Molecular systematics, biogeography, and mycorrhizal associations in the Acianthinae (Orchidaceae), with a focus on the genus Corybas

The orchid subtribe Acianthinae, containing roughly 170 species in five genera, consists of almost exclusively terrestrial, diminutive species, most of which seem to be pollinated by small flies. The group is poorly studied, and presents unique opportunities for evolutionary studies. While the vegetative features are fairly uniform within the group, floral diversity is quite substantial, especially in the large genus Corybas. Though part of the primarily Australian Diurideae, this particular subtribe has a remarkably wide range spanning much of Australasia and the Malay Archipelago, into mainland Asia and the Pacific. This is the first phylogenetic study to extensively sample the Acianthinae outside of Australia, New Zealand, and New Caledonia. By using multiple genes, we achieve good resolution and support, allowing us to propose a revised generic classification system than would both minimize taxonomic changes yet incorporate our new understanding of evolutionary relationships in the group. The phylogeny also reveals that some morphological traits that have been used to define taxonomic groups in the past are quite labile, and indicates a remarkable case of floral convergence. Biogeographical studies indicate a mid-Oligocene origin in Australia with extensive dispersal via West Wind Drift in the southern parts of its range. In the tropical parts of its range, dispersal appears more limited, mostly occurring on a smaller scale---with some dramatic exceptions. Much diversification appears to occur locally, especially within the rapidly uplifting New Guinea. We also employ Next Generation Sequencing genotyping techniques to address relationships within one very recently evolved clade endemic to Australia, the genus Corysanthes Jones et al. This results in unprecedented resolution within and among species, allowing us to evaluate phylogeographic structure and make recommendations on species delimitation. In addition, we present results of an extensive study of the mycorrhizal associations in the Corysanthes clade. All species appear to be strongly associated with one to several undescribed Tulasnella fungi, most of which have not been previously detected in other orchids. Species within the clade clearly differ in regards to their mycorrhizal preferences, though there is a strong environmental signal in their patterns of association.