Charles Darwin, the founder of the theory of evolution, had already seen it: on distant islands you will find flowering plants with woody stems, which related species do not have on the continent. Darwin believed that this was the result of competition between individual plants for islands. In the battle for sunlight, it would be advantageous to reach a higher level than others, evolving from a herbaceous plant to a woody shrub and eventually a tree, as Darwin wrote a century and a half ago.
It’s a logical idea, but there’s no hard evidence for it, says Frederic Lins, head of research at Naturalis, the Leiden Institute for Biodiversity. Lens, who began his career at the Catholic University of Leuven, came to the conclusion after long research that there are more important factors that encourage plants to form wood. Especially drought. He recently published this finding with his Dutch and German colleagues, led by Alexander Zizka of the University of Marburg, in the professional journal PNAS.
Lins found the first evidence about ten years ago in the Canary Islands. “This is where my quarter fell. You can find the coarser flowering plants out there in the dry coastal regions, not in the higher, wetter areas,” he says. Lens now has a database of over a thousand types of carrots that turned wood after their herbaceous ancestors colonized the islands. This transition from herbal to woody has occurred independently no less than 175 times.
It is very common, says Lins, not only among the islanders but also the flower plants of the continents. There are about 300,000 flowering plants on Earth, called angiosperms or angiosperms. Of the 300,000 species, 180,000 are wood species. Think especially of flowering shrubs and trees, says Lins.
Seven hundred plants began to form wood again
The history of flower plants goes back about 145 million years. Their common ancestor was a woody plant. In the course of evolution, almost half of all species left wood formations behind. But the ability was preserved in almost all varieties; They all still have the genetic machinery for making wood, a tissue rich in lignin.
It seems easy for the factory to restart this device. Other than that, it won’t happen very often, says Lins. There are seven hundred independent cases worldwide of plants beginning to form wood again when their immediate ancestors were not. It is that 175 on the islands.”
Dehydration doesn’t have to be the only reason. What also plays a role in the islands is the generally mild climate with a long growing season. This gives the plant the advantage of flowering longer and living longer. “All factors that extend the life of a plant can enhance wood formation,” says Lins. This also applies to the fact that there are usually no large grazing animals on the islands that shorten the life of flower plants. But the common denominator in his database of species that have evolved into gracious shrubs and trees is drought.
Air bubbles in barrels
How does lignin help against dehydration? Lens: “The plant pulls water from the root into the leaf, against gravity, by creating negative pressure in its vessels. This is a poor system. During drought, air bubbles can form in those barrels, preventing water transfer. If the plant can’t resolve it, It will die. This is a common risk for all plants. But lignin appears to reduce this risk. We see that flower plants that have begun to form wood are more drought-resistant than their remaining herbaceous cousins.”
Lins says species that go back to wood remain a small minority of flowering plants, but that switching them is important to science. Climate change will cause plants in many regions to be exposed to drought stress more often. It will be important to monitor if this encourages flowering plants to form more lignin in the stem.”
A world where plant growth becomes more difficult anyway
It is not yet known exactly how the fetus’s genetic system works. This is the subject of a major research project that will now commence under the leadership of Naturalis and Leiden University. Lins believes that this is not only interesting from a scientific point of view, but also important for society. “Knowing this process, we can make food crops more drought-resistant. Because we’re on our way to a world where plant growth becomes more difficult anyway. We must do something to remain able to feed the world’s population.”
In addition, knowledge of wood composition can help make use of plant parts that are now discarded, such as the stems of tomato plants and other agricultural crops. With the right knowledge, we can turn it into biofuels.”
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