“While trees all tend to be the same shape, lianas are everywhere,” 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 anchor yourself in the trees you grow on,” said Marcelo Rodrigo Pace, botanist at the Universidad Nacional Autónoma de México and co-author of the study. “These lianas also have tendrils that allow them to grab pieces of stems and leaves and start growing.”
This adaptation is “purely mechanical, architectural”, he says. “It’s better than being slippery and cylindrical.”
The study considered two timescales: the life of an individual plant and a longer evolutionary width. Dr Chery and his colleagues found that in the early development of a single plant, when the liana is leafy, green, and small, the woody vines already have unusual tissue formation. The stem is star-shaped rather than circular; vascular bundles are scattered in the star body lobes and absent in the arcs. At later stages, this lobed structure can lead to more unusual growth patterns.
Over the course of evolutionary time, vines of different groups have developed various mechanisms for twisting their stems. The authors of the article found that the five different atypical forms found in mature liana stems trace their evolutionary history to a common disruption in the development of the young plant: the lobed stem.
“It’s exciting because it’s a step away from saying that it perfectly leads to understanding how lianas do what they do,” said Dr Schnitzer. While lianas share most of the characteristics with trees, such as wood production and prosperity under similar environmental conditions, the two types of plants invest differently in certain parts of their makeup. Lianas have more cells related to flexibility, while trees prioritize stiffness and strength. Both have cells responsible for stiffness and flexibility in different ratios.
“They have the same ingredients, but the proportion of those ingredients is distributed differently,” Dr. Chery said.
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