Origin of subgenomes in the circumboreal, allopolyploid, carnivorous plant Drosera anglica

The parentage of the widespread allopolyploid Drosera anglica, a member of the carnivorous sundew genus, remains uncertain despite over 100 years of morphological, cytological, and, more recently, molecular study.

Using transcriptomic and genomic data from 12 species of Drosera sect. Drosera, including four D. anglica populations and a population sometimes identified as disjunct D. intermedia, we assembled genes in HybPiper and phased sequences in HybPhaser. We estimated species relationships with phylogenetic and pairwise genetic distance methods and ploidy with heterozygosity and flow cytometry measurements. Additionally, we expanded represented taxa by analyzing new and previously published rbcL sequences.

Sequences from phased subgenomes of D. anglica were highly similar to D. rotundifolia (99.60-99.80%) and D. linearis (99.79-99.95%) and showed no evidence of multiple origins despite sampling across North America, Europe, and Hawaii. Additionally, the disjunct D. intermedia from Idaho had been misidentified and is D. anglica. Sequences from the nuclear ribosomal region and rbcL of D. anglica were nearly identical to D. linearis despite their chromosomes mispairing during meiosis and counter to interpretations of limited Sanger sequencing. Drosera anglica is intermediate between its parental lineages in leaf shape and microhabitat; however, across D. sect. Drosera, neither leaf shape nor biogeographic distribution was a reliable indicator of phylogenetic relationships.

Drosera anglica arose from allopolyploidy between the D. linearis lineage, representing the plastid and dominant ribosomal donor, and the D. rotundifolia lineage. Our study demonstrates the importance of taxon sampling and careful examination of complex phylogenomic data and presents an exemplar of analyzing allopolyploid relationships.