researchers able to tease apart the branches
and better understand how plant species evolved.
Often, when scientists discuss the rapid radiation of flowering
plants, they talk as if there had been one massive burst of early
diversification, said Doug Soltis, co-author and chair of UF's botany
"I think one thing that becomes very clear from our phylogenetic
trees when you look at them closely is that it's not just one big
explosion of species within the flowering plants," Doug Soltis said.
"There's a series of explosions."
The rosid clade's diversification is one of at least three bursts in
the early evolution of flowering plants. More than 300,000 species of
angiosperms exist, classified into an estimated 15,000 genera and more
than 400 families. Understanding how these plants are related is a
large undertaking that could help ecologists better understand which
species are more vulnerable to environmental factors such as climate
"We really need to know on a finer scale how these species are
related and on different parts of the planet how members of the clade
are related," Doug Soltis said. "That's where the action is going to be
in terms of how this clade responds to climate change. How members of
this large clade respond is really going to determine the fate of most
of the organisms on the planet."
The study's authors sequenced 25,000 base pairs of DNA and sampled a
broad range of 104 species from the rosid clade. Using a phylogenetic
tree to date the diversification of lineages requires the use of a
molecular clock, which calibrates the degree of change that has
occurred over time.
"You can assume that over time DNA sequences accumulate change, and
things that are more similar to each other in general would have
diverged from each other more recently than things that are more
different," Pam Soltis said.
But different genes have different rates of evolution, as do
different clades. To compensate, the study used algorithms that
accommodate the different rates. Rosid fossils selected by co-author
Steven Manchester, the museum's curator of paleobotany, were used to
help calibrate that clock by setting minimum ages for member species.
The study's first author is Hengchang Wang, who worked at the
Florida Museum as a post-doctoral fellow but is now with The Chinese
Academy of Science. Other authors include former post-doctoral fellows
Michael J. Moore from Oberlin College and Charles D. Bell from the
University of New Orleans. UF botany graduate students Samuel F.
Brockington and Maribeth Latvis, former UF undergraduate Roolse
Alexandre, and Charles C. Davis of Harvard University also contributed
to the study.
Journal reference:
        1. Hengchang Wang, Michael J. Moore, Pamela S. Soltis, Charles D.
Bell, Samuel F. Brockington, Roolse Alexandre, Charles C. Davis,
Maribeth Latvis, Steven R. Manchester, and Douglas E. Soltis. Rosid radiation 
and the rapid rise of angiosperm-dominated forests. Proceedings of the National 
Academy of Sciences, 2009; DOI: 10.1073/pnas.0813376106
Adapted from materials provided by University of Florida.
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