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In the rainforests of western Panama, plant biologist Jim Dalling found a tree fern whose six-foot-long, dying leaves curled to the ground, encircling the plant like a skirt.
“I was trying to move these things out of the way, and in the process I noticed that they were rooted in the ground,” Dr Dalling said. The University of Illinois professor and forest ecologist was looking for completely unrelated plants.
The remains of the fern’s leaves were brown, wilted, and apparently dead (though the base was still attached to the tree fern’s trunk). How could roots grow in a lifeless plant? he wondered.
“I just couldn’t believe what I was seeing,” Dr. Dalling said.
Further research revealed that this tree fern, known as Cyathea rojasiana, changes the interior of its dead or dying leaves. The remains of xylem and phloem (the tubes that transport water, sugars, and nutrients throughout the living leaves) somehow become roots.
The tips of these leaves, called “zombie leaves,” sprout new thin roots that penetrate the soil, said Dr. Dalling, co-author of a study published in the journal Ecology in January. said.
In the process of changing the leaf midrib, the plant undergoes growth of new vascular tissue to avoid decay until the rest of the leaf dies.
“This is completely unknown in any other factory in the world,” he said.
“Normally the vascular tissue is in the leaf, and that’s it,” says Robin Moran, a fern expert and curator emeritus of the New York Botanical Garden in the Bronx. But in this species, after the rest of the leaves die, “they differentiate and multiply. We don’t know how that happens.”
“I’ve never seen anything like it,” added Dr. Moran, who was not involved in the paper.
This tree fern is found in moist areas of the Fortuna Forest Preserve, which receives more than 6 feet of rain per year. Rain leaches the sandy volcanic soil, releasing nitrogen and phosphorus. Researchers believe the fern’s adaptation allows it to tap into pockets of nutrients in nearby topsoil that it wouldn’t have access to otherwise.
Many plants are known for their almost limitless adaptability, and other species can produce new roots from living leaves. Notable examples include the American native walking fern (Asplenium rhizophyllum), which uses this technique to spread across moss-covered rocks.
But Eddie Watkins, a Colgate University professor and fern expert who was not involved in the study, says the tree fern’s “zombie leaves,” or leaf roots, are a great way to recycle dying tissue. He said it was the first known example.
Dr. Watkins suggested that plants most likely conserve energy by converting existing leaf material into roots. It could help fight “competition for nutrients” in parts of the rainforest.
Heavy rains and poor soil form a unique group of plants, including conifers known as podocarpus, Greek for “fruit with legs” (after the stalked appearance of another species in the same genus) . This evergreen grows strange bulbs everywhere, including on the trunks of surrounding trees. It was conifers that Dr. Dalling first started rummaging through.
“It was pure coincidence that we were digging at the base of these tree ferns,” he said.
Dr. Dalling examined dozens of these ferns and discovered that each one grew roots from “zombie fronds.” However, the outbreak of the coronavirus pandemic interrupted his work and forced him to leave Panama with his wife and dog and return to Illinois in February 2020.
Two years later he returned. Dr Dalling and his colleagues dug out the roots from the leaves of three plants, placed them in pots and added fertilizer containing chemically labeled nitrogen. After a month, they examined the new leaves at the top of the fern and found that nitrogen was indeed being taken up by the plant, confirming that these roots were actively transporting water and nutrients. it was done.
Much remains unknown, including essentially all the developmental and biochemical secrets of how this particular tree fern grows. accomplish such transformative feats. The discovery speaks to the importance of taking time to study and appreciate the natural world, Watkins said, adding that this type of exploration is becoming less frequent and harder to fund.
“When you stop and look at the organisms, you realize there are some really new and amazing things out there,” Dr. Watkins said. “There are stories to be told that we have yet to discover.”
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