Science|How Woody Vines Do the Twist

Trilobites

Slowly, scientists are learning how lianas quickly climb.

Credit…Anton Sorokin/Alamy

Wood is typically thought of as stiff and rigid, but some wood, in the race upward to access the best sunlight, twists. Lianas, or woody vines, are concentrated in tropical forests; they possess a narrow stem that lets them climb to the top of the canopy, more than 100 feet above the ground, as quickly as possible by twisting their way around tree trunks. Basking in the sun at the top, these vines flower, fruit and lay out new leaves as they photosynthesize.

But the number of lianas is increasing in tropical forests relative to trees, and their overabundance can hamper a forest’s ability to store carbon, so botanists are eager to learn as much about these plants as they can.

“We understand a lot about their ecology, but we don’t understand how these diverse and strange wood forms evolved,” said Joyce Chery, a botanist at Cornell, and the lead author of a study published earlier this year in the journal Current Biology.

In early 2017, as a graduate student, Dr. Chery visited the Smithsonian Tropical Research Institute in Panama, where she collected cross-section samples of various species of Paullinia, a lineage of liana. Those samples are now part of the herbaria at the University of California, Berkeley, and the University of Panama.

Dr. Chery extracted DNA from the leaves and analyzed the molecular sequence of each sample, and of similar samples stored at herbaria at the University of Panama, Universidad Nacional Autónoma de México and the Smithsonian Institution. She also studied the configuration of cells in 148 samples of cross-sections of the stems.


Image

Credit…Luis Acosta/Agence France-Presse — Getty Images

From this analysis, Dr. Chery and the co-authors on the recent paper identified five patterns of stem growth, ranging from circular to lobed, to star-shaped cross-sections.

The driving force behind each of these patterns is a bundle of cells behind the bark called the vascular cambium. To survive, a woody vine must be both strong and flexible — variant shapes allow woody vines to make the twists and turns they need to be successful in the tropics. Their sugar- and water-conducting cells are positioned in

Read More