I have been working on ferns since 1980, starting at the Rijksherbarium Leiden, which is now morphed into the Botany section of the Naturalis Biodivesity Center. I have tackled a number of families and genera, always with the goal to find out how many (some would say, how few) species there really are. The main focus of my work has been on the Malesian part of the world (basically, Indonesia and surrounding countries), but I have also worked on the flora of China and Sri Lanka.
Equisetum has been around since the Jurrasic. What has contributed to this longevity? Satjarak et al. found evidence for eukaryotic microorganisms associated with Atacama Desert populations of Giant Equisetum, which may aid in its survival https://doi.org/10.1640/0002-8444-111.2.86