A new late devonian isoetalean lycopsid from new South Wales, Australia: Cymastrobus irvingii gen. et sp. nov

Abstract

In Australia, lycopsids are abundant in early land plant assemblages, leading to the concepts of a “Baragwanathia flora” extending from the late Silurian to the Early Devonian, and a “Leptophloeum flora” characterizing the Late Devonian. Yet, the taxonomic status and systematic affinities of a large number of lycopsid remains from the Devonian of Australia are poorly resolved. The contribution of such lycopsids to the diversification of the group and the evolution of the rhizomorphic lycopsids is unknown. In this paper we investigate the three-dimensional organization of a new structurally preserved cone using X-ray synchrotron microtomography. This large and compact bisporangiate cone, which was collected at Barraba, a Famennian locality in northern New South Wales, represents a new genus, Cymastrobus. Its sporophylls are comprised of a poorly preserved lamina and a long narrow pedicel enlarging distally and possessing an abaxial keel and a heel. Megasporangia contain a large number of megaspores. Their central body shows several rows of small circular structures surrounding the trilete mark. Microspore remains are of the Endosporites-type. Cymastrobus is close to the contemporaneous genus Bisporangiostrobus and to the Carboniferous taxon Flemingites. It may have occupied a basal position in the phylogeny of the rhizomorphic lycopsids.