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ItemPhylogeny and biogeography of Rhododendron section Vireya(University of Melbourne, 2004)Rhododendron L. is a large genus consisting of over 1000 species (Chamberlain et al. 1996). It extends from North America to Russia, and from Greenland to north-eastern Australia (Cowan 1949). The taxonomic history of the genus has been complex because of its size and diverse range of morphological variation; at present Rhododendron is divided into eight subgenera, which are further divided into sections and subsections. One of the most morphologically diverse groups of Rhododendron is section Vireya (Blume) Copel.f. of subgenus Rhododendron, the lepidote rhododendrons. Section Vireya has a unique distribution for the genus, being predominantly found throughout the Malesian Island Archipelago and extending into neighbouring areas, west to the Himalayas and east to north-eastern Australia and the Solomon Islands. The defining characteristics of section Vireya � the possession of seeds with tailed appendages at both ends, the twisting of capsule valves after opening, placentas that separate as thread-like structures from the central axis as the capsule opens � are subject to exceptions, although vireyas are easily distinguished from other rhododendrons by their general appearance. The alpha taxonomy of section Vireya is relatively well understood, although the evolutionary history of the group, the largest section in the genus, has not been studied. This thesis aims to bridge this gap in our knowledge. Phylogenetic analyses of three DNA regions, two chloroplast (psbA-trnH and trnT-trnL intergenic spacers) and one nuclear (Internal Transcribed Spacer), were conducted. The results of each analysis were generally congruent, with clades relating strongly to geographic areas. Section Vireya as currently circumscribed is shown to be not monophyletic, and only three of the seven subsections are resolved as monophyletic � Malayovireya Sleumer, Siphonovireya Sleumer and Pseudovireya Clarke. This is not surprising though, as the morphological characters traditionally used to circumscribe the subsections � leaf scale type and corolla shape � were shown to be homoplasious when mapped onto the summary molecular phylogeny, as were most characters, leaf scale type D being the only exception. An informal classification based on phylogenetic analyses is presented. Two subsections are recognised � Euvireya and Pseudovireya � and each is divided into two supersedes: Sahulensis and Euvireya, and Malesiana and Vaccinioides, respectively. Based on the other two monophyletic subsections of Sleumer (1966), two currently named subsections are retained as series in the new subsection Euvireya � Siphonovireya and Malayovireya. However, more information is required to delineate other series and test the proposed classification before the new ranks can be formalised. Since the 1860�s when Wallace recognised a biotic discontinuity between the Indo-Malay and Australian bird and mammal faunas, the Malesian Archipelago has held great interest for naturalists, and scientists alike. This study offered the opportunity to study the biogeographic history of the entire region, where most other biogeographic studies in the region have concentrated on taxa that are distributed in either the east or west. Cladistic biogeographic analysis of section Vireya, using paralogy-free subtrees, indicated an historic sequence. The summary area cladogram indicates that the Himalayas differentiated first, followed by the differentiation of areas (as an unresolved trichotomy) into eastern Malesia (Australia, New Guinea and Solomon Islands), western Malesia (Borneo, Java, Lesser Sunda Islands, Malay Peninsula, Moluccas, Philippines, Sulawesi and Sumatra) and Taiwan and north Vietnam/south China. Further differentiation took place within these three regions, although the order of vicariance events is not well resolved. Based on this, several hypotheses for the evolution and age of vireyas are proposed: one suggesting vireyas are a young group, the other suggesting the opposite, that they are old.