Land plants, including mosses, ferns, and trees, represent some of the most structurally intricate photosynthetic organisms on the planet. Their evolutionary lineage, however, is closely connected to simpler ancestors—green algae that existed hundreds of millions of years ago. Among these, the Coleochaetophyceae group is noteworthy as a close relative of land plants that still thrives today. This freshwater algae group forms branching, disk-like structures, reminiscent of fundamental plant body components.
Interestingly, the closest living algal relatives of land plants, known as the Zygnematophyceae, are structurally simpler. This observation raises the possibility that the development of plant-like complexity occurred multiple times throughout evolutionary history. A recent study conducted by an international team of researchers, led by the University of Göttingen, utilized DNA analysis alongside fossil records to provide fresh insights into the Coleochaetophyceae.
The findings, published in Current Biology, indicate that this group of algae first emerged over 600 million years ago, predating the arrival of the earliest land plants. Within the Coleochaetophyceae, subgroups exist, including the genus Coleochaete, which has a lineage extending back more than 400 million years. Notably, more complex forms such as Coleochaete scutata only appeared approximately 65 million years ago, a relatively recent development in evolutionary terms.
Professor Jan de Vries from Göttingen University”s Institute of Microbiology and Genetics stated, “This tells us that we need to sample a broad diversity of ancient lineages to understand the evolution of complex traits such as body plans.” The fact that the closest living relatives—the Zygnematophyceae—exhibit much simpler structures suggests that the emergence of body complexity was not a singular evolutionary event; rather, it occurred repeatedly across different lineages at various times.
Upon analyzing the genetic sequences, researchers discovered that Coleochaetophyceae share numerous growth-regulating genes with land plants, including those related to cell division and essential plant hormones like cytokinin, which play a vital role in processes such as shoot and root development. However, there is no apparent single set of genes that explains why certain species develop into simple filamentous forms while others evolve into more sophisticated disk-shaped structures. This indicates that complexity relies not just on possessing the right genes but also on the timing and regulation of gene expression.
Maaike Bierenbroodspot, the study”s first author and also affiliated with Göttingen University, emphasized, “Our findings highlight that plant-like complexity is an ancient potential. This means that sometimes the genes were already present in the DNA until their functions were newly activated over the course of evolution, for instance, in algae and land plants.”
These revelations underscore the intricate evolutionary dynamics that have shaped the diversity of life forms we observe today.
