Ever since Klekowski: Testing a set of radical hypotheses revives the genetics of ferns and lycophytes

There have been three periods of significant discovery in the exploration of fern and lycophyte genetics. First, during the 1930s, Andersson‐Kottö conducted crossing studies on ferns. The publication of Manton's magnum opus on fern chromosomes in 1950 stimulated the second. The third emerged from Klekowski's 1973 American Journal of Botany publication that posed hypotheses linking breeding system dynamics and polyploid genetic architecture. Although Klekowski's assertions (predominant inbreeding and active polyploid genomes) were not supported, his hypotheses served as the impetus for improving our knowledge of the evolutionary mechanisms of ferns and lycophytes. It is now understood that (1) homosporous vascular plants are genetically diploid at high chromosome numbers and (2) both heterosporous and homosporous plants store and release genetic variation through a similar range of breeding systems. However, the seeming paradox of diploid genetic expression in homosporous vascular plants with high chromosome numbers remains unresolved. Ongoing and future research should include (1) more studies of gametophyte biology to elucidate the range and frequency of different breeding systems; (2) genomic analyses and new research on the mechanisms controlling bivalent formation to help discover how and why homosporous plant chromosomes appear so structurally stable; (3) considering whether the frequency of allopolyploidy in lineages can help explain why some are highly polyploid; and (4) chromosome painting studies to identify the dynamics of chromosome behavior in homosporous vascular plants. These open questions and continuing investigations demonstrate the longstanding impact of Klekowski's stimulating contribution.