Lycaugea edieae gen. et sp. nov., a Late Devonian Lycopsid from New South Wales, Australia

Abstract

Premise of research. Resolving the time and patterns of origination of the Isoetales that thrived in the wet habitats of the late Paleozoic and have extant representatives in the genus Isoetes requires a better understanding of their early members and precursors. Recent studies conducted for a large part in South China acknowledged the diversification of Middle to Late Devonian taxa that possessed isoetalean traits and either were closely related to the Isoetales or occupied a basal position within this plant order. Recent investigations of Late Devonian floras from Australia show that this area, on the northeastern edge of Gondwana, also yields taxa with combinations of characters unknown elsewhere. Methodology. The anatomy and external morphology of an anatomically preserved fragment of a lycopsid axis from the Famennian locality of Barraba, in New South Wales, are described. The new specimen is compared to lycopsid taxa on the basis of anatomically preserved specimens ranging from the Middle Devonian to the Late Carboniferous. Pivotal results. The Barraba specimen shows a new combination of characters consisting of a medullated protostele, three-zoned cortex with a wide middle cortex, homogeneous primary outer cortex, presumably deciduous leaves, and slightly protuberant widely spaced leaf bases. Leaf bases show a single large parichnos and are covered adaxially by a thick translucent layer. The specimen is interpreted as the distal branch of a new arborescent taxon, Lycaugea edieae. Taxa with the closest morphoanatomical characters, such as Wexfordia hookense, belong to the Isoetales and are found in deposits of Europe and the eastern United States. Conclusions. Lycaugea edieae is the third lycopsid taxon described from Barraba, which, to date, has yielded a majority of spore-producing plants. It increases the diversity of the early Isoetales around the Devonian-Carboniferous boundary. The Barraba flora is more similar to the contemporaneous flora in southern Laurussia than to that in China.