Fossil mystery: The ‘alien plant’ that defies classification

In 1969, paleobotanists identified fossilized leaves in eastern Utah belonging to the extinct species Othniophyton elongatum, a name that translates to “alien plant.” Initially, researchers speculated it might be part of the ginseng family. 

However, new discoveries have turned this assumption on its head. Recent fossil specimens reveal that this ancient plant is even stranger than previously thought, challenging how scientists classify extinct flora.

Alien plant with an unknown family

Steven Manchester, curator of paleobotany at the Florida Museum of Natural History, has spent years studying 47-million-year-old fossils from Utah. 

During a visit to the University of California, Berkeley, Manchester encountered an unusually well-preserved plant fossil from the same area as the original Othniophyton elongatum leaves. This fossil included leaves, fruits, and flowers attached to a woody stem – a rare find.

“This fossil is rare in having the twig with attached fruits and leaves. Usually those are found separately,” Manchester said.

Further analysis revealed that these fossils were from the same species as the 1969 find. However, the new evidence showed that Othniophyton elongatum didn’t fit within the ginseng family – or any other known plant family.

A plant with no living relatives

To uncover the origins of Othniophyton elongatum, Manchester and his colleagues compared the physical features of the fossils to over 400 modern plant families. Despite their extensive search, they couldn’t find a match.

“There are many things for which we have good evidence to put in a modern family or genus, but you can’t always shoehorn these things,” Manchester said.

This was the case with Othniophyton elongatum. Its peculiar combination of traits – including leaves, fruits, and flowers – defied placement in any known group. Even extinct families failed to provide a fit.

The research highlights a significant challenge in paleobotany: extinct plants from less than 65 million years ago are often assigned to modern families or genera. 

This practice can distort our understanding of ancient biodiversity, creating the false impression that prehistoric ecosystems were more similar to today’s than they actually were.

Strange fossils from an ancient lake

The fossils were discovered in the Green River Formation near the ghost town of Rainbow in eastern Utah. This formation, a massive inland lake system 47 million years ago, provided ideal conditions for preserving plants and animals in remarkable detail.

Low-oxygen sediments and volcanic ash slowed decomposition, resulting in the preservation of fish, reptiles, birds, and plants, including the fossils of Othniophyton elongatum. 

However, the original specimens collected in 1969 offered limited information. Researchers could only analyze the leaves, which resembled compound leaves commonly found in the ginseng family.

New fossils, though, painted a very different picture. Leaves attached directly to stems, rather than in a compound arrangement, ruled out the ginseng family. 

Additional features, including the plant’s fruits and flowers, ruled out other families like grasses and magnolias. Even with such detailed specimens, the team remained stumped.

“The two twigs we found show the same kind of leaf attached, but they’re not compound. They’re simple, which eliminates the possibility of it being anything in that family,” Manchester explained.

A new look at the alien plant

For years, the fossils sat in storage as researchers struggled to make sense of them. Then, new technology offered a breakthrough. The Florida Museum of Natural History established a microscopy workstation that allowed the team to examine the fossils in unprecedented detail.

Using a digital microscope with computer-enhanced shadow illumination, Manchester and his colleagues discovered features they had previously missed. The minute fruits revealed micro-impressions of their internal anatomy, including developing seeds.

“Normally we don’t expect to see that preserved in these types of fossils, but maybe we’ve been overlooking it because our equipment didn’t pick up that kind of topographic relief,” Manchester said.

One of the most striking aspects was the plant’s stamens, the male reproductive organs of its flowers. In most plants, stamens detach after fertilization, but in Othniophyton elongatum, they remain attached to the mature fruits – an unusual trait not seen in any modern plant.

“Usually, stamens will fall away as the fruit develops. And this thing seems unusual in that it’s retaining the stamens at the time it has mature fruits with seeds ready to disperse. We haven’t seen that in anything modern,” Manchester noted.

Shedding light on ancient ecosystems

The study’s lead author, Julian Correa-Narvaez, a doctoral student at the University of Florida, emphasized the importance of the discovery. “It’s important because it gives us a little bit of a clue about how these organisms were evolving and adapting in different places,” he said.

The diversity within plant families can be astonishing. For example, seemingly unrelated species like poison ivy, cashews, and mangoes belong to the same family, which contains over 800 species. However, with Othniophyton elongatum, scientists can only speculate about how much diversity has been lost to time.

Similar discoveries from the Green River Formation have unveiled other extinct plant groups, showing that it remains a rich site for paleobotanical mysteries. 

Significance of the alien plant

Digital tools like iDigBio, which allow researchers to access museum specimens remotely, are helping to unlock these mysteries and advance our understanding of plant evolution.

The discovery of Othniophyton elongatum not only expands our knowledge of extinct plants but also challenges assumptions about how ancient ecosystems functioned. 

Published in the journal Annals of Botany, this study serves as a reminder of how much remains to be discovered in the fossil record – and how evolving technology can illuminate the secrets of the distant past.

Image Credit: Florida Museum of Natural History photo by Jeff Gage

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