Jacob S. Suissa of the University of Tennessee has done a path-breaking study. Against deep-seated ideas more than 150 years old, he found a strong correlation between leaf arrangement and pattern of vascular bundles in ferns. His research indicates that the number of leaf ranks along a fern’s stem directly influences the number of vascular bundles within that stem. This findings sheds new light on anatomy of ferns. It also provides a window into the evolutionary mechanisms that shape and propel their development.
Suissa carried out his scientific research on this rare tobacco fern, or tobacco plants’ cousin, scientifically called Mickelia nicotianifolia. His results presented unambiguous cases of almost a one-to-one correspondence between leaf ranks and vascular bundles. For example, he noted that five vertical rows of leaves matched up with five vascular bundles in the stem. This discovery provides another way forward to investigate how overall leaf structure may lead to divergence of vascular patterns in ferns.
Methodology and Research Techniques
In order to come to these conclusions, Suissa employed cutting-edge imaging technology to pair with on-the-ground, field observations. He used a microCT scanner (basically a larger version of a CAT scanning machine) to see inside the stems and learn their internal structure. This hybrid approach of advanced machinery and skillful eyeballing has been absolutely key in unraveling the fern’s complex vascular architecture.
Suissa had the opportunity to sample 27 genera of ferns—about 30% of all fern species diversity. His body of work has underscored the need to synergize multiple types of research methods. Too frequently, we imagine research as involving cutting-edge instrumentation and heavy manipulative experimentation in the laboratory, yet natural history observations can lead to profoundly powerful findings. That’s true to an extent with this new work, too,” Suissa said.
Their research was a game-changing work in plant biology. It all came together in the form of a publication in the journal Current Biology. Beyond that, it serves as an artistic and personal reflection of Suissa’s expertise and enthusiasm for plant vasculature, a world he’s been exploring for almost ten years.
Insights into Evolutionary Patterns
Suissa’s observations lead her to make the discovery that with the addition of each new leaf, there is also the addition of a vascular bundle. He left his viewer with a sense of the fanciful pattern of vascular architecture seen inside the stems. “I noticed that the leaves of this fern are always produced on the dorsal or upper side of the fern stem and the vascular patterning in the stem looks quite whimsical, like a smiley face, with an elongated ventral bundle and several separated bundles at the top that were seemingly associated with the placement of leaves,” he explained.
Leaves have an important developmental influence on the evolution of vascular patterns among ferns. This detailed connection between leaf phyllotaxis and vascular patterning intensifies their appeal. At present, Suissa is engaged in research with his lab team to explore how the architecture of fern vasculature may have changed in the last 400 million years. Their goal is to produce a comprehensive, high-quality dataset investigating architectural patterns in more than 300 species from each fern family.
Educational Contributions
Along with his research, Suissa has had a long involvement in education that’s quite notable. In January 2025, he co-taught a Tropical Fern Biodiversity course in Costa Rica. He brought that knowledge and enthusiasm to the study of ferns at both the undergraduate and research levels. He serves in these important dual capacities—educator and researcher. This unique mix allows him to inspire a new generation of scientists to develop a more nuanced understanding of plant biology.
Suissa is currently pursuing a future direction of studying how ferns have evolved. He is passionate about combining traditional botanical understanding with modern scientific technology. “It started as a simple observation in the field, and most of the work was done with a razor blade and a camera, but I was able to integrate high-tech equipment like the microCT and quantitative evolutionary tools for projecting traits into the past to understand how they evolved,” he stated.