This thesis is a study of progymnosperms, an extinct group of mostly Devonian age plants believed to be inherently related to, and most likely the direct ancestors of, seed plants. Progymnosperms are characterised by a unique combination of characters found in `ferns' (free sporing reproduction) and seed plants (wood consisting of secondaryx ylem produced by a bifacial vascular cambium) and therefore play a crucial role in recording the transition between these two plant groups. The focus of this investigation has been to re-analyse progymnosperms, both as individual taxa and also as a distinct biological group, in order to understand better their role in the origin and evolution of seed plants, the dominant element of land vegetation today. Morphological investigations of several progymnosperms and a potential early seed plant form an essential foundation to the conceptual aspects of this work -a palaeophytogeographical study of progymnosperms and early seed plants, and a phylogenetic (cladistic) analysis of plants from the progymnosperm/seed plant transition. Phylogenetic analysis indicates that seed plants are monophyletic, but whether they evolved from within the aneurophytalean grade or the Archaeopteridales Glade could not be determined from the results presented in this thesis. Both the morphological investigation of Telangiopsis roskiliensis and phytogeographical analysis support the Rothwell hypothesis of seed plant evolution (aneurophytalean origin), while the phylogenetic analysis indicates
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:492211 |
| Date | January 2004 |
| Creators | Hammond, Susan Emily |
| Publisher | Cardiff University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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