A Molecular Systematic Study of the Xylariales (Ascomycota)

This dissertation, "A Molecular Systematic Study of the Xylariales (ascomycota)" by Gavin James, Smith, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Abstract of thesis entitled A MOLECULAR SYSTEMATIC STUDY OF THE XYLARIALES (ASCOMYCOTA) Submitted by Gavin J.D. Smith for the degree of Doctor of Philosophy at The University of Hong Kong in April 2003 A number of often conflicting, morphology-based classifications have been suggested for the Xylariales. No attempt has previously been undertaken to test these classifications using molecular data. Phylogenetic relationships of six accepted families of the Xylariales (Amphisphaeriaceae, Clypeosphaeriaceae, Diatrypaceae, Graphostromataceae, Hyponectriaceae and Xylariaceae) and several members of the Apiosporaceae were investigated using separate and combined analyses of 28S and 18S rDNA gene fragments. Phylogenetic analyses were conducted using maximum and weighted parsimony, and maximum likelihood criteria. The Xylariales sensu Eriksson et al. (2003) was found to be paraphyletic due to the inclusion of the Apiosporaceae within the order. The Xylariales is redefined as a monophyletic order containing seven families - Amphisphaeriaceae, Apiosporaceae, Clypeosphaeriaceae, Diatrypaceae, Graphostromataceae, Hyponectriaceae and Xylariaceae. Levels of phylogenetic signal and support for relationships within the Xylariales were low and the 28S and 18S rDNA data proved inadequate to fully resolve familial relationships within the order. The phylogenetic relationships of genera in the Xylariaceae were investigated using ITS sequence data. Different alignments of subsets of the ITS sequences were conducted to assess the suitability of the fragment in studying the Xylariaceae. Relationships had high bootstrap support and so the ITS region was deemed to be suitable for phylogenetic studies of the Xylariaceae. The ITS analysis shows the Xylariaceae is not monophyletic and contains morphologically distinct Hypoxyloid and Xylarioid groups. The Hypoxyloid group is related to other families of the Xylariales, and the Xylarioid group appears phylogenetically isolated. The separation of the Xylariaceae had very high bootstrap support in all molecular analyses. Hypoxyloid taxa include species of Biscogniauxia, Camillea, Daldinia, Graphostroma and Hypoxylon, and Xylarioid taxa include Astrocystis, Entoleuca, Nemania, Rosellinia and Xylaria. The Hypoxyloid and Xylarioid groups were found to differ in anamorph form, and in ascus and spore characteristics. Both the Hypoxyloid and Xylarioid taxa were further divided into morphologically distinct subgroups. Hypoxyloid taxa were separated based on absence or presence of bipartite stromata and KOH-extractable pigments, and Xylarioid taxa were separated according to developmental relationships between the anamorph and teleomorph. A number of taxonomic revisions based on morphological data were also suggested. The Graphostromataceae was found to be an invalid family as Graphostroma was found to be closely related to Biscogniauxia. Graphostroma should therefore be transferred to the Xylariaceae. Astrocystis is a distinct and monophyletic genus; while species of Nemania, except N. bipapillata, formed a well supported clade. Xylaria is paraphyletic due to the inclusion of Kretzschmaria species in the clade. It was suggested that Kretzschmaria be synonymised with Xylaria, as they differ primarily on stromatal characters, and are microscopically indistinguishable. Rosellinia necatrix was found to be synonymous with R. bo