PROVIDENCE, R.I. [Brown University] The cactus, stalwart of the desert, has quite a story to tell about the evolution of plant communities found the world over.
In a paper published in the early edition of the Proceedings of the National Academy of Sciences, Brown University biologists and colleagues have discovered that the rapid speciation of cacti occurred between 5 and 10 million years ago and coincided with species explosions by other succulent plant groups around the world. The researchers propose that a prolonged dry spell and possibly lower levels of atmospheric carbon dioxide during that time, known as the late Miocene, opened habitat that contributed to the rise of these plants and a broad vegetative makeover on Earth.
"The cacti, as a group, have been around for a while, but most of the species diversity that we see today was generated really recently," said Monica Arakaki, a postdoctoral researcher at Brown and the paper's lead author.
The Brown team and colleagues from Oberlin College and the University of Zurich, Switzerland, were interested primarily in dating the origins of the cacti (scientific name Cactaceae). The team sequenced the chloroplast genomes (the organelles inside plant leaves that engineer photosynthesis) for a dozen cacti and their relatives and combined their new genomic data with existing genomes to build a phylogeny, or evolutionary tree, for angiosperms, the genealogical line of flowering plants that represents roughly 90 percent of all plants worldwide. From there, the scientists deduced that Cactaceae first diverged from its angiosperm relatives roughly 35 million years ago but didn't engage in rapid speciation for at least another 25 million years.
"Cacti were actually present on the landscape for millions of years looking like cacti and acting like cacti before they began their major diversification," said Erika Edwards, assistant professor of biology in the Departme
|Contact: Richard Lewis|