Tracing the origins of hybrids through history: monstrous cultivars and Napoléon Bonaparte's exiled paper daisies (Asteraceae; Gnaphalieae)

Abstract

<p>Golden everlasting paper daisies (<i>Xerochrysum, Gnaphalieae, Asteraceae</i>) were some of the earliest Australian native plants to be cultivated in Europe. Reputedly a favourite of Napoléon Bonaparte and Empress Joséphine, <i>X. bracteatum</i> is thought to have been introduced to the island of St Helena in the South Atlantic during Napoléon's exile there. Colourful cultivars were developed in the 1850s, and there is a widely held view that these were produced by crossing <i>Xerochrysum</i> with African or Asian <i>Helichrysum</i> spp. Recent molecular phylogenetic analyses and subtribal classification of Gnaphalieae cast doubt on this idea. Using single-nucleotide polymorphism (SNP) data, we looked for evidence of gene flow between modern cultivars, naturalized paper daisies from St Helena and four <i>Xerochrysum</i> spp. recorded in Europe in the 1800s. There was strong support for gene flow between cultivars and <i>X. macranthum</i>. Paper daisies from St Helena were genotypically congruent with <i>X. bracteatum</i> and showed no indications of ancestry from other species or from the cultivars, consistent with the continuous occurrence of naturalized paper daisies introduced by Joséphine and Napoléon. We also present new evidence for the origin of colourful <i>Xerochrysum</i> cultivars and hybridization of congeners in Europe from Australian collections.</p>