‘Zombie’ fern takes unusual roots in forest – 02/28/2024 – Science

In the rainforests of western Panama, plant biologist Jim Dalling stumbled upon some ferns with 6-foot-long fronds that curled toward the ground as they died, surrounding the plant like a skirt.

“I was trying to move these things out of the way, and then in the process I realized they were rooted to the ground,” Dalling said. A professor and forest ecologist at the University of Illinois, he was looking for another plant.

The remains of the fern’s leaves were brown and withered — dead, apparently (although they were still attached to the base of the trunk). He asked himself: how could lifeless plant matter be endowed with roots?

“I really couldn’t believe what I was seeing,” Dalling said.

Additional studies revealed that this fern, known as Cyathea rojasiana, transforms the inner part of its dead or dying leaves. The remains of xylem and phloem — tubes that carry water, sugars and nutrients throughout the living leaf — somehow become a root.

From the tips of these “zombie leaves” sprout new, thin roots that penetrate the soil, said Dalling, co-author of a study describing the findings published in January in the journal Ecology.

In the process of transmuting the central nerve of the leaf, the plant undergoes a proliferation of new vascular tissue — and avoids rotting while the rest of the leaf dries.

“This is completely unknown in any other plant in the world,” he said.

“Normally, the vascular tissue is deposited in the leaf and that’s it,” said Robbin Moran, a fern expert and curator emeritus at the New York Botanical Garden in the Bronx. But with this species, after the rest of the leaf dies, “it’s differentiating, proliferating. I don’t know how that happens.”

“I’ve never seen anything like it,” added Moran, who was not involved in the article.

This fern is found in a waterlogged area of ​​the Fortuna Forest Reserve, which receives more than 20 feet of rain per year. Rain leaches the sandy, volcanic soil, draining it of nitrogen and phosphorus. The researchers say they believe the fern’s adaptation allows it to access pockets of nutrients in nearby topsoil that it could not otherwise access.

Many plants are known for their almost limitless ability to adapt, and other species can produce new roots from living leaves. Notable examples include the walking fern (Asplenium rhizophyllum), native to the United States, which spreads over mossy rocks using this technique.

But this fern’s “zombie fronds” represent the first known example of repurposing dying tissue, said Eddie Watkins, a professor and fern expert at Colgate University who was not part of the study.

By turning existing leaf material into roots, the plant likely saves energy, Watkins suggested. This could help her in the “battle for nutrients” in her part of the rainforest.

Heavy rains and poor soils provide a unique collection of plants, including a pine tree known as Podocarpus, from the Greek for “stalked fruit,” and which spreads strange bulbous roots far and wide. It was this pine that prompted Dalling to search the vegetation in the first place.

“It was pure luck that we were touching the base of these ferns,” he said.

Dalling inspected dozens of these ferns, discovering that each one grew roots from its “zombie fronds.” But his work was interrupted by the onset of the coronavirus pandemic, forcing him to leave Panama with his wife and dog and return to Illinois in February 2020.

Two years later, he returned. With colleagues, Dalling dug up leaf roots from three individual plants, placed them in pots and added a chemically labeled nitrogen fertilizer.

A month later, they examined new fronds at the top of the fern and discovered that nitrogen was indeed being incorporated into the plant — confirming that these roots were actively transporting water and nutrients.

However, it is not yet known how this fern accomplishes such a transformational feat.

The discovery, according to Watkins, shows the importance of taking time to study and appreciate the natural world — and this type of exploration has become less frequent and difficult to finance.

“If you stop and look at the organism, there are really new and interesting things out there,” Watkins said. “There are stories to be told that we haven’t discovered yet.”