Morphology and wall ultrastructure of the megaspore Lagenicula (Triletes) mixta (Winslow 1962) comb. nov. from the Carboniferous (Early Mississippian: mid Tournaisian) of Ohio, USA

Megaspores assigned to Lagenicula (Triletes) mixta (Winslow, M., 1962. Plant Spores and Other Microfossils from Upper Devonian and Lower Mississippian Rocks of Ohio. Geol. Surv., Prof. Paper 364, 1-93.) comb. nov., from the Carboniferous (Early Mississippian: mid Tournaisian) of northeastern Ohio, USA, have been analysed using light microscopy (LM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). These studies provide new information on morphology, gross structure and wall ultrastructure. This taxon has a confused taxonomic history, and the new morphological information allows recognition as a distinct species that can be placed with the genus Lagenicula as a new combination. Morphological/ultrastructural studies confirm the lycopsid affinities of this megaspore and it is suggested that it probably derived from an arborescent lycopsid that belonged with the Lepidocarpaceae. Thus it is an early example of a megaspore derived from an arborescent lycopsid of the type that went on to dominate the Euramerican Coal Measure forests. The Ohio Tournaisian megaspore assemblage is surprisingly diverse revealing an interesting insight into vegetation ecology at this poorly understood time in plant history.