Reconstructing Dryopteris “semicristata” (Dryopteridaceae): Molecular profiles of tetraploids verify their undiscovered diploid ancestor

Abstract

• Premise of the study: Discovering missing ancestors is essential to understanding the evolutionary history of biodiversity on Earth. Evidence from extinct species can provide links for reconstructing intricate patterns of reticulate relationships among extant descendents. When fossils are unavailable and other evidence yields competing hypotheses to explain species ancestry, data from proteins and DNA can help resolve conflicts and generate novel perspectives. The identity of a parent shared by two tetraploid species in the cosmopolitan fern genus Dryopteris has remained elusive for more than 50 years. Based on available data, four hypotheses were developed previously, each providing a different resolution to this uncertainty.

• Methods: New molecular evidence from studies of isozymes and restriction site analysis of chloroplast DNA tested the competing hypotheses about the diploid ancestors of these two extant Dryopteris polyploids.

• Key results: The results falsify two of the hypotheses, resolve the uncertainty in the third, and support the fourth.

• Conclusions: Our data validate the prior existence of Dryopteris “semicristata,” which was proposed 38 years ago as a diploid progenitor of the allotetraploids D. cristata and D. carthusiana but has never been collected. After developing a phylogeny using the new molecular data, we describe a plausible morphology for D. “semicristata” by extrapolating likely character states from related extant species.