Widespread cytonuclear discordance in narrow-leaved cattail (Typha angustifolia) does not explain the dominance of its invasive hybrid (Typha x glauca)

Cattails (Typha spp.) are common and abundant in wetlands around the world, and can be invasive. Typha latifolia and T. angustifolia are two widely distributed species that in North America produce the invasive hybrid T. x glauca, of which T. angustifolia is the maternal parent. A recent study identified polyphyly in T. angustifolia resulting from core and divergent chloroplast DNA (cpDNA) lineages. We used a combination of chloroplast and nuclear genetic data to test two hypotheses: (1) T. angustifolia with the divergent cpDNA lineage represents a cryptic species and (2) divergent cpDNA T. angustifolia haplotypes predominate in areas where T. x glauca is invasive. Our data reject the hypothesis of a cryptic species, and we suggest that the divergent lineage arose in T. angustifolia following historical hybridization and introgression. Typha x glauca may therefore be a three-way hybrid involving T. latifolia, T. angustifolia, and an introgressed cpDNA lineage from an unidentified congener. The divergent cpDNA T. angustifolia haplotype is widespread across areas where T. x glauca is invasive, but is also found in areas where T. x glauca is maintained at very low frequencies; therefore, cpDNA lineages cannot be the sole explanation for T. x glauca invasiveness.