Morphology and wall ultrastructure of the megaspore Lagenicula (Triletes) variabilis (Winslow, 1962) Arioli et al. (2004) from the Lower Carboniferous of Ohio, USA

Megaspores assigned to Lagenicula (Triletes) variabilis (Winslow, M., 1962. Plant spores and other microfossils from Upper Devonian and Lower Mississippian Rocks of Ohio. Geol. Surv. Prof. Pap. 364, 1–93) Arioli et al., 2004, from the Lower Carboniferous (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. Previous reports of in situ megaspores indicate that Upper Carboniferous Lagenicula (and related forms) derive from the Lepidocarpaceae, that include many of the large arborescent lycopsids that dominated the Euramerican Coal Measure forests. Based on morphological and, to a lesser extent, ultrastructural similarities with Upper Carboniferous forms, it seems likely that Lower Carboniferous Lagenicula also derive from similar plants. This suggests that large arborescent lycopsids typical of the Upper Carboniferous (or at least their precursors) were already present in the Lower Carboniferous, possibly forming forests in similar environments. These may be underrepresented in the fossil record because of the paucity of deposits of this age representing such environments.