Permineralized pleuromeid lycopsid remains from the Early Triassic Arcadia Formation, Queensland, Australia

Abstract

Dispersed permineralized cones, stems, rhizomorphs and roots attest to a diversity of pleuromeids in the Early Triassic Bowen Basin of eastern Australia. The lack of organic connection precludes whole plant identification and the material is assigned to form-taxa. Cones are referred to Cylostrobus clavatus Cantrill et Webb, sp. nov., a bisporangiate cone, and Pleuromeia reniformis Cantrill et Webb, sp. nov., a monosporangiate cone. The stem Pleurocaulis rewanense Cantrill et Webb, gen. et sp. nov. has a central exarch protostele surrounded by an aerenchymous inner cortex. Two unlobed rhizomorphs with internal anatomy are recognized, Helicorhiza duckworthensis Cantrill et Webb, gen. et sp. nov. and Cidarophyton rewanense. Duckworthia isoeteformis Cantrill et Webb, gen. et sp. nov. is a form taxon for roots that are monarch with an eccentric vascular bundle and were presumably borne by the rhizomorphs. The anatomy of the plants in conjunction with the sedimentary setting and high palaeolatitudes suggests that the Bowen Basin lycopsids were small ephemeral plants that exploited seasonally wet conditions.