Cycadales of the English Wealden

• Main Author: Cusack-Drury, Helen Alexandra
• Published: University of Manchester 2001
• Subjects: 561
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.496648

A taxonomic revision of the Cycadales in the English Wealden fossil flora constitutes the major part of this thesis. It is prefaced by short reviews of the geological setting and the previous work on the fossil flora. The nature of extant members of the Cycadales and their geological and evolutionary history are reviewed. Morphological studies together with light and scanning electron microscopy of epidermal features have allowed diagnosis and/or description of. sixteen leaf species, seven of them new, assigned to the form-genera Becklesia Seward, Ctenis Lindley & Hutton, Doratophyllum Harris, Nilssonia Brongniart, Paracycas Harris, Pseudoctenis Seward and one new genus is erected. Nilssonia schaumburgensis (Dunker) is reconstructed here as a liana-type woody climber. Four new species of scale leaves are put into the genus Deltolepis Harris which is new to the English Wealden. New evidence has revealed all known types of cycad cones with both lineages of cycad female cones represented by one species of Crossozamia Pomel (a megasporophyll of the Cycas-type) and one species of Zamiostrobus Endlicher (a female cone of the Zamia-type) with aborted ovules present. Male cones are represented by one species of Androstobus Schimper containing pollen. The Zamiostrobus and Androstobus species, for which 3D reconstructions are presented, now represent the best known cycad cones in any Mesozoic flora. Ten different types of isolated seeds are included in the genus Carpolithus Linnaeus. One trunk species is assigned to the genus Bucklandia Presl. Several species of extant cycads have been studied in microscopic detail for comparative purposes. Parallels are drawn between Mesozoic and extant genera and species, confirming the `Living Fossil' status long assigned to extant cycads. Laboratory methods employed and details of all fossil specimens studied are appended.