Systematics of Eastern Australian Phebalium Vent. Sect. Phebalium (Rutaceae; Zanthoxyloideae)

Abstract

<p>The taxonomy of the Australian endemic <i>Phebalium</i> sect. <i>Phebalium</i> has not been addressed comprehensively for almost half a century. A well-corroborated species-level phylogeny with an updated taxonomy was lacking. This thesis aims to test the taxon boundaries of published and putative new taxa in the <i>Phebalium squamulosum</i> complex, one of the speciose complexes of the eastern Australian <i>Phebalium</i> sect. <i>Phebalium</i>, using multiple lines of evidence: phytochemistry, morphological and molecular data. Using these tested terminal taxa, the study also aims to estimate evolutionary relationships in <i>P. </i> sect. <i>Phebalium</i>. </p> <p>A pilot study allowed early investigation of morphology in the study group and addressed the urgent conservation assessment of an outlying population of <i>P. squamulosum</i> in South Australia. As a result, a new species, <i>P. calcicola</i> S.Dema & I.Telford was published (Chapter 2) and soon after it was listed as endangered.</p> <p>Building on the previous findings, the utility of the leaf essential oil terpene profiles as phenotypic characters for the delimitation of species was tested in the morphologically diverse <i>P. squamulosum</i> complex (Chapter 3). Employing gas-chromatography-mass spectrometry (GS-MS), the leaf terpene profile of 34 taxa of the <i>P. squamulosum</i> complex was analysed. The terpene profile corroborated the recognition of 20 species, either published or those delimited in the current study (Chapter 4). The characterisation of leaf terpene profiles of the <i>P. squamulosum</i> complex into three putative phytochemical groups (elemol/hedycaryol; squamulosone; monoterpene α-pinene dominated but without elemol/hedycaryol or squamulosone) was also novel. </p> <p>Morphological and molecular phenetics were used to test the hypothesis of the species limits in the <i>Phebalium squamulosum</i> complex. The morphological and SNP-based multivariate analyses corroborated the recognition of 15 new species, the reinstatement of 4 species, and the elevation of 4 subspecies to species. The molecular data also supported the species limits of published segregates. Reinstated species and species with change of rank have protologue and typification data presented. For the 15 new species, their diagnoses, descriptions, distributions, habitat information and conservation status are provided (Chapter 4).</p> <p>A reduced representation approach was used with SNP markers to reconstruct the species-level evolutionary relationships in <i>P. </i>sect. <i>Phebalium</i> (Chapter 5). Inferences based on all three phylogenetic methods (maximum likelihood, SVDquartets and maximum parsimony) and network analyses were congruent. A combination of phylogenetic and neighbour-net analyses resolved the monophyly of six south-western and 67 eastern Australian taxa of the current <i>P. </i>sect. <i>Phebalium</i>, most of which are recognised as species according to the explicit definition of such. The inter-specific relationships of most taxa in the eastern Australian clade of <i>P. </i>sect. <i>Phebalium</i> were elucidated.</p> <p>Our results supported the recently described sections, <i>P. </i>sect. <i>Microcybe</i> and <i>P. </i>sect. <i>Uniflorum</i>, as well as the eastern and south-western clades of <i>P. </i>sect. <i>Phebalium</i>. Our results also provided sound evidence for further division of the eastern Australian clade into nine sections. The formalisation of an infrageneric classification is deferred pending further and ongoing morphological characterisation of the clades. A distinct lineage with a unique combination of morphological attributes that merits a new monospecific section is described as <i>P. mirum</i> (Chapter 5).</p> <p>This study provided clues to the identity and affinity of various cultivated plants and cultivars of <i>Phebalium</i> (Chapters 4 & 5). The taxon boundaries and evolutionary relationships of only seven taxa could not be resolved. Potential research areas to address these taxa and limitations in the study are indicated (Chapter 6).</p>