A research team from the University of Panama found the oldest fossil of an 18-million-year-old vine tree.
According to the researchers, who published their study in the journal PLOS ONE, the fossil provides evidence of a new species and is the oldest reliable example of a climbing woody vine known as a liana from the soapberry family.
In the study, the researchers made thin slices of the fossil, examined the arrangements and dimensions of tissues and water-conducting vessels under a microscope, and created a database of all the features.
They then studied the literature to see how these features matched up with the living and fossil records of plants. The researchers found that it does look like it's a fossil from the liana group, given the anatomical characteristics that are similar to species that live today.
Most trees and shrubs have water-conducting tissues (which transport water and minerals from roots to leaves) that are all roughly the same size; in vines, these conduits come in two sizes, big and small, which is exactly what the researchers discovered in the fossil.
"This is evidence that lianas have been creating unusual wood, even in their roots, as far back as 18 million years ago," said wood anatomist Joyce Chery, assistant research professor in the School of Integrative Plant Science, Plant Biology Section at the Panama University, in a report published on the university's website.
"Before this discovery, we knew almost nothing about when or where these lianas evolved or how rapidly they diversified," said co-author Nathan Jud, assistant professor of plant biology.
"The liana fossil has given us new insights, as it was among the plants that made it to North America long before the Great American Biotic Interchange when large animals moved between the continents some 3 million years ago," he added.
In future work, now that they can place this species of lianas to 18.5 million years ago, the researchers intend to continue their investigation of the evolutionary history and diversification of this family. They also plan to investigate how wood has evolved in this group of vines, including identifying the genes that contribute to lobe-shaped stems.