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A valuable contribution to the on-going discussions on evolution within the Orchid family. Dressler's work delimits several major natural groups and emphasises areas needing further study.
Orchidaceae - Phylogeny.
Considering the significance of the basal Epidendroideae in understanding patterns of morphological evolution within the subfamily, it is surprising that a robust hypothesis of historical relationships has not been presented for these orchids. This is the first study to improve both taxon and character sampling. The phylogenetic study of the basal Epidendroideae consisted of two components. A molecular phylogeny using three loci representing each of the plant genomes including gap characters is presented for the basal Epidendroideae. The results of the morphological analysis results support many of the traditional views of tribal composition, but do not fully resolve relationships among many of the tribes. A robust hypothesis is presented based on the results of a total evidence analysis (TEA) using three molecular loci, gap characters and morphology. Palmorchis is sister to Neottieae, followed successively by Triphoreae sister to Epipogium, then Sobralieae. Tropidieae is sister to the advanced Epidendroideae, and this sister to Nervilieae and Gastrodieae. Diceratostele gabonensis groups within this clade. Morphology is studied mapped onto the TEA and discussed. As part of the study of the basal Epidendroideae, a monograph of the orchid genus Psilochilus(Triphoreae) was prepared in order to better understand the natural variation within the genus. Based on this work, there are seven species recognized, of which one is a newly described species, Psilochilus ecuadoriensis, from lowlands of western Ecuador. A molecular phylogenetic study of the genus, representing five of the seven species, was performed using the plastid trn L-F intergenic spacer. Psilochilus physurifolius is at the base of the genus. Psilochilus modestus and P. macrophyllus form a clade and this sister to P. mollis and P. ecuadoriensis. Morphological characters that were useful for species delimitations were mapped onto this tree. Psilochilus is monophyletic based on sequence data, and is supported by the presence of two calli on the labellum and petiolate leaves.
Remarkably, subtribe Pleurothallidinae (Orchidaceae) accounts for 15-20% of total orchid diversity with>4,000 species in 29 genera. One of the most extraordinary genera of 'pleurothallids' is Porroglossum, which accounts for 54 described species that are distributed throughout Andean cloud forests in South America. In actuality, the flowers of Porroglossum set it apart from nearly all other 'pleurothallids' because the labellum, when physically stimulated, actively snaps inward thrusting pollinators against the column to ensure pollination. Porroglossum is also an exceedingly young plant lineage that arose between approximately 3 and 4 million years ago. Despite the evolution of an elaborate pollination trap, little is known about the biology of Porroglossum, which presents unique opportunities for evolutionary studies. As a result, we present the first phylogenetic study of the genus Porroglossum. By sequencing multiple genetic markers, we achieve good resolution and support, which allows us to propose a revised subgeneric classification system incertae sedis. Additionally, we found that individual gene trees vary in terms of resolution and statistical support. In particular, we note that species P. sergioi and P. teaguei switch clades when comparing the plastid and nuclear datasets, which suggests potential hybridization when coupled with geographic data that indicates sympatry among their proposed parents. Moreover, we employ Next-Generation Sequencing, in the form of genotyping-by-sequencing, to address phylogenetic uncertainty that stems from the Sanger sequencing study. The GBS study illustrates the importance of extensive parameter testing when reconstructing the evolutionary history of non-model organisms with de novo assembled loci. Specifically, parameter testing helps maximize the recovery of phylogenetically informative characters while reducing the amount of sequencing errors and paralogs in the final dataset. This results in unprecedented resolution thereby resolving deep internal nodes as well as interspecific relationships within Porroglossum. Furthermore, we present the first kinematics study in a phylogenetic context that addresses the active floral snap-trap. Continuous traits appear to be strongly correlated with the evolutionary history of Porroglossum. Within the genus, we note clades with delayed and undelayed snap-traps that take multiple minutes or only a few seconds to close respectively. Lastly, snap-trap traits appear to be correlated with elevation.
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.
Plastid Genome Evolution, Volume 85 provides a summary of recent research on plastid genome variation and evolution across photosynthetic organisms. It covers topics ranging from the causes and consequences of genomic changes, to the phylogenetic utility of plastomes for resolving relationships across the photosynthetic tree of life. This newly released volume presents thorough, up-to-date information on coevolution between the plastid and nuclear genomes, with chapters on plastid autonomy vs. nuclear control over plastid function, establishment and genetic integration of plastids, plastid genomes in alveolate protists, plastid genomes of glaucophytes, the evolution of the plastid genome in chlorophyte and streptophyte green algae, and more. Provides comprehensive coverage of plastid genome variation by leading researchers in the field Presents a broad range of taxonomic groups, ranging from single and multicellular algae, to the major clades of land plants Includes thorough, up-to-date information on coevolution between the plastid and nuclear genomes