Speciation and Reticulation in the Polystichum Allotetraploids of the Costa Rican Cordillera Talamanca

Abstract. Polyploidy is a prominent force in the evolution of plant genomes, and the ferns are no exception. The genus Polystichum is particularly rich in polyploids, with 44% of the genus estimated to be polyploid. A waypoint between the Andean and Mayan centers of diversity, the Cordillera Talamanca of Costa Rica and Panama harbors three allotetraploid species of Polystichum, two of which are endemic. We leverage coding and non-coding DNA sequences from the chloroplast and nucleus to elucidate the allopolyploid origins of the three species. Consistent with, and building upon earlier works, we find evidence that the páramo tetraploid most recently named as Polystichum orbiculatum is derived from two distinct Andean progenitors, P. lilianiae is derived from two Mayan progenitors, and P. talamancanum is derived from one Andean and one Mayan progenitor. The Costa Rican polyploids incorporate the legacy of the Andean and Mayan regions into their genomes, forming new lineages with novel genotypes.