Order-level fern plastome phylogenomics: new insights from Hymenophyllales

PREMISE OF THE STUDY: Filmy ferns (Hymenophyllales) are a highly specialized lineage, having mesophyll one cell layer thick and inhabiting particularly shaded and humid environments. The phylogenetic placement of Hymenophyllales has been inconclusive, and while over 87 whole fern plastomes have been published, none was from Hymenophyllales. To better understand the evolutionary history of filmy ferns, we sequenced the first complete plastome for this order. METHODS: We compiled a plastome phylogenomic dataset encompassing all eleven fern orders, and reconstructed phylogenies using different data types (nucleotides, codons, and amino acids) and partition schemes (codon positions and loci). To infer the evolution of fern plastome organization, we coded plastomic features, including inversions, inverted repeat boundary shifts, gene losses, and tRNA anticodon sequences as characters, and reconstructed the ancestral states for these characters. KEY RESULTS: We discovered a suite of novel, Hy...