Taxonomy, Systematics, and Polyploidy in Xerochrysum, Coronidium and Helichrysum leucopsideum (Asteraceae; Gnaphaliaeae)

Abstract

<p>This thesis investigated the taxonomy, evolutionary relationships, ploidy-level and genome size in the Australian native paper daisies <i>Xerochrysum, Coronidium and Helichrysum leucopsideum</i>. The origins of the popular ornamental cultivars of <i>X. bracteatum</i>, grown worldwide since the late 1800s, and naturalised plants on the island of St Helena reputedly introduced by Napoleon Bonaparte, were investigated (Chapter 2). Our results revealed the cultivars to be hybrids between <i>X. bracteatum</i> and <i>X. macranthum</i> , with no evidence of <i>X. macranthum</i> in the ancestry of the St Helena island populations, supporting the hypothesis of their introduction by Napoleon.</p> <p>We addressed long-standing taxonomic confusion in the <i>X. bracteatum</i> species complex, and in <i>Coronidium sens. lat</i> ., with morphological and molecular data (Chapter 3 and Chapter 5). Using single nucleotide polymorphism data to corroborate morphological differences, we delimited 12 additional species of <i>Xerochrysum</i>, and four new species in <i>Coronidium sens. lat</i> . The data also supported the recircumscription of <i>X. bicolor</i> to include the recently described <i>X. halmaturorum</i> . The distribution, habitat and conservation status are discussed, and keys to genera and to all species are provided (Chapter 3 and Chapter 5).</p> <p>Evolutionary relationships in the study group were inferred with molecular data, and potential morphological synapomorphies identified (Chapter 4). The analyses supported the recognition of the new genus, <i>Leucozoma</i> T.L.Collins, for eight taxa previously included in <i>Coronidium</i>. Species-level relationships amongst most entities in <i>Coronidium</i> and <i>Leucozoma</i> were well-supported, though relationships amongst species of <i>Xerochrysum</i> were poorly resolved.</p> <p>We estimated genome sizes in the study group using flow cytometry, confirmed ploidy level using chromosome counts, and placed whole-genome duplication (WGD) events into a phylogenetic context (Chapter 6). Polyploidy was detected in seven species of <i>Xerochrysum</i> representing all major infrageneric clades, and no instances of WGD were detected in <i>Coronidium</i>, <i>Leucozoma</i> or <i>H. leucopsideum</i> . No larger clades have a polyploid ancestor, suggesting that WGD events did not play a role in the deeper diversification of <i>Xerochrysum</i>. Ploidy level provided additional support for the taxonomic recognition of morphologically distinct, tetraploid populations. </p>