CHAPEL HILL -- Working together, botanists from three universities have found what they believe is the first strong physical evidence that simple plants known as liverworts were the oldest land plants and predate more complex vascular plants that evolved millions of years later.

A report on their discovery appears in Tuesday’s (July 20) issue of the Proceedings of the National Academy of Sciences.

"This is rather exciting to us," said Dr. Patricia G. Gensel, professor of biology at the University of North Carolina at Chapel Hill’s College of Arts and Sciences. "We are pleased that we can demonstrate the existence of these kinds of plants this early in time. It fills yet another gap in our understanding of how plants got on the land and their early diversification."

Most studies that have been done in the past decade or so have suggested that liverworts were the most basal of all land plants, Gensel said.

"That means that they were more primitive than vascular plants and probably were in a sense ancestral to the rest of the plants," she said.

The UNC botanist and colleagues Drs. Linda E. Graham and Lee W. Wilcox of the University of Wisconsin and Dr. Martha E. Cook of Illinois State University think they have solved the mystery. Laboratory experiments they conducted on modern liverworts -- during which they broke down plant tissues -- resulted in bits and pieces of organic material. Those remnants were almost identical to fossilized plant fragments known to date back more than 400 million years.

"These little scraps were small tubular pieces and parts of what we call cuticle," Gensel said. "We produced modern ones resembling the fragmentary fossils by rotting them in soil for weeks and treating them chemically with heat and acid to decompose them. What we found was that the microscopic fossils we studied from sedimentary rock in northern New Brunswick and from earlier fossils uncovered in Wales were dead ringers for what we produced."

Some of the fossils were found by radioisotopic dating to extend back to the Devonian Period and some to the Silurian, some 410 to 415 million years ago. That the modern plant cuticle and other material Graham and Wilcox generated in their laboratory at Wisconsin were essentially identical to the ancient fossils Gensel specialized in demonstrated how close they were biochemically as well.

"There were a group of people who had said we could never know the early history of plants like liverworts because they don’t preserve well," the scientist said. "By not accepting that dogma, we were able to make this discovery, which has some interesting implications."

In Medieval times, people thought liverworts resembled liver and used them to treat liver ailments, Gensel said. The plants, which are related to mosses, look something like ribbons of flat baby lettuce with hairs on their undersides. They are pale to dark green and sometimes are mottled.

"Like lichens, liverworts are very important ecologically," Gensel said. "They have no direct commercial value that I know of, but they break down rock into soil, especially in environments not many other plants can live in.

"The other thing they do is contribute to sequestering carbon in their bodies, thus reducing the amount of carbon available to other organisms or to make carbon dioxide," she said. "Independent evidence suggests CO-2 levels decreased considerably during the Silurian-Devonian, which in turn affected climatic condition then -- and today."

In 1996, Gensel and colleagues in Virginia and Northern Ireland reported finding fossils of scorpions, millipedes and related arthropods dating back almost 400 million years. Those creatures, which predated dinosaurs and other reptiles by some 50 million to 100 million years, were the largest animals ever found on land up to that time in North America.

"Much of science is devoted to understanding and curing diseases, and that’s as it should be," Gensel said. "However, we also need to understand where living things have come from, which we can do by studying fossils. That gives us a better perspective on why the Earth and life are as they are today."

- 30 -

Note: Gensel can be reached at (919) 962-6937 or pgensel@bio.unc.edu

Contact: David Williamson, (919) 962-8596.