The plant revolution

Suzanne Leclercq brings paleobotany into the modern age. More than just a discipline, it's a whole vision of science that's been dusted off through its practices, methods and rigor. Several milestones along the way mark revolutions in our understanding of our past. In particular, she describes one of the first forests dating from the Middle Devonian period. She literally dissected fossil plants, documenting them in minute detail. Unprecedented methods and techniques enabled her to do this, and are now part of her precious legacy. But perhaps the most remarkable story is that of a woman's scientific breakthrough into a world still jealously guarded by men.

 

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t was anthropologist Charles Fraipont, son of Julien Fraipont, who first noticed Suzanne Leclercq's exceptional skills. In 1923, she became his assistant, working primarily on paleoanthropological questions. we were still in our infancy when it came to understanding the origins of mankind," recalls Cyrille Prestianni, paleobotanist at the Institut des Sciences Naturelles in Brussels. It was a time when a lot of comparative studies were still being carried out, particularly with apes, on which Suzanne Leclercq was working for Charles Fraipont While Fraipont opened the doors to the academic world, it was paleontologist Armand Renier who steered her towards paleobotany. For the young researcher, this was a revelation that would earn her a place in the pantheon of this discipline.

Plants as new witnesses to our origins

The 1920s saw the start of a veritable revolution in paleontology. Tons of coal balls - balls of calcium carbonate that had precipitated out of the coal beds, trapping plants in their original form - were being extracted from the coal beds, which were now being extensively exploited by industrialists. Without these shells, they would have been transformed into coal like the rest of the plants accumulated at the same time, this highly evolved material whose components are no longer recognizable. these plants date back to the Carboniferous period," points out Cyrille Prestianni. This means that they have been anatomically preserved for over 300 million years."" Annick Anceau, geologist and mineralogist at ULiège, secretary of the Geological Society of Belgium and editor of the journal Geologica Belgica, continues: "Usually , fossil plants are crushed in sediments. Here, however, they have been preserved in three dimensions. This means we've been able to study their entire structure and go a long way towards understanding them, cell by cell."

Armand Renier set Suzanne Leclercq on the trail of these coal balls. In 1925, she published an anatomical inventory of the plants found in the coal balls of the Bouxharmont layer at the Wérister colliery in Belgium. Just a few months ago, an Argentinian researcher asked for a copy. For this first research project, Suzanne Leclercq already had all the qualities that would make her famous: dexterity, meticulousness, seriousness and a strong critical sense. What's more, she brought the study of fossils into the modern age. In the ^19th century, scientists were collecting information. Collected fossils were considered objects, useful for dating the earth's layers. Suzanne Leclercq, among other botanists, found herself at a turning point, gradually moving away from this stratigraphic approach to look at fossils from a botanist's point of view. these researchers wanted to understand how these plants lived, and in what environment they evolved," says Cyrille Prestianni. In other words, they wanted to understand ancient plants for what they were. From this biological constraint emerged the reconstruction of a real puzzle. When a plant fossils, it is often fragmented. The trunk is on one side, the roots on the other, the leaves a little further away... The stratigraphic approach was content to number fossils. The biological approach aims to put the pieces together

This 1925 publication remains an inventory. It was not until later work, notably that of Muriel Fairon-Demaret, another female paleobotanist from Liège, that real botanical reconstructions emerged. Nevertheless, the turning point has been reached, and the scientist from Liège is following a new path. She studied thousands of coal balls over a period of ten years, which enabled her, for the time, to more or less exhaust the subject of Belgian Carboniferous plants. This did not, however, enable her to understand the origin of plants on Earth.

The Carboniferous wall

Throughout the ^19th century, the Carboniferous was seen as an antediluvian world, with the oldest terrestrial environments. Of course, older periods are known, notably the Devonian. But most of what we know about it comes from marine environments. 

All the work devoted to the Carboniferous, which continued until the 1970s, generated a wealth of knowledge on the subject. Gradually, scientists realized that they were looking at an already complex world of highly evolved forests and land animals. This diversified life spread across the earth's surface must have appeared even earlier.

Then, in 1920, scientists in England discovered the Rhynie flora. A siliceous hot spring had preserved a snapshot of the Lower Devonian environment (419.2 to 393.3 million years ago). you could see plants from the past like you'd never seen them before," says Cyrille Prestianni. You realize that they're very different from the ones we know. They're simple, primitive, and still impossible to compare with more recent species. Some keys are missing. But to realize that the Devonian was so different is a real shock to the international community. We're barely half a century after Charles Darwin's theories Between the ferns of the early Devonian and the trees of the Carboniferous, over just a few tens of millions of years, something happened to land plants. Something that was still shrouded in the thick mists of an all-too-distant past. For these researchers, trying to understand the origin of plants, a breach seemed to be opening in the Carboniferous wall. The need to discover the Devonian was becoming obvious.

Going back further in time

The Devonian is an unrecognizable world. The Earth was divided into three major continental masses. Most of the land masses formed an immense continent, Gondwana, which then occupied the South Pole. Higher up, another large mass, Laurussia, comprised the future Europe and North America. Belgium is now in the southern hemisphere. It was very hot, as was the rest of the planet, with little climatic stratification. Once again, Armand Renier's journey continues. He sensed the importance of studying the Devonian and commissioned two researchers. François Stockmans in Brussels and Suzanne Leclercq in Liège. Leclercq perpetuated a museum-like, stratigraphic approach to fossils. He collected and described hundreds of fossils, and produced an extensive inventory of past Belgian flora. Suzanne Leclercq, on the other hand, would sometimes devote several years to a single organism, studying it as a living being. This ambition to understand such plants in minute detail came up against a major difficulty: fossils are crushed between layers of rock and are anatomically far less preserved than in coal balls. But Suzanne Leclercq's perseverance enabled her to develop a genuine method of fossil dissection, which still bears her name today, and which is a precise hammer and triangular needle process. It may sound simple, but it's the result of an unprecedented meticulousness.

What she unearths from the past and reveals to her contemporaries is prodigious. Eviostachya, Rhacophyton, Calamophyton- these are just a few of the somewhat barbaric names for a primitive sphenophyte, an ancient fern and, finally, a new and as yet totally unknown tree. During a series of searches in the Goé area, she discovered Pseudosporochnus , the oldest forest known at the time, dating back to the Middle Devonian (393.3 to 382.7 million years ago). other forests have been discovered since then," admits Cyrille Prestianni. But this remains one of the oldest. And it's a major work, because it completely changes our vision of plants and paleobotany. The reign imagined for the Devonian was that of ferns and herbaceous plants. And what it shows is that by the Middle Devonian, we already have trees and highly structured environments."

She continues to study Middle Devonian plants. From a resolutely modern perspective, she maintained an international network, focusing on the USA, England, France and India. Her correspondence was extensive, and the trust placed in her through the submission of numerous specimens provided an abundance of material for the university's collections. By the end of his career, his international reputation seemed boundless. As is often the case, researchers, particularly American ones, submitted plants to her. She was unable to solve the riddles hidden in one of them. Today, Cyrille Prestianni is studying it. But of another, Psilophyton dawsonii, she produced an incredibly precise and well-written description. "What she identifies is nothing less than the archetypal terrestrial plant. In other words, when we establish a phylogeny of living beings, we start with a primitive organism from which we can polarize the sequence of characters of its various evolutions. And even today, when we carry out a phylogeny of terrestrial flora, we start from this plant described by Suzanne Leclercq in 1975, among others." 

A multi-faceted heritage

Everyone in paleobotany knew Suzanne Leclercq, and vice versa. Whenever a researcher wanted to study a particular subject, her advice was sought. And in many ways, like her subject, it's possible to draw up a complex phylogeny of Suzanne Leclercq's legacy. First of all, she created the Chair of Paleobotany at the University of Liège, and for Belgium. Two people succeeded her in two distinct branches. Firstly, Muriel Fairon-Demaret, who continued her work on Pseudosporochnus, and who continues to be one of the leaders in the understanding of Devonian forests and continental plants. Towards the end of her career, Suzanne Leclercq became interested in spores as a botanist. In the course of discussions, she realized that they could be valuable stratigraphic tools. She hired Maurice Streel to help her along the way. The result was a stratigraphic scale created from scratch using spores, solving the mysteries pursued by whole generations of geologists in their quest for an ever finer understanding of rock succession.

Suzanne Leclercq also leaves behind an innovative know-how. The technique she developed for clearing plants was unique in that it used triangular needles, but it was above all the way she approached the plant and cleared it without destroying it that was a formidable innovation. it was like lace," admires Annick Anceau. Scientists from all over the world came to Liège to learn her technique. All these researchers took this know-how with them. In the USA, for example, where there's a great tradition of the history of science, it's cited in numerous works."

She also borrowed a method for preparing slides from an English researcher, John Walton, and applied it to the study of coal balls. "Traditionally, to study fossils under the microscope, we make sequential cuts, which we polish and glue onto a glass plate. Each time, a few millimetres of the fossil are lost. Walton's technique also involves polishing, which is then immersed in hydrochloric acid. The acid attacks the calcium carbonate without degrading the organic matter, which is then trapped in a film of cellulose acetate. Instead of having one cut every three millimeters, we have thirty. This means we can observe all the plant's strata. The accumulation of two-dimensional sections can give us an idea of the plant in three dimensions. From that point on, we understand everything. This is how she studied most of her plants. Her slides were scanned, and those are still the ones we study today."

A pioneering female figure 

Those who knew Suzanne Leclercq will take pleasure in recalling the exacting standards and honesty of a person who was strict, but grateful for everyone's hard work. Brilliant, she was also a strong personality, probably necessary to break into a man's world in the 1930s. she was certainly fortunate to meet two men who recognized her scientific qualities and allied themselves with her," adds Annick Anceau. But that doesn't take anything away from her merit. After all, she was the first woman to be awarded the agrégation de l'enseignement supérieur in Belgium, in 1931, and to become a full professor at the University of Liège, in 1937. It's important to remember that women did not yet have the right to vote when Suzanne Leclercq became one of the most brilliant scientists in her department, and one of the most influential in the world. She was a very modern person, a feminist before her time, a public figure who traveled a lot, and who was also very involved in the cultural life of Liège."

View Suzanne Leclercq's biography 

Cyrille Prestianni

Cyrille Prestianni joined ULiège in 2000. He began studying biology, and after applying for a degree, switched to plant biology. Thanks to Muriel Fairon-Demaret, he developed a taste for plant paleontology and asked permission to write his dissertation in this department. In 2004, he presented his research on a Devonian seed plant. His thesis, supervised by Philippe Gerrienne, enabled him to study Devonian spermatophytes in greater depth. Between 2009 and 2010, he spent a post-doctoral year at the Montpellier paleobotany laboratory. On his return to Belgium, he joined the Royal Belgian Institute of Sciences in Brussels as a paleobotanist researcher. At first, he was attached to the collections, before migrating from contract to contract, where he studied a wide range of subjects, although, as a good Liège man, he remained attached to the Devonian and to ULiège.