New research scheduled to appear as the journal Nature’s cover story on February 1 concludes that ferns and horsetails are not -- as currently believed -- lower, transitional evolutionary grades between mosses and flowering plants. In fact, ferns and horsetails, together, are the closest living relatives to seed plants.

"Today's systematists are using genomic tools to re-write the textbooks on animal and plant evolution," says James Rodman, program director in NSF's division of environmental biology, which funded the research. "This research is the latest major rearrangement of the plant tree of life. It will encourage others to explore ferns as model organisms for basic ecological and physiological studies."

The research calls for rethinking the "family tree" of green plants, according to scientists. Also, it uncovers a research shortcoming: All main plant model organisms used for research (such as Arabidopsis, which became the first plant to have all its genes sequenced) are recently evolved flowering plants.

This limitation could compromise scientific research. Models in the newly identified fern and horsetail lineage are needed to round out the study of plant development and evolution. This could help scientists fight invasive species, engineer genetic traits, develop better crops and prospect the botanical world for medicines.

The new research uses morphological and DNA sequence data to show that horsetails and ferns make up one genetically related group, which evolved in parallel to the other major genetically related group made up of seed plants and including flowering plants.

"Our discovery that 99 percent of vascular plants fall into two major lineages with separate evolutionary histories dating back 400 million years. It will likely have a significant impact on several disciplines, including ecology, evolutionary biology and plant developmental genetics," said Kathleen Pryer, lead author of the paper and assistant curator in botany at The Field Museum in Chicago. "Viewing these two genetically related groups as contemporaneous and ancient lineages will likely also have profound consequences on our understanding of how terrestrial ecosystems and landscapes evolved."

The work of Pryer and her colleagues builds on the Deep Green project, a collaboration of researchers dedicated to uncovering the evolution of and interrelation of all green plants. In 1999, Deep Green reported at an international botanical conference that DNA analysis indicates that all green plants -- from the tiniest single-celled algae to the grandest redwoods -- descended from a common single-celled ancestor a billion years ago. Green plants, which include some 500,000 species, are among the best-documented groups in the tree of life.

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