“Whereas trees all tend to be the same shape, lianas are all over the place,” said Stefan Schnitzer, a botanist at Marquette University who was not involved in the study.
These strange stem variations give the vines an advantage. “Being asymmetrical helps you to anchor in the trees you’re growing on,” said Marcelo Rodrigo Pace, a botanist at Universidad Nacional Autónoma de México and a co-author of the study. “These lianas also have tendrils that let them grab pieces of stems and leaves and start growing.”
This adaptation is “purely mechanical, architectural,” he said. “It’s better than being slippery and cylindrical.”
The study considered two scales of time: an individual plant’s life, and a longer, evolutionary breadth. Dr. Chery and her colleagues found that in a single plant’s early development, when the liana is leafy, green and small, woody vines already have an unusual tissue formation. The stem is star-shaped rather than circular; the vascular bundles are scattered in the lobes of the star-shaped body and absent in the arcs. At later stages, this lobed structure can lead to more unusual growth patterns.
Over evolutionary time, vines of different groups developed various mechanisms to contort their stems. The paper’s authors found that the five different atypical forms found in mature liana stems trace their evolutionary history back to a common disturbance to the young plant’s development: the lobed stem.
“This is exciting because it’s one step away from saying that this leads in perfectly to understanding how lianas do what they do,” Dr. Schnitzer said. While lianas share most characteristics with trees, like producing wood and thriving in similar environmental conditions, the two plant types invest differently in certain parts of their composition. Lianas have more cells related to being flexible, whereas trees prioritize being stiff and tough. Both have cells responsible for stiffness and flexibility in differing ratios.
“They have the same ingredients, but the proportion of those ingredients is distributed differently,” Dr. Chery said.